Intracellular Localization of Calcium in Pancreatic B Cells in Relation to Insulin Secretion by the Perfused ob/ob Mouse Pancreas*

Abstract

Changes in the distribution of intracellular calcium in B-cells from the perfused ob/ob mouse pancreas in relation to the secretory state of the B-cell were followed using the pyroantimonate technique for calcium precipitation. At the internal surface of the B-cell membrane a highly mobile reservoir of calcium was mobilized during the first 1-3 min of stimulation of the B-cells by glucose as well as by tolbutamide resulting in an increased calcium precipitation in the cytoplasma. During prolonged stimulation of insulin secretion by glucose the calcium precipitation along the internal surface of the B-cell membrane was restored. Concomitantly calcium deposits in the secretory granules and to a lesser extend in the mitochondria increased. Tolbutamide neither restored the membrane-bound pool nor increased the calcium uptake of the secretory granules but decreased mitochondrial calcium. It suggests that this cytoplasmic increase of calcium primarily results from intracellular redistribution.