Activin A increases intracellular free calcium concentrations in rat pancreatic islets

Activin A stimulated insulin secretion in rat pancreatic islets, an effect that was attenuated by reduction of extracellular Ca2+ and abolished by either nitrendipine or verapamil. Activin A increased intracellular the free Ca2+ concentration, [Ca2+]i in fura-2-loaded islets. Activin A-mediated elevation of [Ca2+]i was abolished by the reduction of extracellular Ca2+ or the addition of nifedipine. In addition, activin A did not increase [Ca2+]i in the presence of diazoxide, an opener of ATP-sensitive K+ channels. These results suggest that activin A increases insulin secretion by stimulating Ca2+ entry.