Calcium Movements in Muscle

Abstract

The movements of calcium in muscle have been followed during contraction and contracture to test the hypothesis that the release of calcium from the surface of the muscle membrane during stimulation initiates the contractile mechanism. Nitrate ion increases the calcium influx during a single twitch and during potassium contracture, and also increases the tension developed. The increased entry of calcium during a potassium contracture is transient and not sustained as is the contracture. Caffeine, which brings about a contracture without depolarization of the membrane and despite the absence of calcium from the medium, causes calcium to be released from the muscle.