Abstract
Perifusion of rat pancreatic islets with a physiologic, 6-mM amino acid mixture resulted in typical acute and second phase glucagon secretion over 30 min. At various intervals, islets were acutely fixed and processed for scanning electron microscopy, identification of alpha cells, and measurements of single alpha cell content of calcium (Ca), potassium (K) and sodium (Na) with energy-dispersive x-ray analysis. Biphasic glucagon secretion was attended by corresponding biphasic Ca accumulation and a reciprocal, biphasic suppression of K content and acute phase suppression of Na in alpha cells. All secretory and cellular events were preceded by an evanescent upward spike in alpha cell K at 1 min. These results indicate that alpha cell glucagon secretion in response to amino acid mixtures may be initiated by a K signal and is coupled subsequently to phasic changes in alpha cell Ca content. Fluctuations of alpha cell K and Na appear to relate inversely to Ca, suggesting that transmembrane fluxes of the three cations are interrelated.
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