Exposure of isolated pancreatic islets (mouse or rat) to low temperature (2° C) evoked a threefold increase in insulin release irrespective of the glucose concentration in the incubation medium. Cold-induced release was transient and rewarming to 37° C restored the sensitivity of B-cells to glucose stimulation. In islets cooled to 2° C, exocytotic profiles could easily be detected both by thin-section and freeze-fracture electron microscopy. As revealed by the freeze-fracture technique, the number of exocytotic profiles per membrane area was increased three-to fourfold as compared to islet cells incubated at 20° C. This was paralleled by intracellular fusion of secretory vesicles. Cold-induced insulin release was not affected by theophylline, cytochalasin B, omission of extracellular Ca++ or D600. Replacement of extracellular Na+ with choline or sucrose suppressed the increase in insulin release and in frequency of exocytotic profiles recorded after exposure to 2° C. It is suggested that a redistribution of Ca++ from intracellular stores, possibly mediated by an increase in intracellular Na+, triggers exocytosis of insulin granules upon exposure to cold.
- Isolated pancreatic islets
ASJC Scopus subject areas
- Pathology and Forensic Medicine
- Cell Biology