Effects of Calcium, Lanthanum, and Bicarbonate Ion on Epinephrine Modification of Insulin Release In Vitro

The role of calcium flux in mediating epinephrine modification of insulin release was investigated by using lanthanum, an inhibitor of calcium flux, in the in vitro perifusion system. Lanthanum inhibits insulin secretion stimulated by glucose and by acetylcholine to basal levels. Epinephrine and lanthanum have additive effects in inhibiting insulin secretion to glucose stimulation. The effect of epinephrine prestimulation on insulin secretion to subsequent glucose challenge varies markedly, depending on the presence or absence of bicarbonate ion: epinephrine priming is reversed inthe absence of bicarbonate, an effect possibly related to reduced calcium uptake. In the presence of bicarbonate, lanthanum blocks the priming effect of epinephrine on insulin secretion. The data further support the postulated role of calcium in adrenergic effects on beta cell function.