Fiber type-dependent differences in rates of cross-bridge transitions, modulated by calcium sensitivity and myosin isoform content, may account for the characteristic rates of tension development in mammalian fast and slow skeletal muscles.
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May explain fiber-type differences in skeletal muscle tension development; leaves open translation to cardiac physiology or clinical settings.
The fundamental mechanism underlying the differing rates of tension development in fast and slow mammalian skeletal muscle is still unknown. Now, in skinned (membrane-permeabilized) single fibers it has been shown that the rate of formation of the strongly bound, force-producing cross-bridge between actin and myosin is calcium-sensitive in both fast and slow fibers and that the rate is markedly greater in fast fibers. The transition rates obtained at high calcium concentrations correlated with myosin isoform content, whereas at low calcium concentrations the thin filament regulatory proteins appeared to modulate the rate of tension development, especially in fast fibers. Fiber type-dependent differences in rates of cross-bridge transitions may account for the characteristic rates of tension development in mammalian fast and slow skeletal muscles.
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Metzger et al. (1990) studied this question.
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