Caffeine releases a glucose-primed endoplasmic reticulum Ca2+ pool in the insulin secreting cell line INS-1

Caffeine mobilized an intracellular Ca2+ pool in intact fura-2-loaded INS-1 cells in suspension exposed to high (16 mM) [glucose], while a minor effec t was observed with low (2 mM) [glucose]. Cells were kept in a medium conta ining diaxozide or no Ca2+ to prevent the influx of extracellular Ca2+. The caffeine-sensitive intracellular Ca2+ pool was within the endoplasmic reti culum since it was depleted by the inhibitor of the reticular Ca2+ pumps th apsigargin and the InsP(3)-dependent agonist carbachol, No effect of caffei ne was observed in the parent glucose-insensitive RINmF5 cells. In microsom es from INS-1 but not RINmF5 cells, the type 2 ryanodine receptor was prese nt as revealed by Western blotting, It was concluded that the endoplasmic r eticulum of INS-1 cells possesses caffeine-sensitive type 2 ryanodine recep tors Ca2+ channels. (C) 1999 Federation of European Biochemical Societies.