The inhibition of rabbit skeletal muscle contraction by hydrogen ions and phosphate.
- 1 January 1988
- journal article
- research article
- Published by Wiley in The Journal of Physiology
- Vol. 395 (1), 77-97
- https://doi.org/10.1113/jphysiol.1988.sp016909
Abstract
1. The effects of phosphate and protons on the mechanics and energetics of muscle contraction have been investigated using glycerinated rabbit psoas muscle. 2. Fibres were fully activated by addition of Ca2+ (pCa 4-5) at 10.degree. C. The velocities of contraction were measured in isotonic load clamps, and the velocities of unloaded fibres were measured by applying a series of step changes in fibre length. Fibre ATPase activity was monitored using an enzyme system to couple ADP production to reduced nicotinamide-adenine dinucleotide (NADH) and measuring the depletion of NADH by optical density. 3. At pH 7.0 and 3 mM-phosphate, isometric tension (Po) was 13.2 .+-. 0.9 N/cm2 (mean .+-. S.E.M., n = 10 observations), the maximum contraction velocity (Vmax) was 1.63 .+-. 0.05 lengths/s (n = 5) and the ATPase activity was 1.27 .+-. 0.12 s-1 myosin head-1 (n = 35). Increasing phosphate from 3 to 20 mM at pH 7.0 does not affect Vmax, causes a small decrease in the ATPase activity (15-20%) and decreases Po by approximately 20%. Changing pH from 7 to 6 at 3 mM-phosphate decreases Po by 45% and both Vmax and ATPase activity by 25-30%. The effects of changing both pH and phosphate were approximately additive for all parameters measured. The inhibition of these parameters by low pH and high concentration of phosphate was reversible. 4. The force-velocity relation was fitted by the Hill equation using a non-linear least-squares method. The value of the parameter which describes the curvature, a/Po, was 0.20. The curvature of the force-velocity relation was not changed by addition of phosphate or by changes in pH. 5. These data provide information on both the kinetics of the actomyosin interaction and on the process of muscle fatigue. The data are consistent with models of cross-bridge kinetics in which phosphate is released within the powerstroke in a step involving a rapid equilibrium between states. The inhibition by protons is more complex, and may involve less specific effects on protein structure. 6. During moderate fatigue of living skeletal muscle, MgATP concentration is known to remain approximately constant at 4 mM, phosphate to increase from 3 to 20 mM, and protons from 0.1 to 1 .mu.M. The data suggest that much of the inhibition of Po observed during moderate fatigue can be explained by the increased levels of phosphate and protons, and that much of the inhibition of fibre Vmax and ATPase activity can be explained by the increase in protons.This publication has 47 references indexed in Scilit:
- The role of orthophosphate in crossbridge kinetics in chemically skinned rabbit psoas fibres as detected with sinusoidal and step length alterationsJournal of Muscle Research and Cell Motility, 1986
- Influence of partial activation on force-velocity properties of frog skinned muscle fibers in millimolar magnesium ion.The Journal of general physiology, 1986
- Inhibition of myofibrillar and actomyosin subfragment 1 adenosine triphosphatase by adenosine 5'-diphosphate, pyrophosphate and adenyl-5'-yl imidodiphosphateBiochemistry, 1986
- The necessity of using two parameters to describe isotonic shortening velocity of muscle tissues: the effect of various interventions upon initial shortening velocity (vi) and curvature (b)Basic Research in Cardiology, 1986
- Correlated reduction of velocity of shortening and the rate of energy utilization in mouse fast-twitch muscle during a continuous tetanus.The Journal of general physiology, 1983
- Vanadare and phosphate ions reduce tension and increase cross-bridge kinetics in chemically skinned heart muscleBiochimica et Biophysica Acta (BBA) - General Subjects, 1981
- Metabolic correlates of fatigue and of recovery from fatigue in single frog muscle fibers.The Journal of general physiology, 1978
- Muscular fatigue investigated by phosphorus nuclear magnetic resonanceNature, 1978
- A Rapid and Sensitive Method for the Quantitation of Microgram Quantities of Protein Utilizing the Principle of Protein-Dye BindingAnalytical Biochemistry, 1976
- Phosphate Starvation and the Nonlinear Dynamics of Insect Fibrillar Flight MuscleThe Journal of general physiology, 1972