AJP - Endocrinology and Metabolism, Vol 238, Issue 2 87-E95, Copyright © 1980 by American Physiological Society
Regulation of calcium fluxes in pancreatic islets: two calcium movements' dissociated response to glucose
A. Herchuelz and W. J. Malaisse
At normal extracellular 40Ca concentration (1.0--1.5 mM), D-glucose
initially reduces and subsequently increases 45Ca efflux from prelabeled
rat pancreatic islets, whether in the absence or presence of 20 mM Ca-EGTA.
Thus, the initial fall cannot be attributed to a reuptake of effluent 45Ca.
Both the fall and rise in effluent 45Ca represent sustained and rapidly
reversible phenomena partially masked by one another. The dose-action
relationship for the initial fall in 45Ca efflux (Km = 4.2 mM) differs
vastly from that characterizing the secondary rise in 45Ca efflux (Km = 9.1
mM). Mannoheptulose, iodoacetate, and low temperature inhibit both the
early fall and secondary rise in effluent radioactivity normally evoked by
glucose. D-Glucose (8.3 mM) and D-glyceraldehyde (10 mM) exert comparable
effects on 45Ca efflux. The initial fall and later increase in 45Ca efflux
evoked by glucose, although dependent on the integrity of glucose
metabolism, correspond to two distinct processes in the rapid regulation of
Ca handling by the islet cells.
