Molecular step(s) of force generation: temperature-perturbation experiments on muscle fibres.
The steady active muscle force is reduced, but the force generation induced by a standard temperature jump becomes 2-3 fold faster with increased inorganic phosphate level, [Pi]. The increase in the rate of force generation also exhibits saturation at higher [Pi] levels and the relation is hyperbolic. These observations are consistent with a kinetic scheme where rapid Pi release by actomyosin crossbridges in muscle is preceded by the force generation step. Such a scheme accounts for the sigmoidal temperature dependence of steady active force and its sensitivity to [Pi]. The [Pi] dependence of force recovery after stretch (positive strain) is also hyperbolic, suggesting that the "pre Pi-release force generation step" is strain-sensitive--as expected. However, length-release (negative strain) force transients are not [Pi] sensitive indicating an asymmetry, but its significance and also the kinetic step underlying force recovery from negative strain remain unclear.
Ranatunga
K W
KW
Muscle Contraction Group, Department of Physiology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
Coupland
M E
ME
D000205:Actomyosin / Q000737:chemistry; D000818:Animals; D001831:Body Temperature; D004305:Dose-Response Relationship, Drug; D007537:Isometric Contraction; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000502:physiology*; D016658:Psoas Muscles / Q000502:physiology*; D011817:Rabbits; D013696:Temperature; D013997:Time Factors
D000205:Actomyosin