ACTIVIN-A INCREASES INTRACELLULAR FREE CALCIUM CONCENTRATIONS IN RAT PANCREATIC-ISLETS

Activin A stimulated insulin secretion in rat pancreatic islets, an ef fect that was attenuated by reduction of extracellular Ca2+ and abolis hed by either nitrendipine or verapamil. Activin A increased intracell ular the free Ca2+ concentration, [Ca2+]i in fura-2-loaded islets. Act ivin A-mediated elevation of [Ca2+]i was abolished by the reduction of extracellular Ca2+ or the addition of nifedipine. In addition, activi n A did not increase [Ca2+]i in the presence of diazoxide, an opener o f ATP-sensitive K+ channels. These results suggest that activin A incr eases insulin secretion by stimulating Ca2+ entry.