The inhibition of rabbit skeletal muscle contraction by hydrogen ions and phosphate.

Abstract

SUMMARY1. 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 Ca21 (pCa 4-5) at 10 '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 (P0) 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-' myosin head-' (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 Vma. 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 t To whom correspondence should be addressed.

Effects of stimulation frequency versus pulse duration modulation on muscle fatigue

“…3c). This overshoot of force may have caused greater metabolic energy expenditure (Boska, 1994;Potma et al, 1994;Stienen et al, 1995), and produced greater muscle fatigue (Cooke et al, 1988;Sahlin et al, 1998;Westerblad et al, 1998) than would have been produced if the targeted force was not exceeded. A better strategy would have been to only increase the stimulation frequency or pulse-duration to the level needed to produce the targeted force with minimal overshoot.…”

Anaerobic energy production and O2 deficit‐debt relationship during exhaustive exercise in humans.

“…It is of note that the lactate release is of equal magnitude at 3-4 and 7-8 min at 50 W. The magnitude of the anaerobic contribution is a minimum value as some accumulation of lactate may also occur at the 'steady-state' phase at this exercise intensity. The possibility exists that this anaerobic energy yield from glycolysis compensates for a reduction in free energy (AG) from ATP hydrolysis when increases take place in factors such as temperature and Pi and reduction in pH (Kawai, Guth, Winnikes, Haist & Ruegg, 1987; Cooke, Franks, Luciani & Pate, 1988). If this assumption is correct, one would have anticipated that the same would occur during the intense exercise, i.e.…”

Coexistence of potentiation and fatigue in skeletal muscle

“…These factors include mainly decreased pH and increased inorganic phosphate concentration. Skinned fiber experiments conducted at room temperature (or colder) have been done to confirm this effect (25)(26)(27). However, the impact of acidosis on the contractile response D.E.…”