Effects of MgATP and MgADP on the cross-bridge kinetics of rabbit soleus slow-twitch muscle fibers

Gang Wang; Masataka Kawai

doi:10.1016/S0006-3495(96)79346-3

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Effects of MgATP and MgADP on the cross-bridge kinetics of rabbit soleus slow-twitch muscle fibers

Journal article

Open access

Peer reviewed

Effects of MgATP and MgADP on the cross-bridge kinetics of rabbit soleus slow-twitch muscle fibers

Gang Wang and Masataka Kawai

Biophysical journal, Vol.71(3), pp.1450-1461

09/1996

DOI: 10.1016/S0006-3495(96)79346-3

PMCID: PMC1233612

PMID: 8874019

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Abstract

The elementary steps surrounding the nucleotide binding step in the cross-bridge cycle were investigated with sinusoidal analysis in rabbit soleus slow-twitch muscle fibers. The single-fiber preparations were activated at pCa 4.40, ionic strength 180 mM, 20 degrees C, and the effects of MgATP (S) and MgADP (D) concentrations on three exponential processes B, C, and D were studied. Our results demonstrate that all apparent (measured) rate constants increased and saturated hyperbolically as the MgATP concentration was increased. These results are consistent with the following cross-bridge scheme: [cross-bridge scheme: see text] where A = actin, M = myosin, S = MgATP, and D = MgADP. AM+S is a collision complex, and AM*S is its isomerized form. From our studies, we obtained K0 = 18 +/- 4 mM-1 (MgADP association constant, N = 7, average +/- sem), K1a = 1.2 +/- 0.3 mM-1 (MgATP association constant, N = 8 hereafter), k1b = 90 +/- 20 s-1 (rate constant of ATP isomerization), k-1b = 100 +/- 9 s-1 (rate constant of reverse isomerization), K1b = 1.0 +/- 0.2 (equilibrium constant of isomerization), k2 = 21 +/- 3 s-1 (rate constant of cross-bridge detachment), k-2 = 14.1 +/- 1.0 s-1 (rate constant of reversal of detachment), and K2 = 1.6 +/- 0.3 (equilibrium constant of detachment). K0 is 8 times and K1a is 2.2 times those in rabbit psoas, indicating that nucleotides bind to cross-bridges more tightly in soleus slow-twitch muscle fibers than in psoas fast-twitch muscle fibers. These results indicate that cross-bridges of slow-twitch fibers are more resistant to ATP depletion than those of fast-twitch fibers. The rate constants of ATP isomerization and cross-bridge detachment steps are, in general, one-tenth to one-thirtieth of those in psoas.

Biophysics

Energy Metabolism

Muscle Fibers, Fast-Twitch - drug effects

Isometric Contraction - drug effects

Muscle Fibers, Fast-Twitch - metabolism

Muscle, Skeletal - metabolism

Muscle Fibers, Slow-Twitch - metabolism

Muscle Fibers, Slow-Twitch - drug effects

Adenosine Triphosphate - biosynthesis

Adenosine Triphosphate - pharmacology

Muscle Fibers, Fast-Twitch - chemistry

Adenosine Triphosphate - metabolism

Muscle, Skeletal - chemistry

Muscle, Skeletal - drug effects

Myocardium - metabolism

Muscle Fibers, Slow-Twitch - chemistry

Binding Sites

Muscle Fatigue

Isometric Contraction - physiology

Rabbits

Biophysical Phenomena

Adenosine Diphosphate - pharmacology

Animals

Creatine Kinase - metabolism

Adenosine Diphosphate - metabolism

Kinetics

In Vitro Techniques

Details

Title: Subtitle: Effects of MgATP and MgADP on the cross-bridge kinetics of rabbit soleus slow-twitch muscle fibers
Creators: Gang Wang - Department of Anatomy, University of Iowa, Iowa City 52242, USA
Masataka Kawai
Resource Type: Journal article
Publication Details: Biophysical journal, Vol.71(3), pp.1450-1461
Publisher: United States
DOI: 10.1016/S0006-3495(96)79346-3
PMID: 8874019
PMCID: PMC1233612
ISSN: 0006-3495
eISSN: 1542-0086
Language: English
Date published: 09/1996
Academic Unit: Anatomy and Cell Biology; Internal Medicine
Record Identifier: 9984025587102771

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