Muscle contraction and calcium ion

Abstract

The mechanism of action of calcium ion on the troponin-tropomyosin-actin system was briefly reviewed. Direct action of calcium on myosin was discussed, and throught to be not important in physiological control of contraction and relaxation. Mechanical properties, such as maximum shortening velocity, length-tension relation, rate of tension development etc., of skinned muscle fibers partially activated by calcium were described, which are still to be explained on a molecular basis.The mechanism of uptake of calcium by the sarcoplasmic reticulum (SR) was briefly reviewed. Calcium releasing action of calcium ion itself and that of "depolarization" of the SR were described. Calcium ion itself was shown to be not playing an essential role in phyiological excitation-contraction coupling of skeletal muscle. Recent progress in excitation-contraction coupling other than that with skinned fibers was briefly reviewed.