CHARACTERIZATION OF THE PROCESS OF SODIUM-CALCIUM EXCHANGE IN PANCREATIC-ISLET CELLS

Na+ -Ca2+ exchange may play a role in Ca2+ extrusion from the pancreatic B-cell. The characteristics of the process working in its reverse mode were examined in normal rat pancreatic islet cells. Isosmotical replacement of extracellular Na+ by sucrose induced a concentration-dependent increase in Ca-45 uptake, displaying a pharmacological sensitivity compatible with an uptake mediated by Na+ -Ca2+ exchange. Glucose, up to 2.8 mM, stimulated reverse Na+ -Ca2+ exchange. Likewise, membrane depolarization activated the process but only under raised intracellular Na+ activity. In conclusion, the B-cell Na+ -Ca2+ exchange displays properties similar to those observed in other cells: reversibility and sensitivity to membrane potential. When working in its reverse mode the exchanger displays a quite large capacity. The role played by the exchanger in the process of insulin release warrants further investigation.