A FLUOROMETRIC AND AMPEROMETRIC STUDY OF CALCIUM AND SECRETION IN ISOLATED MOUSE PANCREATIC BETA-CELLS

We have examined the temporal relationship between intracellular Ca2concentration ([Ca2+](i)) and secretion in single intact pancreatic be ta-cells. secretion was detected as the release of 5-hydroxytryptamine from pre-loaded beta-cells, using amperometry, and changes in [Ca2+]( i) were monitored by microfluorimetry. Stimulation of beta-cells by el evation of the extracellular K+ concentration ([K+](o)), acetylcholine or glucose increased [Ca2+](i) and, after a delay of 2-7 s, evoked am perometric currents. In the presence of glucose, we observed oscillati ons in [Ca2+](i) which were associated with oscillations in the amplit ude and frequency of amperometric currents: however, the temporal corr elation was not exact, suggesting that there is a significant latency between the increase in average [Ca2+](i) and exocytosis. Both the amp litude and frequency of the amperometric currents elicited by 50 mM KC l declined with successive stimulation, but were restored by agents wh ich elevate intracellular adenosine 3':5':cyclic monophosphate (cAMP). This suggests that beta-cells may possess a readily releasable pool o f granules which is replenished by cAMP. The variable amplitude of the amperometric currents is discussed in terms of a model in which sever al secretory granules fuse simultaneously with the plasma membrane.