SUPPRESSION OF CA2-PRODUCING ALPHA(2)-CELLS BY INSULIN GLUCOSE AND AMINO-ACIDS( OSCILLATIONS IN GLUCAGON)

The cytoplasmic Ca2+ concentration ([Ca2+](i)) was continuously monito red in single glucagon-producing alpha(2)-cells isolated from the mous e pancreas and later identified by immunostaining. Up to 60% of the al pha(2)-cells exhibited spontaneous [Ca2+], oscillations (frequency 0.1 -0.3/min) in a medium containing 3 mM glucose. In originating from a b asal level of 60-100 nM, reaching peak values of 300-400 nM and prompt ly disappearing after blocking voltage-dependent Ca2+ channels with me thoxyverapamil, the oscillations resembled those in insulin-releasing beta-cells stimulated by glucose. The oscillatory activity was suppres sed when combining elevation of glucose to 20 mM with the addition of 2-2000 ng/ml insulin. Whereas 10 mM of L-arginine or L-glycine transfo rmed the oscillations into sustained elevation of [Ca2+], there was no response to 1 mM tolbutamide or 0.1-1 mM gamma-aminobutyric acid. The observations that alpha(2)-cells differ from islet cells secreting in sulin and somatostatin in responding to adrenaline with mobilisation o f intracellular calcium can be used for their rapid identification. It is suggested that the oscillations reflect periodic entry of Ca2+ due to variations of the membrane potential.