The effect of the reciprocal relationship of Ca2+ and cAMP on the control of beating in cultured rat heart cells.

The demonstration of Ca2+ control of the cAMP level in heart cells and the localization of the Ca2+ activator protein of cAMP phosphodiesterase on the sarcoplasmic reticulum (SR) have led us to postulate a model whereby the Ca2+ flux is related to the cAMP flux. The model suggests that the increase in cytosol Ca2+ automatically results in an increase in SR Ca2+ and a subsequent decrease in cAMP to allow for the periodic flux of Ca2+ and cAMP in the contraction cycle.