Calcium and pancreatic β-cell function: 6. glucose and intracellular 45Ca distribution

Abstract Glucose stimulates the uptake of 45 Ca into (3-cell-rich pancreatic islets isolated from ob / ob -mice. The distribution of the incorporated radioactivity was analysed by labelling the organelles with 45 Ca in their cellular environment. The radioactive content of the organelles was measured after homogenization and fractionation of the islets under conditions preventing 45 Ca redistribution. The 45 Ca taken up in response to glucose appeared essentially in the secretory granule fraction and in that enriched in mitochondria. Modification of the 45 Ca loading procedure, involving reduction of the oxygen tension and incubation volume, resulted in the disappearance of the glucose effect on the mitochondrial fraction whereas part of the stimulatory effect on the secretory granules persisted. Buffering of calcium by the secretory granules and mitochondria may be important for regulating the cytoplasmic Ca 2+ involved in stimulus-secretion coupling.