REGULATION OF NA+/CA2+ EXCHANGE IN THE RAT PANCREATIC B-CELL

Na+/Ca2+ exchange in the B cell was recently characterized by measuring intracellular-Na+-dependent Ca-45(2+) uptake in isolated rat pancreatic islet cells. The aim of the present study was to investigate the regulation of this process. Extracellular pH (pH(o)) and intracellular pH (pH(i)) markedly affected Na+/Ca2+ exchange. A fall of 0.04 unit in pH(i) decreased the exchange by 45 %, whereas a rise of 0.13 unit increased the uptake by 70 %. Mitochondrial poisons (oligomycin, antimycin A and 2,4-dinitrophenol) inhibited reverse Na+/Ca2+ exchange by about 25-50 %. The exchanger displayed a low Q10 (temperature coefficient), indicating that it is only indirectly dependent on metabolic energy. The phorbol ester phorbol 12-myristate 13-acetate did not affect Na+/Ca2+ exchange. Likewise, lowering the extracellular K+ concentration did not inhibit Ca-45(2+) uptake. In conclusion, the pH(i) and the metabolic state of the cell may represent important modulatory signals by which insulin secretagogues such as glucose could regulate reverse Na+/Ca2+ exchange in the B cell. The process does not appear to co-transport K+ nor to be influenced by protein kinase C.