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, Catecholami ne secretion and [Ca2+](i) were simultaneously monitored in a single c hromaffin cell. After high-K+ stimulation, control cells and cells in which the Na+/Ca2+ exchange activity was inhibited showed similar rate s of [Ca2+](i) elevation. However, the recovery of [Ca2+](i) to restin g levels was slower in the inhibited cells. Inhibition of the exchange r increased the total catecholamine secretion by prolonging the secret ion. Inhibition of the Ca2+ pump of the intracellular Ca2+ pool with t hapsigargin caused a significant delay in the recovery of [Ca2+](i) an d greatly enhanced the secretory events. These data suggest that both the Na+/Ca2+ exchanger and the thapsigargin-sensitive Ca2+ pool are im portant in the regulation of [Ca2+](i) and, by modulating the time cou rse of secretion, are important in determining the extent of secretion .