Calcium transients in mammalian ventricular muscle.

Abstract

The calcium-sensitive photoprotein aequorin was microinjected into cells of rat and cat ventricular muscle. During subsequent stimulation of the muscle light emission could be detected and this signal is a function of the intracellular [Ca++]. The time course and amplitude of the intracellular [Ca++] transient occurring during contraction is described. The effects on tension and light emission of changing external [Ca++] and stimulus frequency and of adding adrenaline and caffeine to the bathing solution are described. These results show that changes in external calcium and stimulus frequency alter tension by means of changes in the intracellular [Ca++] whereas adrenaline in addition alters the sensitivity of the contractile system to intracellular [Ca++]. The results also suggest that although a fall in intracellular [Ca++] always precedes relaxation, the time course of the fall of [Ca++] is not generally a rate limiting step in the lime course of relaxation.