Ca2+ oscillations in pancreatic islet cells secreting glucagon and somatostatin.

Immunohistochemically identified glucagon-releasing alpha 2-cells from mouse pancreatic islets exhibited large amplitude oscillations of the cytoplasmic Ca2+ concentration in 3 mM glucose. Other small islet cells with similar oscillations in the presence of 20 mM glucose were identified as somatostatin-releasing alpha 1-cells. The oscillations in both cell types resembled those induced by glucose in the surrounding larger beta-cells in starting from the basal level and disappearing after addition of the voltage-dependent Ca2+ channel blocker methoxyverapamil. The discovery that the alpha 1- and alpha 2-cells have intrinsic abilities to generate oscillatory Ca2+ signals indicates that pulsatile release of somatostatin and glucagon do not require functional coupling to the beta-cells.