Effect of Gd3+ on bradykinin-induced catecholamine secretion from bovine adrenal chromaffin cells

1 The effects of Gd3+ on bradykinin- (BK-) induced catecholamine secretion, Ca-45(2+) efflux and cytosolic [Ca2+] were studied using bovine adrenal chromaffin cells. 2 BK increased secretion in a Ca2+-dependent manner. From 1-100 mu M, Gd3+ progressively inhibited secretion induced by 30 nM BK to near-basal levels, however from 0.3-3 mM Gd3+ dramatically enhanced BK-induced secretion to above control levels. Gd3+ also increased basal catecholamine secretion by 2-3 fold at 1 mM. These effects were mimicked by Eu3+ and La3+. 3 Gd3+ enhanced secretion induced by other agonists that mobilize intracellular Ca2+ stores, but simply blocked the response to K+. 4 Gd3+ still enhanced basal and BK-induced secretion in Ca2+-free solution or in the presence of 30 mu M SKF96365, however both effects of Gd3+ were abolished after depleting intracellular Ca2+ stores. 5 Gd3+ (1 mM) reduced the rate of basal Ca-45(2+) efflux by 57%. In Ca2+-free buffer, BK transiently increased cytosolic [Ca2+] measured with Fura-2. The [Ca2+] response to BK was substantially prolonged in the presence of Gd3+ (1 mM). 6 The results suggest that Gd3+ greatly enhances the efficacy of Ca2+ released from intracellular stores in evoking catecholamine secretion, by inhibiting Ca2+ extrusion from the cytosol. This suggests that intracellular Ca2+ stores are fully competent to support secretion in chromaffin cells to levels comparable to those evoked by extracellular Ca2+ entry. Drugs that modify Ca2+ extrusion from the cell, such as lanthanide ions, will be useful in investigating the mechanisms by which intracellular Ca2+-store mobilization couples to Ca2+-dependent exocytosis.