SINGLE CELL ASSAY OF EXOCYTOSIS FROM PANCREATIC-ISLET B-CELLS

We have measured changes in membrane capacitance (DELTA-C(m)) in pancreatic B cells as a single cell assay of insulin secretion. Evidence that depolarization evoked DELTA-C(m) reflects exocytosis includes it's voltage, temperature and Ca2+o dependence. Decreases in C(m) presumably reflecting endocytosis, occur on a variable time scale. Two features that make B cells unique among excitable cells are the large magnitude of DELTA-C(m), 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.