Dual Effects of Veratridine on Glucagon and Insulin Secretion: Dependence upon Extracellular and Intracellular Calcium

The stimulatory effect of the sodium ionophore, veratridine (10, 25, and 50 μM), on glucagon and insulin secretion was investigated using monolayer cultures of newborn rat pancreas. The results suggest that intracellular accumulation of sodium modulates hormone secretion from both alpha- and beta-cells. The action of veratridine is dependent, at least in part, on the extracellular calcium, as its effect was attenuated or lost when extracellular calcium was deleted. Its action was also dependent on intracellular calcium since preincubation of cells in low, normal, or high calcium to diminish, maintain, or increase intracellular calcium, followed by incubation with veratridine in the absence of calcium, altered the secretory responses of both glucagon and insulin. Ouabain (0.5 mM) stimulated glucagon and insulin secretion, although its effect was less than that of veratridine (50 μM). These results suggest that a common releasing mechanism, dependent on extra- and intracellular calcium, is involved in both endocrine cells.