Effects of calcium and ionic strength on shortening velocity and tension development in frog skinned muscle fibres.

Publisher Website
Google Scholar
Abstract
The influence of Ca2+ concentration and ionic strength on the maximum velocity or shortening (Vmax) and the tension generating capability of frog skinned muscle fibers has been studied at temperatures between 1-10.degree. C. Fiber segments were mounted between a force transducer and servo motor, where they could be viewed and photographed through a microscope. Segments in which the striations became non-uniform during activation were discarded. Velocity was obtained as a function of load by stepping the tension to values less than the steady isometric tension. Vmax was then determined by an extrapolation technique. Vmax was obtained using a 2nd, independent method by measuring the times required to take up various amounts of slack imposed on the segments. Vmax was significantly influenced by the Ca2+ concentration, decreasing by about 1/2 when the Ca2+ concentration was reduced to give steady tensions less than half-maximal. Vmax was not influenced by changes in ionic strength, in the range 0.09-0.18 M. Steady tension increased as ionic strength was decreased in the same range. Apparently, the effect of changes in ionic strength is to alter the numbers or stiffness of attached cross-bridges, while there is no apparent influence of ionic strength on the steady-state kinetics of the actin-myosin interaction during unloaded shortening. The mechanism responsible for the influence of Ca2+ on Vmax is unknown, though possible sites of action for Ca2+ are discussed.