Calcium and pancreatic beta-cell function. 2. Mobilisation of glucose-sensitive 45Ca from perifused islets rich in...

beta-Cell-rich pancreatic islets were microdissected from ob/ob-mice and loaded with 45Ca in the presence of 3 or 20 mM glucose. Subsequent measurements of the effluxes of radioactivity in a perifusion apparatus revealed that the slowly exchangeable 45Ca taken up in response to glucose was also preferentially mobilised by this compound. Glucose stimulation of 45Ca efflux was abolished after omission of calcium from the perifusion medium but persisted when insulin release was inhibited by prolonged starvation, addition of L-epinephrine or lowering of temperature. The presence of a stimulated efflux of radioactivity even under conditions of inhibited insulin release indicates that sources other than beta-granules ejected by exocytosis contribute to the additional 45Ca released after raising the glucose concentration of the perifusion medium. It is suggested that the beta-cell depolarisation as such may account for part of the 45Ca mobilised by glucose.