Length Dependence of Activation of Skinned Muscle Fibers by Calcium

It is well known that the active tetanic tension of a living skeletal muscle fiber decreases linearly with increase of fiber length beyond its slack length (Ramsey and Street, 1940; Gordon et al., 1966). Skinned skeletal muscle fibers also behave similarly at high concentrations of calcium (Hellam and Podolsky, 1969). This has been successfully attributed to the decreased number of interacting sites between thick (myosin-containing) and thin (actin-containing) filaments on the basis of the sliding filament theory of contraction (Gordon et al,, 1966). On the other hand, the activation of skeletal muscle fiber seems to be increased by stretch, as indicated by the following facts. First, the active