Model for the Action of Calcium in Muscle

CALCIUM ions play an important part in contraction^1–3, but little is known of the way that changes in internal calcium actually control the events that lead to the development of tension. Most experiments involving calcium have been performed under steady state conditions at different stabilized calcium concentrations^4–9 and can only give limited information as to the action of calcium. Recently, tension transient experiments have been described at either constant calcium concentration^6,7 or when the calcium concentration was varying in a known manner^10,11. From these and related experiments, a model for the kinetics of calcium has been deduced which predicts not only the time course of tension development from just a knowledge of the free calcium concentration, but which is also able to correlate the ATPase, tension and calcium binding responses in the steady state. The model considers that two calciums act as separate effectors with a de-repressant action in the same functional unit.