Insulin-specific receptor-mediated slowing of beat rate in embryonic heart cells.

Spheroidal aggregates of embryonic heart cells showed their spontaneous beat rate when exposed to insulin. The concentration that produced a half-maximal response (1.7 nM) corresponded to the dissociation constant of binding to a specific high-affinity insulin receptor. The pace-maker phase of action potentials recorded during insulin perfusion was preceded by a prolonged or flattened after hyperpolarization, and its slope was less steep than controls. The action potential duration was also prolonged. These results indicate that physiological concentrations of insulin can regulate the embryonic heart rate.