INSULIN EXOCYTOSIS AND GLUCOSE-MEDIATED INCREASE IN CYTOPLASMIC FREE CA2-CELL ARE INDEPENDENT OF CYCLIC ADP-RIBOSE( CONCENTRATION IN THE PANCREATIC BETA)

Stimulation of pancreatic P-cells by glucose gives rise to an increase in the cytoplasmic free calcium concentration ([Ca2+](i)) and exocyto sis of insulin. Cyclic adenosine 5'-diphosphate ribose (cADPR), a meta bolite of beta-NAD(+), has been reported to increase [Ca2+](i) in panc reatic beta-cells by releasing Ca2+ from inositol 1,4,5-trisphosphate- insensitive intracellular stores. In the present study, we have examin ed the role of cADPR in glucose-mediated increases in [Ca2+](i) and in sulin exocytosis. Dispersed ob/ob mouse beta-cell aggregates were eith er pressure microinjected with fura-2 salt or loaded with fura-2 aceto xymethyl ester, and [Ca2+](i) was monitored by microfluorimetry. Micro injection of beta-NAD(+) into fura-2-loaded beta-cells did not increas e [Ca2+](i) nor did it alter the cells' subsequent [Ca2+](i) response to glucose. Cells microinjected with the cADPR antagonist 8NH(2)-cADPR increased [Ca2+](i) in response to glucose equally well as those inje cted with cADPR. Finally, the ability of cADPR to promote exocytosis o f insulin ill electropermeabilized beta-cells was investigated. cADPR on its own did not increase insulin secretion nor did it potentiate Ca 2+-induced insulin secretion. We conclude that cADPR neither plays a s ignificance role in glucose-mediated increases in [Ca2+](i) nor intera cts directly with the molecular mechanisms regulating exocytosis of in sulin in normal pancreatic beta-cells.