99388113

Campbell SP

Williams DA

Frueh BR

Lynch GS

Contractile activation characteristics of single permeabilized fibres from levator palpebrae superioris, orbicularis oculi and vastus lateralis muscles from humans [In Process Citation]

Eng

19990925

1999 Sep 1

0022-3751

J Physiol (Lond)

615-22

M

ENGLAND

519 Pt 2

JQV

AUTHOR

1. We investigated the contractile activation characteristics of single membrane-permeabilized fibres from the following muscles from humans: the levator palpebrae superioris (LPS), an extraocular muscle; the orbicularis oculi (OO), a facial muscle; and the vastus lateralis (VL), a major muscle of the thigh. 2. Single permeabilized muscle fibres were isolated from each of the different muscles, attached to a sensitive force transducer and activated by rapid immersion in buffered solutions of varying [Ca2+] and [Sr2+]. Fibres were allocated into discrete populations based on their contractile characteristics, including their differential force responses during Ca2+ and Sr2+ activation. 3. With the exception of one fibre from the LPS, all 152 fibres sampled from the three different human muscles could be classified into either population I (slow, type I) or population II (fast, type II) based on their force-pCa(pSr) relations. The LPS muscle fibre which was unable to be classified into the two major fibre populations displayed a combination of the typical force-pCa(pSr) relations for mammalian fast and slow muscle fibres. 4. Although fibres from the LPS, OO and VL muscles had similar differential sensitivities to Ca2+and Sr2+, the steepness of the force-pCa(pSr) curves for fibres from the LPS and OO muscles were highly variable compared with those for fibres from the VL muscle. Specific forces (N cm-2) of the smaller diameter fibres from the LPS and OO muscles were significantly lower than those of fibres from the VL muscle. 5. The differences in the contractile activation characteristics between fibres from the VL muscle and those of fibres from facial (OO) muscles and extraocular (LPS) muscles, reflect the differences in their fibre composition that are responsible for their functional specificity.

Muscle and Cell Physiology Laboratory, Department of Physiology, The University of Melbourne, Parkville, Victoria 3052, Australia.

O:099

0010457076

PHY_9327

http://www.journals.cup.org/owa_dba/owa/approval?sjid=PHY&said=9327&spii =S0022375199093278

J Physiol (Lond) 1999 Sep 1;519 Pt 2:615-22

99388104

Edman KA

The force bearing capacity of frog muscle fibres during stretch: its relation to sarcomere length and fibre width [In Process Citation]

Eng

19990925

1999 Sep 1

0022-3751

J Physiol (Lond)

515-26

M

ENGLAND

519 Pt 2

JQV

AUTHOR

1. Single fibres isolated from the anterior tibialis muscle of Rana temporaria were tetanized (0.9-1.8 C) while a marked ( approximately 1 mm) segment was held at constant length by feedback control. Force enhancement was produced by applying a controlled stretch ramp to the fibre segment during the tetanus plateau, the steady force reached during stretch being used as a measure of the maximum force that the myosin cross-bridges can hold before they detach. 2. The amplitude of force enhancement during stretch did not vary in proportion to the isometric force as the sarcomere length was changed, maximum force enhancement being attained near 2.4 &mgr;m sarcomere length compared with 2.0 &mgr;m for the isometric force. 3. The influence of fibre width on the force enhancement-sarcomere length relationship was evaluated by normalizing force enhancement to the tetanic (pre-stretch) force in this way allowing for the differences in myofilament overlap at the various lengths. The amplitude of force enhancement (normalized to the tetanic force) increased by approximately 70 % as the relative width of the myofilament lattice was reduced from a nominal value of 1.05 at a sarcomere length of 1.8 &mgr;m to 0.85 at a sarcomere length of 2.8 &mgr;m. 4. Changes in fibre width equivalent to those produced by altering the sarcomere length were produced by varying the tonicity of the extracellular medium. Force enhancement, normalized to the control isometric force at each tonicity, exhibited a width dependence that agreed well with that described in the previous point. Stretch ramps applied to frog skinned muscle fibres during calcium-induced contracture likewise resulted in a greater force enhancement during stretch after reducing the fibre width by osmotic compression. 5. The results suggest that the strength of binding of the myosin cross- bridges, unlike the isometric force, varies with the lateral distance between the myofilaments.

Department of Pharmacology, University of Lund, Solvegatan 10, S-223 62 Lund, Sweden.

O:099

0010457067

PHY_8921

http://www.journals.cup.org/owa_dba/owa/approval?sjid=PHY&said=8921&spii =S0022375199089218

J Physiol (Lond) 1999 Sep 1;519 Pt 2:515-26

99310898

Parris JR

Cobban HJ

Littlejohn AF

MacEwan DJ

Nixon GF

Tumour necrosis factor-alpha activates a calcium sensitization pathway in guinea-pig bronchial smooth muscle.

Eng

p42(Mapk) Kinase/metabolism

Animal

Bronchi/*drug effects

Calcium/metabolism/physiology

Calcium Signaling/*drug effects

Guinea Pigs

In Vitro

Male

Muscle Contraction/drug effects

Muscle, Smooth/*drug effects

Myosin Light Chains/metabolism

Recombinant Proteins/pharmacology

Sphingomyelin Phosphodiesterase/metabolism

Support, Non-U.S. Gov't

Tumor Necrosis Factor/*pharmacology

EC 2.7.10.- (p42(Mapk) Kinase)

EC 3.1.4.12 (Sphingomyelin Phosphodiesterase)

0 (Myosin Light Chains)

0 (Recombinant Proteins)

0 (Tumor Necrosis Factor)

7440-70-2 (Calcium)

JOURNAL ARTICLE

19991020

1999 Jul 15

0022-3751

J Physiol (Lond)

561-9

M

ENGLAND

518 ( Pt 2)

JQV

Author

199912

1. The effects of tumour necrosis factor-alpha (TNF) on guinea-pig bronchial smooth muscle contractility were investigated. 2. The Ca2+- activated contractile response of permeabilized bronchial smooth muscle strips was significantly increased after incubation with 1 microgram ml- 1 TNF for 45 min. This TNF-induced effect was not due to a further increase in intracellular Ca2+. 3. The TNF-induced Ca2+ sensitization was, at least partly, the result of an increase in myosin light chain20 phosphorylation. 4. The intracellular signalling pathway involved in this effect of TNF was further investigated. Sphingomyelinase, a potential mediator of TNF, had no effect on Ca2+ sensitivity of permeabilized bronchial smooth muscle. Also, p42/p44 mitogen-activated protein kinase (p42/p44mapk), activated by TNF in some cell types, did not show an increased activation in bronchial smooth muscle after TNF treatment. 5. In conclusion, TNF may activate a novel signalling pathway in guinea-pig bronchial smooth muscle leading to an increase in myosin light chain20 phosphorylation and a subsequent increase in Ca2+ sensitivity of the myofilaments. This pathway does not appear to involve sphingomyelinase-liberated ceramides or activation of p42/p44mapk. Given the importance of TNF in asthma, this TNF-induced Ca2+ sensitization of the myofilaments may represent a mechanism responsible for airway hyper-responsiveness.

Department of Biomedical Sciences, Institute of Medical Sciences, University of Aberdeen, Aberdeen, UK.

0010381600

PHY_8883

http://www.journals.cup.org/owa_dba/owa/approval?sjid=PHY&said=8883&spii =S0022375199088833

J Physiol (Lond) 1999 Jul 15;518 ( Pt 2):561-9

99288149

He ZH

Chillingworth RK

Brune M

Corrie JE

Webb MR

Ferenczi MA

The efficiency of contraction in rabbit skeletal muscle fibres, determined from the rate of release of inorganic phosphate.

Eng

Adenosine Triphosphate/analogs & derivatives/metabolism

Adenosinetriphosphatase/*metabolism

Animal

In Vitro

Kinetics

Muscle Contraction/*physiology

Muscle Fibers/*physiology

Muscle, Skeletal/*physiology

Phosphates/*metabolism

Photolysis

Rabbits

Sarcomeres/*physiology

Temperature

EC 3.6.1.3 (Adenosinetriphosphatase)

0 (Phosphates)

56-65-5 (Adenosine Triphosphate)

67030-27-7 (P(3)-1-(2-nitro)phenylethyladenosine 5'-triphosphate)

JOURNAL ARTICLE

19990802

1999 Jun 15

0022-3751

J Physiol (Lond)

839-54

M

ENGLAND

517 ( Pt 3)

JQV

Author

199910

1. The relationship between mechanical power output and the rate of ATP hydrolysis was investigated in segments of permeabilized fibres isolated from rabbit psoas muscle. 2. Contractions were elicited at 12 degrees C by photolytic release of ATP from the P3 -1-(2-nitrophenyl) ester of ATP (NPE-caged ATP). Inorganic phosphate (Pi) release was measured by a fluorescence method using a coumarin-labelled phosphate binding protein. Force and sarcomere length were also monitored. 3. ATPase activity was determined from the rate of appearance of Pi during each phase of contraction. The ATPase rate was 10.3 s-1 immediately following release of ATP and 5. 1 s-1 during the isometric phase prior to the applied shortening. It rose hyperbolically with shortening velocity, reaching 18.5 s-1 at a maximal shortening velocity > 1 ML s-1 (muscle lengths s-1). 4. Sarcomeres shortened at 0.09 ML s-1 immediately following the photolytic release of ATP and at 0.04 ML s-1 prior to the period of applied shortening. The high initial ATPase rate may be largely attributed to initial sarcomere shortening. 5. During shortening, maximal power output was 28 W l-1. Assuming the free energy of hydrolysis is 50 kJ mol-1, the efficiency of contraction was calculated from the power output at each shortening velocity. The maximum efficiency was 0.36 at a shortening velocity of 0.27 ML s-1, corresponding to a force level 51 % of that in the isometric state. 6. At the maximal shortening velocity, only 10 % of the myosin heads are attached to the thin filaments at any one time.

National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK.

0010358123

PHY_8978

http://www.journals.cup.org/owa_dba/owa/approval?sjid=PHY&said=8978&spii =S0022375199089784

J Physiol (Lond) 1999 Jun 15;517 ( Pt 3):839-54

99288148

Hanley PJ

Young AA

LeGrice IJ

Edgar SG

Loiselle DS

3-Dimensional configuration of perimysial collagen fibres in rat cardiac muscle at resting and extended sarcomere lengths.

Eng

Muscle Fibers/*physiology

Analysis of Variance

Animal

Collagen/*ultrastructure

Heart/physiology

Heart Ventricle

Image Processing, Computer-Assisted

Microscopy, Confocal

Microscopy, Electron

Models, Structural

Myocardium/cytology/*ultrastructure

Rats

Rats, Wistar

Sarcomeres/*physiology/*ultrastructure

Support, Non-U.S. Gov't

9007-34-5 (Collagen)

JOURNAL ARTICLE

19990802

1999 Jun 15

0022-3751

J Physiol (Lond)

831-7

M

ENGLAND

517 ( Pt 3)

JQV

Author

199910

1. We have used fluorescence confocal laser scanning microscopy to attain the three-dimensional (3-D) microstructure of perimysial collagen fibres over the range of sarcomere lengths (1.9-2.3 micrometers) in which passive force of cardiac muscle increases steeply. 2. A uniaxial muscle preparation (right ventricular trabecula of rat) was used so that the 3-D collagen configuration could be readily related to sarcomere length. Transmission electron microscopy showed that these preparations were structurally homologous to ventricular wall muscle. 3. Trabeculae were mounted on the stage of an inverted microscope and fixed at various sarcomere lengths. After a trabecula was stained with the fluorophore Sirius Red F3BA and embedded in resin, sequential optical sectioning enabled 3-D reconstruction of its perimysial collagen fibres. The area fraction of these fibres, determined from the cross-sections of seven trabeculae, was 10.5 +/- 3.9 % (means +/- s.d.). 4. The reconstructed 3-D images show that perimysial collagen fibres are wavy (as distinct from coiled) cords which straighten considerably as the sarcomere length is increased from 1.85 +/- 0.06 micrometer (near-resting length) to 2.3 +/- 0.04 micrometer (means +/- s.d., n = 4). These observations are consistent with the notion that the straightening of these fibres is responsible for limiting extension of the cardiac sarcomere to a length of approximately 2.3 micrometers.

Department of Physiology, School of Medicine and Health Science, University of Auckland, Auckland, New Zealand. p_hanley98@hotmail.com

0010358122

PHY_9009

http://www.journals.cup.org/owa_dba/owa/approval?sjid=PHY&said=9009&spii=S0022375199090092

J Physiol (Lond) 1999 Jun 15;517 ( Pt 3):831-7

99272460

Yoshii A

Iizuka K

Dobashi K

Horie T

Harada T

Nakazawa T

Mori M

Relaxation of contracted rabbit tracheal and human bronchial smooth muscle by Y-27632 through inhibition of Ca2+ sensitization.

Eng

Amides/*pharmacology

Animal

Bronchi/*metabolism

Calcium/*antagonists & inhibitors

Carbachol/pharmacology

Cholinergic Agents/pharmacology

Detergents/pharmacology

Dose-Response Relationship, Drug

Endothelin-1/pharmacology

G-Proteins/metabolism

Guanosine 5'-O-(3-Thiotriphosphate)/pharmacology

Human

Muscle Contraction

Muscle, Smooth/*metabolism

Myosin-Light-Chain Kinase/metabolism

Octoxynol/pharmacology

Oxazoles/pharmacology

Phosphodiesterase Inhibitors/pharmacology

Phospholipase C/pharmacology

Protein-Serine-Threonine Kinases/metabolism

Pyridines/*pharmacology

Rabbits

Signal Transduction

Support, Non-U.S. Gov't

Trachea/*metabolism

1-Methyl-3-isobutylxanthine/pharmacology

EC 2.7.1.117 (Myosin-Light-Chain Kinase)

EC 2.7.10 (Protein-Serine-Threonine Kinases)

EC 2.7.10.- (Rho-associated kinase)

EC 3.1.4.3 (Phospholipase C)

0 (Amides)

0 (Cholinergic Agents)

0 (Detergents)

0 (Endothelin-1)

0 (G-Proteins)

0 (Oxazoles)

0 (Phosphodiesterase Inhibitors)

0 (Pyridines)

101932-71-2 (calyculin A)

138381-45-0 (Y 27632)

28822-58-4 (1-Methyl-3-isobutylxanthine)

37589-80-3 (Guanosine 5'-O-(3-Thiotriphosphate))

51-83-2 (Carbachol)

7440-70-2 (Calcium)

9002-93-1 (Octoxynol)

JOURNAL ARTICLE

19990707

1999 Jun

1044-1549

Am J Respir Cell Mol Biol

1190-200

M

UNITED STATES

6

20

AOB

Author

199909

The mechanism of Ca2+ sensitization of contraction has not been elucidated in airway smooth muscle (SM). To determine the role of a small G protein, rhoA p21, and its target protein, rho-associated coiled coil-forming protein kinase (ROCK), in receptor-coupled Ca2+ sensitization of airway SM, we studied the effect of (+)-(R)-trans-4-(1- aminoethyl)-N-(4-pyridyl)cyclohexane carboxamide dihydrochloride, monohydrate (Y-27632), a ROCK inhibitor, on isometric contractions in rabbit tracheal and human bronchial SM. Y-27632 completely reversed 1 microM carbachol (CCh)-induced contraction of intact trachea with a concentration producing half-maximum inhibition of effect (IC50) of 1.29 +/- 0.2 microM (n = 5). Although 4beta-phorbol 12,13-dibutyrate (1 microM)-induced Ca2+ sensitization was relatively resistant to Y-27632 in alpha-toxin-permeabilized trachea, CCh (100 microM) plus guanosine triphosphate (GTP) (3 microM)- and guanosine 5'-O-(3'-thiotriphosphate) (10 microM)-induced contractions were relaxed completely by Y-27632 with IC50 of 1.44 +/- 0.3 (n = 6) and 1.15 +/- 0.3 microM (n = 6). Endothelin-1 (1 microM) plus GTP (3 microM)- developed force was also reversed by Y-27632 with IC50 of 4. 10 +/- 1.1 microM (n = 6) in the alpha-toxin-permeabilized bronchus. Both the rabbit and human SM expressed rhoA p21, ROCK I, and its isoform ROCK II. Collectively, rho/ROCK-mediated Ca2+ sensitization plays a central role in the sustained phase of airway SM contraction, and selective inhibition of this pathway may become a new strategy to resolve airflow limitation in asthma.

First Department of Internal Medicine, Faculty of Medicine, School of Medicine, Gunma University, Maebashi, Gunma, Japan.

0010340938

Am J Respir Cell Mol Biol 1999 Jun;20(6):1190-200

99045480

He ZH

Ferenczi MA

Brune M

Trentham DR

Webb MR

Somlyo AP

Somlyo AV

Time-resolved measurements of phosphate release by cycling cross- bridges in portal vein smooth muscle.

Eng

Adenosine Triphosphate/analogs & derivatives/metabolism

Adenosinetriphosphatase/metabolism

Animal

Biophysics

In Vitro

Kinetics

Muscle Contraction/physiology

Muscle, Smooth, Vascular/*metabolism/physiology

Myosin/metabolism

Permeability

Phosphates/*metabolism

Phosphorylation

Photolysis

Portal Vein/metabolism/physiology

Rabbits

Support, Non-U.S. Gov't

Support, U.S. Gov't, P.H.S.

EC 3.6.1.3 (Adenosinetriphosphatase)

0 (Myosin)

0 (Phosphates)

56-65-5 (Adenosine Triphosphate)

67030-27-7 (P(3)-1-(2-nitro)phenylethyladenosine 5'-triphosphate)

JOURNAL ARTICLE

HL19242/HL/NHLBI

19990125

1998 Dec

0006-3495

Biophys J

3031-40

M

UNITED STATES

6

75

A5S

Author

199903

The rate of release of inorganic phosphate (Pi) from cycling cross- bridges in rabbit portal-anterior mesenteric vein smooth muscle was determined by following the fluorescence of the Pi-reporter, MDCC-PBP (Brune, M., J. L. Hunter, S. A. Howell, S. R. Martin, T. L. Hazlett, J. E. T. Corrie, and M. R. Webb. 1998. Biochemistry. 37:10370-10380). Cross-bridge cycling was initiated by photolytic release of ATP from caged-ATP in Triton-permeabilized smooth muscles in rigor. When the regulatory myosin light chains (MLC20) had been thiophosphorylated, the rate of Pi release was biphasic with an initial rate of 80 microM s-1 and amplitude 108 microM, decreasing to 13.7 microM s-1. These rates correspond to fast and slow turnovers of 1.8 s-1 and 0.3 s-1, assuming 84% thiophosphorylation of 52 microM myosin heads. Activation by Ca2+- dependent phosphorylation subsequent to ATP release resulted in slower Pi release, paralleling the rate of contraction that was also slower than after thiophosphorylation, and was also biphasic: 51 microM s-1 and 13.2 microM s-1. These rates suggest that the activity of myosin light chain kinase and phosphatase ("pseudo-ATPase") contributes <20% of the ATP usage during cross-bridge cycling. The extracellular "ecto- nucleotidase" activity was reduced eightfold by permeabilization, conditions in which the ecto-ADPase was 17% of the ecto-ATPase. Nevertheless, the remaining ecto-ATPase activity reduced the precision of the estimate of cross-bridge ATPase. We conclude that the transition from fast to slow ATPase rates reflects the properties and forces directly acting on cross-bridges, rather than the result of a time- dependent decrease in activation (MLC20 phosphorylation) occurring in intact smooth muscle. The mechanisms of slowing may include the effect of positive strain on cross-bridges, inhibition of the cycling rate by high affinity Mg-ADP binding, and associated state hydrolysis.

National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom.

0009826623

Biophys J 1998 Dec;75(6):3031-40

99007358

He Z

Stienen GJ

Barends JP

Ferenczi MA

Rate of phosphate release after photoliberation of adenosine 5'- triphosphate in slow and fast skeletal muscle fibers.

Eng

Adenosine Diphosphate/pharmacology

Adenosine Triphosphate/*analogs & derivatives/metabolism

Animal

Calcium/pharmacology

Carrier Proteins/metabolism

Coumarins/metabolism

Fluorescent Dyes

Kinetics

Muscle Contraction/physiology

Muscle Fibers, Fast-Twitch/*metabolism

Muscle Fibers, Slow-Twitch/*metabolism

Muscle, Skeletal/*physiology

Phosphates/*metabolism

Photolysis

Psoas Muscles/physiology

Rabbits

Sarcomeres/metabolism

Support, Non-U.S. Gov't

0 (phosphate-binding proteins)

0 (Carrier Proteins)

0 (Coumarins)

0 (Fluorescent Dyes)

0 (Phosphates)

156571-46-9 (N-(2-(1-maleimidyl)ethyl)-7-(diethylamino)coumarin-3- carboxamide)

56-65-5 (Adenosine Triphosphate)

58-64-0 (Adenosine Diphosphate)

67030-27-7 (P(3)-1-(2-nitro)phenylethyladenosine 5'-triphosphate)

7440-70-2 (Calcium)

JOURNAL ARTICLE

19981204

1998 Nov

0006-3495

Biophys J

2389-401

M

UNITED STATES

5

75

A5S

Author

199902

Inorganic phosphate (Pi) release was determined by means of a fluorescent Pi-probe in single permeabilized rabbit soleus and psoas muscle fibers. Measurements of Pi release followed photoliberation of approximately 1.5 mM ATP by flash photolysis of NPE-caged ATP in the absence and presence of Ca2+ at 15 degrees C. In the absence of Ca2+, Pi release occurred with a slow rate of 11 +/- 3 microM . s-1 (n = 3) in soleus fibers and 23 +/- 1 microM . s-1 (n = 10) in psoas fibers. At saturating Ca2+ concentrations (pCa 4.5), photoliberation of ATP was followed by rapid force development. The initial rate of Pi release was 0.57 +/- 0.05 mM . s-1 in soleus (n = 13) and 4.7 +/- 0.2 mM . s-1 in psoas (n = 23), corresponding to a rate of Pi release per myosin head of 3.8 s-1 in soleus and 31.5 s-1 in psoas. Pi release declined at a rate of 0.48 s-1 in soleus and of 5.2 s-1 in psoas. Pi release in soleus was slightly faster in the presence of an ATP regenerating system but slower when 0.5 mM ADP was added. The reduction in the rate of Pi release results from an initial redistribution of cross-bridges over different states and a subsequent ADP-sensitive slowing of cross- bridge detachment.

National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom.

0009788934

Biophys J 1998 Nov;75(5):2389-401

98399940

Slawnych MP

Morishita L

Bressler BH

Image-analysis-based assessment of the effects of the "Ca2+-jump" technique on sarcomere uniformity.

Eng

Animal

Calcium/*diagnostic use

Image Processing, Computer-Assisted

In Vitro

Muscle Contraction/physiology

Muscle Fibers/*physiology/*ultrastructure

Muscle Relaxation/physiology

Muscle, Skeletal/*physiology/*ultrastructure

Rabbits

Sarcomeres/*physiology/*ultrastructure

Solutions

Spectroscopy, Fourier Transform Infrared

Support, Non-U.S. Gov't

0 (Solutions)

7440-70-2 (Calcium)

JOURNAL ARTICLE

19981105

1998 Sep

8750-7587

J Appl Physiol

955-61

M

UNITED STATES

3

85

HEG

Author

199901

A new image analysis-based technique was used to quantitatively examine the effects of the "Ca2+-jump" activation protocol on the maintenance of fiber quality in skinned rabbit psoas muscle fiber segments. Specifically, contractions in pCa 4.6 were preceded by short-duration "preactivation" soaks in a solution in which EGTA was replaced with the low-Ca2+ buffering capacity analog hexamethylenediamine-N, N, N', N'- tetraacetate, which facilitated rapid Ca2+ equilibration within the fiber segments. Fiber quality was assessed by examining the Fourier spectra of the muscle fiber images before, during, and after activation. Segment lengths were typically below 500 micrometer, thus allowing the majority of the sarcomeres to be visualized in the field of view (x200 and x400 magnification). The preactivation protocol resulted in less deterioration of fiber quality with repetitive activation. In addition, there was also a significant reduction in the time required to reach the 50% level of maximum tension, with no significant change in the maximum tension level.

Department of Anatomy, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3. slawnych@cortex.biomed.mcgill.ca

0009729569

J Appl Physiol 1998 Sep;85(3):955-61

98365280

Sun Y

Caputo C

Edman KA

Effects of BAPTA on force and Ca2+ transient during isometric contraction of frog muscle fibers.

Eng

Animal

Calcium/*metabolism

Chelating Agents/*pharmacology

Egtazic Acid/*analogs & derivatives/pharmacology

In Vitro

Isometric Contraction/*drug effects

Kinetics

Muscle Fibers/drug effects/*physiology

Muscle, Skeletal/drug effects/*physiology

Rana temporaria

Sarcomeres/drug effects/physiology

Support, Non-U.S. Gov't

Time Factors

0 (Chelating Agents)

67-42-5 (Egtazic Acid)

7440-70-2 (Calcium)

85233-19-8 (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid)

JOURNAL ARTICLE

19980916

1998 Aug

0002-9513

Am J Physiol

C375-81

M

UNITED STATES

2 Pt 1

275

3U8

Author

199811

The effects of 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) on force and intracellular Ca2+ transient were studied during isometric twitches and tetanuses in single frog muscle fibers. BAPTA was added to the bathing solution in its permeant AM form (50 and 100 microM). There was no clear correlation between the changes in force and the changes in Ca2+ transient. Thus during twitch stimulation BATA did not suppress the Ca2+ transient until the force had been reduced to <50% of its control value. At the same time, the peak myoplasmic free Ca2+ concentration reached during tetanic stimulation was markedly increased, whereas the force was slightly reduced by BAPTA. The effects of BAPTA were not duplicated by using another Ca2+ chelator, EGTA, indicating that BAPTA may act differently as a Ca2+ chelator. Stiffness measurements suggest that the decrease in mechanical performance in the presence of BAPTA is attributable to a reduced number of active cross bridges. The results could mean that BAPTA, under the conditions used, inhibits the binding of Ca2+ to troponin C resulting in a reduced state of activation of the contractile system.

Department of Pharmacology, University of Lund, S-223 62 Lund, Sweden.

0009688591

Am J Physiol 1998 Aug;275(2 Pt 1):C375-81

98349546

Palmer S

Kentish JC

Roles of Ca2+ and crossbridge kinetics in determining the maximum rates of Ca2+ activation and relaxation in rat and guinea pig skinned trabeculae [see comments]

Eng

Actomyosin/*metabolism

Animal

Calcium/*pharmacology/physiology

Comparative Study

Diastole/drug effects/physiology

Egtazic Acid/analogs & derivatives/metabolism/radiation effects

Guinea Pigs

Heart/*drug effects

Ion Transport

Kinetics

Male

Myocardial Contraction/*drug effects

Myocardium/*metabolism

Myofibrils/*drug effects

Photolysis

Rats

Rats, Wistar

Species Specificity

Support, Non-U.S. Gov't

Troponin C/*metabolism

0 (Troponin C)

0 (2-nitrophenyl-EGTA)

67-42-5 (Egtazic Acid)

7440-70-2 (Calcium)

9013-26-7 (Actomyosin)

JOURNAL ARTICLE

19980811

1998 Jul 27

0009-7330

Circ Res

179-86

M

UNITED STATES

2

83

DAJ

Author

199810

We examined the influences of Ca2+ and crossbridge kinetics on the maximum rate of force development during Ca2+ activation of cardiac myofibrils and on the maximum rate of relaxation. Flash photolysis of diazo-2 or nitrophenyl-EGTA was used to produce a sudden decrease or increase, respectively, in [Ca2+] within Triton-skinned trabeculae from rat and guinea pig hearts (22 degrees C). Trabeculae from both species had similar Ca2+ sensitivities, suggesting that the rate of dissociation of Ca2+ from troponin C (k(off)) is similar in the 2 species. However, the rate of relaxation after diazo-2 photolysis was 5 times faster in the rat (16.1 +/- 0.9 s(-1), mean +/- SEM, n = 11) than in the guinea pig (2.99 +/- 0.26 s(-1), n = 7). This indicates that the maximum relaxation rate is limited by crossbridge kinetics rather than by k(off). The maximum rates of rapid activation by Ca2+ after nitrophenyl-EGTA photolysis (k(act)) and of force redevelopment after forcible crossbridge dissociation (k(act)) were similar and were approximately 5-fold faster in rat (k(act)= 14.4 +/- 0.9 s(-1), k(tr)= 13.0 +/- 0.6 s(-1)) than in guinea pig (k(act)= 2.57 +/- 0.14 s(-1), k(tr)= 2.69 +/- 0.30 s(-1)) trabeculae. This too may be mainly due to species differences in crossbridge kinetics. Both k(act) and k(tr) increased as [Ca2+] increased. This Ca2+ dependence of the rates of force development is consistent with current models for the Ca2+ activation of the crossbridge cycle, but these models do not explain the similarity in the maximal rates of activation and relaxation within a given species.

Department of Pharmacology, United Medical and Dental Schools, St. Thomas's Hospital, London, UK.

Comment in: Circ Res 1998 Jul 27;83(2):230-2

0009686757

Circ Res 1998 Jul 27;83(2):179-86

98319626

Walker LA

Gailly P

Jensen PE

Somlyo AV

Somlyo AP

The unimportance of being (protein kinase C) epsilon.

Eng

Animal

Calcium/metabolism

Down-Regulation (Physiology)

Enzyme Inhibitors/pharmacology

Ferrets

Isoenzymes/metabolism/*physiology

Male

Muscle Contraction/drug effects/*physiology

Peptides, Cyclic/pharmacology

Phosphoprotein Phosphatase/antagonists & inhibitors

Portal Vein/enzymology/metabolism

Protein Kinase C/metabolism/*physiology

Support, Non-U.S. Gov't

Support, U.S. Gov't, P.H.S.

EC 2.7.1.- (protein kinase C epsilon)

EC 2.7.1.- (Protein Kinase C)

EC 3.1.3.16 (Phosphoprotein Phosphatase)

EC 3.1.3.53 (myosin-light-chain phosphatase)

0 (Enzyme Inhibitors)

0 (Isoenzymes)

0 (Peptides, Cyclic)

7440-70-2 (Calcium)

77238-39-2 (microcystin)

JOURNAL ARTICLE

PO1 HL48807/HL/NHLBI

19980730

1998 Jul

0892-6638

FASEB J

813-21

M

X

UNITED STATES

10

12

FAS

Author

199810

The purpose of our study was to determine the mechanism through which phorbol esters and smooth muscle myosin phosphatase inhibitors can induce contraction of smooth muscle in the absence of Ca2+. Protein kinase C-epsilon (PKC-epsilon) was previously implicated in this process based largely on its supposed absence in the ferret portal vein, and a correlation was drawn between the presence of this isoform and the ability of smooth muscle to contract independently of Ca2+ and phosphorylation of the 20 kDa regulatory light chains of myosin (MLC20). We demonstrate here, with two antibodies, one to the NH2 terminus and the other to the COOH terminus of PKC-epsilon, that epsilon is present in both ferret portal vein and rabbit portal vein smooth muscle, neither of which exhibits phorbol ester-induced contraction in the absence of Ca2+. However, in the presence of clamped submaximal Ca2+, phorbol es ter increased MLC20 phosphorylation from 17.7+/-1.7% to 46.4+/-3.6% in ferret portal vein smooth muscle and evoked an increase in force. Prolonged (48 h) incubation of ferret portal vein with phorbol esters completely down-regulated PKC-epsilon, as shown by Western blots, and abolished the phorbol ester-evoked contraction at submaximal Ca2+, but not Ca2+-independent, contractions induced by the phosphatase inhibitor microcystin. Contractions induced by microcystin in Ca2+-free solution were associated with increased phosphorylation of myosin light chain kinase (MLCK). Activation of MLCK by autophosphorylation in the absence of Ca2+ occurs in vitro (1). We conclude that PKC-epsilon is neither necessary nor sufficient for Ca2+- independent regulation of myosin II in smooth muscle, but contractions induced by agents that inhibit smooth muscle myosin phosphatase in the absence of Ca2+ may be mediated by MLCK autophosphorylated or activated by another Ca2+-independent kinase.

Department of Molecular Physiology and Biological Physics, University of Virginia, Health Sciences Center, Charlottesville 22906-0011, USA.

0009657521

FASEB J 1998 Jul;12(10):813-21

98297685

Sabido-David C

Brandmeier B

Craik JS

Corrie JE

Trentham DR

Irving M

Steady-state fluorescence polarization studies of the orientation of myosin regulatory light chains in single skeletal muscle fibers using pure isomers of iodoacetamidotetramethylrhodamine.

Eng

Animal

Chickens

Chromatography, High Pressure Liquid

Fluorescence Polarization/methods

Fluorescent Dyes

Gizzard

In Vitro

Muscle Contraction/*physiology

Muscle Fibers/cytology/*physiology

Muscle Relaxation

Muscle, Skeletal/cytology/*physiology

Muscle, Smooth/metabolism

Myosin Light Chains/*analysis

Rabbits

*Rhodamines

Sarcomeres/physiology/ultrastructure

Sensitivity and Specificity

Solutions

Support, Non-U.S. Gov't

0 (Fluorescent Dyes)

0 (Myosin Light Chains)

0 (Rhodamines)

0 (Solutions)

81235-33-8 (tetramethylrhodamine iodoacetamide)

JOURNAL ARTICLE

19980824

1998 Jun

0006-3495

Biophys J

3083-92

M

UNITED STATES

6

74

A5S

Author

199810

The regulatory light chain (RLC) from chicken gizzard myosin was covalently modified on cysteine 108 with either the 5- or 6-isomer of iodoacetamidotetramethylrhodamine (IATR). Labeled RLCs were purified by fast protein liquid chromatography and characterized by reverse-phase high-performance liquid chromatography (HPLC), tryptic digestion, and electrospray mass spectrometry. Labeled RLCs were exchanged into the native myosin heads of single skinned fibers from rabbit psoas muscle, and the ATR dipole orientations were determined by fluorescence polarization. The 5- and 6-ATR dipoles had distinct orientations, and model orientational distributions suggest that they are more than 20 degrees apart in rigor. In the rigor-to-relaxed transition (sarcomere length 2.4 microm, 10 degrees C), the 5-ATR dipole became more perpendicular to the fiber axis, but the 6-ATR dipole became more parallel. This orientation change was absent at sarcomere length 4.0 microm, where overlap between myosin and actin filaments is abolished. When the temperature of relaxed fibers was raised to 30 degrees C, the 6-ATR dipoles became more parallel to the fiber axis and less ordered; when ionic strength was lowered from 160 mM to 20 mM (5 degrees C), the 6-ATR dipoles became more perpendicular to the fiber axis and more ordered. In active contraction (10 degrees C), the orientational distribution of the probe dipoles was similar but not identical to that in relaxation, and was not a linear combination of the orientational distributions in relaxation and rigor.

The Randall Institute, King's College London, England.

0009635762

Biophys J 1998 Jun;74(6):3083-92

98252441

Dekker LR

Rademaker H

Vermeulen JT

Opthof T

Coronel R

Spaan JA

Janse MJ

Cellular uncoupling during ischemia in hypertrophied and failing rabbit ventricular myocardium: effects of preconditioning.

Eng

Animal

Arrhythmia/etiology

Calcium/metabolism

Heart Failure, Congestive/*physiopathology

Heart Hypertrophy/*physiopathology

*Ischemic Preconditioning, Myocardial

Myocardial Ischemia/*physiopathology

Rabbits

Time Factors

7440-70-2 (Calcium)

JOURNAL ARTICLE

19980528

1998 May 5

0009-7322

Circulation

1724-30

A

M

UNITED STATES

17

97

DAW

Author

199807

BACKGROUND: Patients with heart failure show a very high incidence of arrhythmias and sudden death that is often preceded by ischemia; however, data on electrophysiological changes during ischemia in failing myocardium are sparse. We studied electrical uncoupling during ischemia in normal and failing myocardium. METHODS AND RESULTS: Tissue resistance, intracellular Ca2+ concentration (Indo-1 fluorescence ratio), and mechanical activity were simultaneously determined in arterially perfused right ventricular papillary muscles from 11 normal and 15 failing rabbits. Heart failure was induced by combined volume and pressure overload. Before sustained ischemia, muscles were subjected to control perfusion (non-PC) or ischemic preconditioning (PC). The onset of uncoupling during ischemia was equal in non-PC normal (13.6+/-0.9 minutes of ischemia) and non-PC failing hearts (13.3+/-0.7 minutes of ischemia). PC postponed uncoupling in normal hearts by 10 minutes. In failing hearts, however, PC caused a large variability in the onset of uncoupling during ischemia (mean, 12.2+/- 2.1; range, 5 to 22 minutes of ischemia). The duration of uncoupling process was prolonged in failing hearts (12.9+/-0.9 minutes) compared with normal hearts (7.8+/-0.4 minutes). The degree of heart failure and relative heart weight of the failing hearts significantly correlated with the earlier uncoupling after PC and the duration of uncoupling. In every experiment, the start of Ca2+ rise and contracture preceded uncoupling during ischemia. CONCLUSIONS: The duration of the process of ischemia-induced electrical uncoupling in failing hearts is prolonged compared with that in normal hearts. Ischemic PC has detrimental effects in severely failing papillary muscles because it advances the moment of irreversible ischemic damage.

Department of Clinical and Experimental Cardiology, Academic Medical Center, Amsterdam, The Netherlands. LRDekker@AMC.UVA.NL

0009591767

Circulation 1998 May 5;97(17):1724-30

98225225

Wu X

Haystead TA

Nakamoto RK

Somlyo AV

Somlyo AP

Acceleration of myosin light chain dephosphorylation and relaxation of smooth muscle by telokin. Synergism with cyclic nucleotide-activated kinase.

Eng

Animal

Cyclic AMP-Dependent Protein Kinases/*metabolism

Cyclic GMP/analogs & derivatives/pharmacology

Cyclic GMP-Dependent Protein Kinases/*metabolism

Forskolin/pharmacology

In Vitro

Kinetics

Muscle Proteins/genetics/isolation & purification/*pharmacology

Muscle Relaxation

Muscle, Smooth/*drug effects/metabolism/physiology

Myosin-Light-Chain Kinase/*metabolism

Phosphorylation

Rabbits

Recombinant Proteins/genetics/isolation & purification/pharmacology

Sulfhydryl Compounds/metabolism

Support, U.S. Gov't, P.H.S.

EC 2.7.1.117 (Myosin-Light-Chain Kinase)

EC 2.7.10.- (Cyclic AMP-Dependent Protein Kinases)

EC 2.7.10.- (Cyclic GMP-Dependent Protein Kinases)

0 (telokin)

0 (Muscle Proteins)

0 (Recombinant Proteins)

0 (Sulfhydryl Compounds)

31356-94-2 (8-bromocyclic GMP)

66428-89-5 (Forskolin)

7665-99-8 (Cyclic GMP)

JOURNAL ARTICLE

PO1-HL48807/HL/NHLBI

PO1-HL19242/HL/NHLBI

19980602

1998 May 1

0021-9258

J Biol Chem

11362-9

M

X

UNITED STATES

18

273

HIV

Author

199808

Incorporation of 32P into telokin, a smooth muscle-specific, 17-18-kDa, acidic (pI 4.2-4.4) protein, was increased by forskolin (20 microM) in intact rabbit ileum smooth muscle (ileum) and by 8-bromo-cyclic GMP (100 microM) in alpha-toxin-permeabilized ileum. Native telokin (5-20 microM), purified from turkey gizzard, and recombinant rabbit telokin, expressed in Escherichia coli and purified to >90% purity, induced dose- dependent relaxation, associated with a significant decrease in regulatory myosin light chain phosphorylation, without affecting the rate of thiophosphorylation of regulatory myosin light chain of ileum permeabilized with 0.1% Triton X-100. Endogenous telokin was lost from ileum during prolonged permeabilization (>20 min) with 0.1% Triton X- 100, and the time course of loss was correlated with the loss of 8- bromo-cyclic GMP-induced calcium desensitization. Recombinant and native gizzard telokins were phosphorylated, in vitro, by the catalytic subunit of cAMP-dependent protein kinase, cGMP-dependent protein kinase, and p42/44 mitogen-activated protein kinase; the recombinant protein was also phosphorylated by calmodulin-dependent protein kinase II. Exogenous cGMP-dependent protein kinase (0.5 microM) activated by 8- bromo-cyclic GMP (50 microM) phosphorylated recombinant telokin (10 microM) when added concurrently to ileum depleted of its endogenous telokin, and their relaxant effects were mutually potentiated. Forskolin (20 microM) also increased phosphorylation of telokin in intact ileum. We conclude that telokin induces calcium desensitization in smooth muscle by enhancing myosin light chain phosphatase activity, and cGMP- and/or cAMP-dependent phosphorylation of telokin up-regulates its relaxant effect.

Department of Molecular Physiology and Biological Physics, University of Virginia Health Sciences Center, Charlottesville, Virginia 22906- 0011, USA.

0009556631

J Biol Chem 1998 May 1;273(18):11362-9

98260334

Ohizumi Y

Matsunaga K

Nakatani K

Kobayashi J

Potent stimulation of myofilament force and ATPase activity of skeletal muscle by eudistomin M, a novel Ca(++)-sensitizing agent from a Caribbean tunicate.

Eng

Adenosinetriphosphatase/*metabolism

Animal

Calcium/*metabolism

Carbolines/pharmacology

Guinea Pigs

Male

Microfilaments/*drug effects

Muscle, Skeletal/*drug effects

Myosin/analysis

Rabbits

Support, Non-U.S. Gov't

EC 3.6.1.3 (Adenosinetriphosphatase)

0 (Carbolines)

0 (Myosin)

7440-70-2 (Calcium)

88704-39-6 (eudistomin M)

JOURNAL ARTICLE

19980608

1998 May

0022-3565

J Pharmacol Exp Ther

695-9

M

UNITED STATES

2

285

JP3

Author

199808

In the course of our survey of biologically active compounds from natural sources, eudistomins were isolated from a Caribbean tunicate Eudistoma olivaceum. In the present experiments, eudistomin M (Eud-M, > 10(-5) M) caused a concentration-dependent increase in the contractile response of skinned fibers from guinea pig skeletal psoas muscles to Ca++. The superprecipitation and ATPase activity of myosin B from fast skeletal muscles of rabbit back and leg were potentiated by this compound (> 10(-5) M) in a concentration-dependent manner. In skinned fibers, superprecipitation and the ATPase activity of myosin B, Eud-M shifted the concentration-response curve for Ca++ to the upper direction. Ca(++)-, K(+)-EDTA- or Mg(++)-ATPase was not affected by Eud- M. This compound had no effect on the ATPase activity of actomyosin reconstituted from actin and myosin in the presence or absence of troponin. However, the ATPase activity of actin-myosin-troponin- tropomyosin reconstituted system was increased significantly by Eud-M. These results suggest that Eud-M increases the Ca++ sensitivity of the contractile apparatus in skeletal muscles at least partially mediated through troponin-tropomyosin system and thus enhances the ATPase activity of myosin B and the contractile force of myofilament.

Department of Pharmaceutical Molecular Biology, Faculty of Pharmaceutical Sciences, Tohoku University, Sendai, Japan.

0009580615

J Pharmacol Exp Ther 1998 May;285(2):695-9

98204620

Regnier M

Martyn DA

Chase PB

Calcium regulation of tension redevelopment kinetics with 2-deoxy-ATP or low [ATP] in rabbit skeletal muscle.

Eng

Adenosine Triphosphate/*pharmacology

Animal

Biophysics

Calcium/*pharmacology

Deoxyadenine Nucleotides/*pharmacology

In Vitro

Kinetics

Models, Biological

Muscle Contraction/*drug effects/physiology

Myosin ATPase/metabolism

Psoas Muscles/*drug effects/*physiology

Rabbits

Support, U.S. Gov't, P.H.S.

EC 3.6.1.32 (Myosin ATPase)

0 (Deoxyadenine Nucleotides)

1927-31-7 (2'-deoxyadenosine triphosphate)

56-65-5 (Adenosine Triphosphate)

7440-70-2 (Calcium)

JOURNAL ARTICLE

HL52558/HL/NHLBI

HL51277/HL/NHLBI

NS08384/NS/NINDS

19980608

1998 Apr

0006-3495

Biophys J

2005-15

M

UNITED STATES

4

74

A5S

Author

199808

The correlation of acto-myosin ATPase rate with tension redevelopment kinetics (k(tr)) was determined during Ca(+2)-activated contractions of demembranated rabbit psoas muscle fibers; the ATPase rate was either increased or decreased relative to control by substitution of ATP (5.0 mM) with 2-deoxy-ATP (dATP) (5.0 mM) or by lowering [ATP] to 0.5 mM, respectively. The activation dependence of k(tr) and unloaded shortening velocity (Vu) was measured with each substrate. With 5.0 mM ATP, Vu depended linearly on tension (P), whereas k(tr) exhibited a nonlinear dependence on P, being relatively independent of P at submaximum levels and rising steeply at P > 0.6-0.7 of maximum tension (Po). With dATP, Vu was 25% greater than control at Po and was elevated at all P > 0.15Po, whereas Po was unchanged. Furthermore, the Ca(+2) sensitivity of both k(tr) and P increased, such that the dependence of k(tr) on P was not significantly different from control, despite an elevation of Vu and maximal k(tr). In contrast, lowering [ATP] caused a slight (8%) elevation of Po, no change in the Ca(+2) sensitivity of P, and a decrease in Vu at all P. Moreover, k(tr) was decreased relative to control at P > 0.75Po, but was elevated at P < 0.75Po. These data demonstrate that the cross-bridge cycling rate dominates k(tr) at maximum but not submaximum levels of Ca(2+) activation.

Department of Bioengineering, University of Washington, Seattle 98195, USA. mregnier@u.washington.edu

0009545059

Biophys J 1998 Apr;74(4):2005-15

98204590

Uttenweiler D

Weber C

Fink RH

Mathematical modeling and fluorescence imaging to study the Ca2+ turnover in skinned muscle fibers.

Eng

Animal

Biophysics

Caffeine/pharmacology

Calcium/*metabolism

Comparative Study

Fluorescent Dyes

Fura-2

In Vitro

Ion Transport/drug effects

Kinetics

Male

Mathematics

Mice

Mice, Inbred BALB C

*Models, Biological

Muscle Fibers, Fast-Twitch/drug effects/*metabolism

Sarcoplasmic Reticulum/metabolism

Support, Non-U.S. Gov't

0 (Fluorescent Dyes)

58-08-2 (Caffeine)

7440-70-2 (Calcium)

96314-98-6 (Fura-2)

JOURNAL ARTICLE

19980608

1998 Apr

0006-3495

Biophys J

1640-53

M

UNITED STATES

4

74

A5S

Author

199808

A mathematical model was developed for the simulation of the spatial and temporal time course of Ca2+ ion movement in caffeine-induced calcium transients of chemically skinned muscle fiber preparations. Our model assumes cylindrical symmetry and quantifies the radial profile of Ca2+ ion concentration by solving the diffusion equations for Ca2+ ions and various mobile buffers, and the rate equations for Ca2+ buffering (mobile and immobile buffers) and for the release and reuptake of Ca2+ ions by the sarcoplasmic reticulum (SR), with a finite-difference algorithm. The results of the model are compared with caffeine-induced spatial Ca2+ transients obtained from saponin skinned murine fast- twitch fibers by fluorescence photometry and imaging measurements using the ratiometric dye Fura-2. The combination of mathematical modeling and digital image analysis provides a tool for the quantitative description of the total Ca2+ turnover and the different contributions of all interacting processes to the overall Ca2+ transient in skinned muscle fibers. It should thereby strongly improve the usage of skinned fibers as quantitative assay systems for many parameters of the SR and the contractile apparatus helping also to bridge the gap to the intact muscle fiber.

Ruprecht-Karls-Universitat Heidelberg, II Institute of Physiology, Germany.

0009545029

Biophys J 1998 Apr;74(4):1640-53

98151502

Sugi H

Iwamoto H

Akimoto T

Ushitani H

Evidence for the load-dependent mechanical efficiency of individual myosin heads in skeletal muscle fibers activated by laser flash photolysis of caged calcium in the presence of a limited amount of ATP.

Eng

Acetic Acids/*metabolism

Adenosine Diphosphate/metabolism

Adenosine Triphosphate/*metabolism

Animal

Calcium/*metabolism

Chelating Agents

Ethylenediamines/*metabolism

Kinetics

Lasers

Muscle Contraction/*physiology

Muscle Fibers/*physiology/ultrastructure

Muscle, Skeletal/*physiology

Phosphates/metabolism

Photolysis

Rabbits

Solutions

Time Factors

0 (Acetic Acids)

0 (Chelating Agents)

0 (Ethylenediamines)

0 (Phosphates)

0 (Solutions)

117367-86-9 (1-(2-nitro-4,5-dimethoxyphenyl)-N,N,N',N'- tetrakis((oxycarbonyl)methyl)-1,2-ethanediamine)

56-65-5 (Adenosine Triphosphate)

58-64-0 (Adenosine Diphosphate)

7440-70-2 (Calcium)

JOURNAL ARTICLE

19980409

1998 Mar 3

0027-8424

Proc Natl Acad Sci U S A

2273-8

M

X

UNITED STATES

5

95

PV3

Author

199806

Although a contracting muscle regulates its energy output depending on the load imposed on it ("Fenn effect"), the mechanism underlying the load-dependent energy output remains obscure. To explore the possibility that the mechanical efficiency, with which chemical energy derived from ATP hydrolysis is converted into mechanical work, of individual myosin heads changes in a load-dependent manner, we examined the auxotonic shortening of glycerinated rabbit psoas muscle fibers, containing ATP molecules almost equal in number to the myosin heads, after laser-flash photolysis of caged calcium. Immediately before laser- flash activation, almost all of the myosin heads in the fiber are in the state M.ADP.Pi, and can undergo only one ATP hydrolysis cycle after activation. When the fibers were activated to shorten under various auxotonic loads, the length, force, and power output changes were found to be scaled according to the auxotonic load. Both the power and energy outputs were maximal under a moderate auxotonic load. The amount of M.ADP.Pi utilized at a time after activation was estimated from the amount of isometric force developed after interruption of fiber shortening. This amount was minimal in the isometric condition and increased nearly in proportion to the distance of fiber shortening. These results are taken as evidence that the efficiency of chemomechanical energy conversion in individual myosin heads changes in a load-dependent manner.

Department of Physiology, School of Medicine, Teikyo University, Itabashi-ku, Tokyo 173, Japan. sugi@med.teikyo-u.ac.jp

0009482875

Proc Natl Acad Sci U S A 1998 Mar 3;95(5):2273-8

98171004

Horikawa Y

Goel A

Somlyo AP

Somlyo AV

Mitochondrial calcium in relaxed and tetanized myocardium.

Eng

Animal

Calcium/*metabolism/pharmacology

Electric Stimulation

Electron Probe Microanalysis/methods

Freezing

Hamsters

Heart Ventricle

In Vitro

Kinetics

Male

Mitochondria, Heart/*metabolism/ultrastructure

Myocardial Contraction/drug effects/*physiology

Papillary Muscles/drug effects/*physiology/ultrastructure

Rats

Rats, Sprague-Dawley

Ryanodine/pharmacology

Support, U.S. Gov't, P.H.S.

15662-33-6 (Ryanodine)

7440-70-2 (Calcium)

JOURNAL ARTICLE

HL-48807/HL/NHLBI

19980512

1998 Mar

0006-3495

Biophys J

1579-90

M

UNITED STATES

3

74

A5S

Author

199807

The elemental composition of rat cardiac muscle was determined with electron probe x-ray microanalysis (EPMA) of rapidly frozen papillary muscles and trabeculae incubated with ryanodine (1 microM) in either 1.2 or 10 mM [Ca2+]o-containing solutions, paced at 0.6 Hz or tetanized at 10 Hz. Total mitochondrial calcium increased significantly, by 4.2 mmol/kg dry weight during a 7 s tetanus, only in muscles tetanized in the presence of 10 mM [Ca2+]o when cytoplasmic Ca2+ is 1-4 microM (Backx, P. H., W.-D. Gao, M. D. Azan-Backx, and E. Marban. 1995. The relationship between contractile force and intracellular [Ca2+] in intact rat trabeculae. J. Gen. Physiol. 105:1-19). Comparison of total mitochondrial with free mitochondrial Ca2+ reported in the literature indicates that the total/free ratio is approximately 6000 at physiological or near-physiological levels of total mitochondrial calcium. Increases in free mitochondrial [Ca2+] consistent with regulation of mitochondrial enzymes should be associated with increases in total mitochondrial calcium detectable with EPMA. However, such increases in mitochondrial calcium occur only as the result of prolonged, unphysiological elevations of cytosolic [Ca2+].

Department of Molecular Physiology and Biological Physics, University of Virginia Health Sciences Center, Charlottesville 22906-0011, USA.

0009512053

Biophys J 1998 Mar;74(3):1579-90

98170992

Iwamoto H

Thin filament cooperativity as a major determinant of shortening velocity in skeletal muscle fibers.

Eng

Animal

Calcium/metabolism

In Vitro

Isometric Contraction/drug effects/*physiology

Muscle Fibers/drug effects/*physiology/ultrastructure

Muscle, Skeletal/*physiology/ultrastructure

Phosphates/pharmacology

Rabbits

Sarcomeres/drug effects/*physiology/ultrastructure

Support, Non-U.S. Gov't

Time Factors

0 (Phosphates)

7440-70-2 (Calcium)

JOURNAL ARTICLE

19980512

1998 Mar

0006-3495

Biophys J

1452-64

M

UNITED STATES

3

74

A5S

Author

199807

The mechanism underlying the calcium sensitivity of the velocity of shortening of skeletal muscle fibers was investigated using a multiple shortening protocol: within a single contraction, skinned rabbit psoas fibers were made to shorten repetitively under a light load by briefly stretching back to their initial length at regular intervals. At saturating [Ca2+], the initial fast shortening pattern was repeated reproducibly. At submaximal [Ca2+], the first shortening consisted of fast and slow phases, but only the slow phase was observed in later shortenings. When the fibers were held isometric after the first shortening, the velocity of the second shortening recovered with time. The recovery paralleled tension redevelopment, implying a close relationship between the velocity and the number of the preexisting force-producing cross-bridges. However, this parallelism was lost as [Ca2+] was increased. Thus, the velocity was modified in a manner consistent with the cooperative thin filament activation by strong binding cross-bridges and its modulation by calcium. The present results therefore provide evidence that the thin filament cooperativity is primarily responsible for the calcium sensitivity of velocity. The effect of inorganic phosphate to accelerate the slow phase of shortening is also explained in terms of the cooperative activation.

Department of Physiology, School of Medicine, Teikyo University, Tokyo, Japan.

0009512041

Biophys J 1998 Mar;74(3):1452-64

98147195

Dijkman MA

Heslinga JW

Sipkema P

Westerhof N

Perfusion-induced changes in cardiac contractility depend on capillary perfusion.

Eng

Animal

Blood Pressure

Capillaries/*physiology

Coronary Vessels/physiology

Microspheres

*Myocardial Contraction

Oxygen Consumption

Papillary Muscles/anatomy & histology/*physiology

Perfusion

Rats

Rats, Wistar

JOURNAL ARTICLE

19980317

1998 Feb

0002-9513

Am J Physiol

H405-10

M

UNITED STATES

2 Pt 2

274

3U8

Author

199805

The perfusion-induced increase in cardiac contractility (Gregg phenomenon) is especially found in heart preparations that lack adequate coronary autoregulation and thus protection of changes in capillary pressure. We determined in the isolated perfused papillary muscle of the rat whether cardiac muscle contractility is related to capillary perfusion. Oxygen availability of this muscle is independent of internal perfusion, and perfusion may be varied or even stopped without loss of function. Muscles contracted isometrically at 27 degrees C (n = 7). During the control state stepwise increases in perfusion pressure resulted in all muscles in a significant increase in active tension. Muscle diameter always increased with increased perfusion pressure, but muscle segment length was unaffected. Capillary perfusion was then obstructed by plastic microspheres (15 microns). Flow, at a perfusion pressure of 66.6 +/- 26.2 cmH2O, reduced from 17.6 +/- 5.4 microliters/min in the control state to 3.2 +/- 1.3 microliters/min after microspheres. Active tension developed by the muscle in the unperfused condition before microspheres and after microspheres did not differ significantly (-12.8 +/- 29.4% change). After microspheres similar perfusion pressure steps as in control never resulted in an increase in active tension. Even at the two highest perfusion pressures (89.1 +/- 28.4 and 106.5 +/- 31.7 cmH2O) that were applied a significant decrease in active tension was found. We conclude that the Gregg phenomenon is related to capillary perfusion.

Laboratory for Physiology, Vrije Universiteit Amsterdam, The Netherlands.

0009486241

Am J Physiol 1998 Feb;274(2 Pt 2):H405-10

98062941

Blanchard EM

Iizuka K

Christe M

Conner DA

Geisterfer-Lowrance A

Schoen FJ

Maughan DW

Seidman CE

Seidman JG

Targeted ablation of the murine alpha-tropomyosin gene.

Eng

Animal

Gene Targeting

Male

Mice

Mice, Knockout

Myocardium/pathology

Support, Non-U.S. Gov't

Tropomyosin/*genetics/physiology

0 (Tropomyosin)

JOURNAL ARTICLE

19971231

1997 Dec

0009-7330

Circ Res

1005-10

M

UNITED STATES

6

81

DAJ

Author

199803

We created a mouse that lacks a functional alpha-tropomyosin gene using gene targeting in embryonic stem cells and blastocyst-mediated transgenesis. Homozygous alpha-tropomyosin "knockout" mice die between embryonic day 9.5 and 13.5 and lack alpha-tropomyosin mRNA. Heterozygous alpha-tropomyosin knockout mice have approximately 50% as much cardiac alpha-tropomyosin mRNA as wild-type littermates but similar alpha-tropomyosin protein levels. Cardiac gross morphology, histology, and function (assessed by working heart preparations) of heterozygous alpha-tropomyosin knockout and wild-type mice were indistinguishable. Mechanical performance of skinned papillary muscle strips derived from mutant and wild-type hearts also revealed no differences. We conclude that haploinsufficiency of the alpha- tropomyosin gene produces little or no change in cardiac function or structure, whereas total alpha-tropomyosin deficiency is incompatible with life. These findings imply that in heterozygotes there is a regulatory mechanism that maintains the level of myofibrillar tropomyosin despite the reduction in alpha-tropomyosin m>RNA.

Howard Hughes Medical Institute, Boston, Mass., USA.

0009400381

Circ Res 1997 Dec;81(6):1005-10

98042194

Wannenburg T

Janssen PM

Fan D

de Tombe PP

The Frank-Starling mechanism is not mediated by changes in rate of cross-bridge detachment.

Eng

Adenosine Triphosphate/*metabolism

Animal

Calcium/pharmacology

Heart/*physiology

In Vitro

Kinetics

*Models, Cardiovascular

Myocardial Contraction/drug effects/*physiology

Myocardium/metabolism

Myosin ATPase/*metabolism

NAD/metabolism

Rats

Regression Analysis

Sarcomeres/physiology

Support, Non-U.S. Gov't

Support, U.S. Gov't, P.H.S.

EC 3.6.1.32 (Myosin ATPase)

53-84-9 (NAD)

56-65-5 (Adenosine Triphosphate)

7440-70-2 (Calcium)

JOURNAL ARTICLE

HL-52322/HL/NHLBI

HL-03255/HL/NHLBI

19971216

1997 Nov

0002-9513

Am J Physiol

H2428-35

M

UNITED STATES

5 Pt 2

273

3U8

Author

199802

We tested the hypothesis that the Frank-Starling relationship is mediated by changes in the rate of cross-bridge detachment in cardiac muscle. We simultaneously measured isometric force development and the rate of ATP consumption at various levels of Ca2+ activation in skinned rat cardiac trabecular muscles at three sarcomere lengths (2.0, 2.1, and 2.2 microns). The maximum rate of ATP consumption was 1.5 nmol.s- 1.microliter fiber vol-1, which represents an estimated adenosinetriphosphatase (ATPase) rate of approximately 10 s-1 per myosin head at 24 degrees C. The rate of ATP consumption was tightly and linearly coupled to the level of isometric force development, and changes in sarcomere length had no effect on the slope of the force- ATPase relationships. The average slope of the force-ATPase relationships was 15.5 pmol.mN-1.mm-1. These results suggest that the mechanisms that underlie the Frank-Starling relationship in cardiac muscle do not involve changes in the kinetics of the apparent detachment step in the cross-bridge cycle.

Section on Cardiology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27157-1045, USA.

0009374781

Am J Physiol 1997 Nov;273(5 Pt 2):H2428-35

98042192

Janssen PM

de Tombe PP

Protein kinase A does not alter unloaded velocity of sarcomere shortening in skinned rat cardiac trabeculae.

Eng

Animal

Calcium/metabolism

Connective Tissue/*physiology

Cyclic AMP-Dependent Protein Kinases/*pharmacology

Enzyme Inhibitors/pharmacology

Heart/*physiology

In Vitro

Kinetics

Myocardial Contraction

Rats

Rats, Inbred Strains

Receptors, Adrenergic, beta/physiology

Regression Analysis

Sarcomeres/drug effects/*physiology

Support, Non-U.S. Gov't

Support, U.S. Gov't, P.H.S.

Time Factors

EC 2.7.10.- (Cyclic AMP-Dependent Protein Kinases)

0 (Enzyme Inhibitors)

0 (Receptors, Adrenergic, beta)

7440-70-2 (Calcium)

JOURNAL ARTICLE

HL-52322/HL/NHLBI

19971216

1997 Nov

0002-9513

Am J Physiol

H2415-22

M

UNITED STATES

5 Pt 2

273

3U8

Author

199802

Whether beta-adrenergic stimulation affects the cross-bridge cycling rate independently of its effect on Ca2+ handling by the cardiac myocyte is still unknown. An increase in cross-bridge cycling rate may result in increased unloaded velocity of sarcomere shortening (V0). To test this hypothesis directly, skinned rat cardiac trabeculae were attached between a silicon strain gauge (approximately 3.5 kHz resonant frequency) and a fast displacement motor. V0 was measured by a modified "Edman slack test" during a single maximal activation using seven to eight sarcomere-length step releases (measured by laser diffraction) ranging between 0.12 and 0.20 micron (15.0 +/- 0.1 degrees C). beta- Adrenergic stimulation was mimicked by exposing the trabeculae to the catalytic subunit of protein kinase A (PKA). Treatment with PKA (3 micrograms/ml; 45 min) caused a significant (P < 0.01) increase (41 +/- 13%) in the Ca2+ concentration required for half-maximal steady-state tension development. Neither maximum tension nor V0 was affected by treatment with PKA, suggesting that beta-adrenergic stimulation does not affect the rate-limiting step of cross-bridge cycling during unloaded shortening in myocardium.

Department of Physiology and Biophysics, University of Illinois at Chicago 60607-7171, USA.

0009374779

Am J Physiol 1997 Nov;273(5 Pt 2):H2415-22

97460444

Wier WG

ter Keurs HE

Marban E

Gao WD

Balke CW

Ca2+ 'sparks' and waves in intact ventricular muscle resolved by confocal imaging [see comments] [published erratum appears in Circ Res 1997 Nov;81(5):893]

Eng

Aniline Compounds

Animal

Calcium/*metabolism

Fluorescent Dyes

Heart Ventricle

Microscopy, Confocal

Myocardial Contraction

Myocardium/*metabolism

Rats

Rats, Inbred BN

Support, Non-U.S. Gov't

Support, U.S. Gov't, P.H.S.

Ventricular Function

Xanthenes

0 (Aniline Compounds)

0 (Fluorescent Dyes)

0 (Xanthenes)

121714-13-4 (Fluo-3)

7440-70-2 (Calcium)

JOURNAL ARTICLE

HL-02466/HL/NHLBI

HL-29473/HL/NHLBI

HL-50435/HL/NHLBI

+

19971030

1997 Oct

0009-7330

Circ Res

462-9

M

UNITED STATES

4

81

DAJ

Author

199801

The [Ca2+]i transient in heart is now thought to involve the recruitment and summation of discrete and independent "units" of Ca2+ release (Ca2+ "sparks") from the sarcoplasmic reticulum, each of which is controlled locally by single coassociated L-type Ca2+ channels ("local control theory of excitation-contraction coupling"). All prior studies on Ca2+ sparks, however, have been performed in single enzymatically dissociated heart cells under nonphysiological conditions. In order to understand the possible significance of Ca2+ sparks to normal working cardiac muscle, we used confocal microscopy to record Ca2+ sparks, spatially averaged [Ca2+]i transients and Ca2+ waves in individual cells of intact rat right ventricular trabeculae (composed of < 15 cells in cross section) microinjected with the Ca2+ indicator fluo 3 under physiological conditions ([Ca2+]o, 1 mmol/L; temperature, 33 +/- 1 degree C). Twitch force was recorded simultaneously. When stretched to optimal length (sarcomere length, 2.2 microns) and stimulated at 0.2 Hz, the trabeculae generated approximately equal to 700 micrograms of force per cell. Spatially averaged [Ca2+]i transients recorded from individual cells within a trabecula were similar to those recorded previously from single cells. The amplitude distribution of the peak ratio of Ca2+ sparks was bimodal, with maxima at ratios of 1.8 +/- 0.3 and 2.7 +/- 0.2 (mean +/- SD), respectively. The amplitude of the peak of Ca2+ sparks was approximately equal to 170 nmol/L. Ca2+ sparks occurred at a frequency of 12.0 +/- 0.8/s (mean +/- SEM) in line scans covering 94 sarcomeres. Ca2+ waves occurred randomly at a frequency of 0.57 +/- 0.08/s and propagated with a velocity of 29.5 +/- 1.7 microns/s. The extent of Ca2+ wave propagation was 3.9 +/- 0.3 sarcomere lengths (sarcomere length, 2.2 microns). Ca2+ sparks could be identified along the leading edge of the waves at intervals of 1.30 +/- 0.11 sarcomere length. Our observations suggest that (1) Ca2+ sparks, similar to those recorded in single cells, occur in trabeculae under physiological conditions and (2) coupling of Ca2+ spark generation between neighboring sites occurs and may lead to (3) the development of Ca2+ waves, which propagate under physiological conditions at a low velocity over limited distances. The results suggest that concepts of excitation-contraction coupling recently derived from isolated myocytes are applicable to intact cardiac trabeculae [corrected].

Department of Physiology, University of Maryland School of Medicine, Baltimore 21201, USA. gwier001@umabnet.ab.umd.edu