Single cell assay of exocytosis from pancreatic islet B cells

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Abstract
We have measured changes in membrane capacitance (ΔCm) in pancreatic B cells as a single cell assay of insulin secretion. Evidence that depolarization evoked ΔCm reflects exocytosis includes it's voltage, temperature and Ca2+ o dependence. Decreases in Cm, presumably reflecting endocytosis, occur on a variable time scale. Two features that make B cells unique among excitable cells are the large magnitude of ΔCm, when normalized to Ca2+ current, and the rapid “fatigue” of the response for even minimal stimulation, perhaps due to the depletion of a readily releasable pool of vesicles.