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Catecholamine Secretion from Bovine Adrenal Chromaffin Cells: The Role of the Na+/Ca2+ Exchanger and the Intracellular Ca2+ Pool

Abstract: 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.