Catecholamine secretion from bovine adrenal chromaffin cells: The role of the Na+/Ca2+ exchanger and the intracellular Ca2+ pool

The role of the Na+/Ca2+ exchanger and intracellular nonmitochondrial Ca2+ pool in the regulation of cytosolic free calcium concentration ([Ca2+](i)) during catecholamine secretion was investigated, Catecholamine secretion and [Ca2+](i) were simultaneously monitored in a single chromaffin cell. After high-K+ stimulation, control cells and cells in which the Na+/Ca2+ exchange activity was inhibited showed similar rates of [Ca2+](i) elevation. However, the recovery of [Ca2+](i) to resting levels was slower in the inhibited cells. Inhibition of the exchanger increased the total catecholamine secretion by prolonging the secretion. Inhibition of the Ca2+ pump of the intracellular Ca2+ pool with thapsigargin caused a significant delay in the recovery of [Ca2+](i) and greatly enhanced the secretory events. These data suggest that both the Na+/Ca2+ exchanger and the thapsigargin-sensitive Ca2+ pool are important in the regulation of [Ca2+](i) and, by modulating the time course of secretion, are important in determining the extent of secretion.