Spontaneous calcium oscillations in clonal endocrine pancreatic glucagon-secreting cells.

Measurements of the cytosolic calcium concentration in single cells of the clonal endocrine pancreatic glucagon-secreting cell line INR1 G9 revealed the existence of spontaneous calcium oscillations in 20-70% of these cells. Inhibition of these spontaneous oscillations by thapsigargin as well as the phospholipase C inhibitor U 73122 demonstrated involvement of calcium release from intracellular stores, probably mediated by a high basal activity of phospholipase C. Removal of extracellular calcium but not the L-type calcium channel antagonists verapamil or nifedipine terminated the spontaneous oscillations, suggesting that calcium influx by a pathway distinct from L-type channels contributed to the oscillations. Similar spontaneous calcium oscillations could be the pacemaker of pulsatile glucagon release in endocrine pancreatic A-cells.