Modulation of intracellular pH by secretagogues and the Na+/H+ antiporter in cultured bovine chromaffin cells

Abstract

The possible physiological role of cytosolic pH changes in adrenal medullary chromaffin cell secretion was examined by investigating the effects of catecholamine secretagogues on cytosolic pH, which was monitored using the intracellular fluorescent indicator 2′,7′-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Anti-fluorescein antibodies were used to reduce background fluorescence from extracellular 2′,7′-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Stimulation with both cholinergic agonists (acetylcholine, nicotine) and a depolarizing agent (high K+) transiently acidified the cytosol of the chromaffin cell. This acidification was antagonized by reducing extracellular Ca2+ concentration and by Ca2+ antagonists (Co2+, verapamil), indicating that it occurred secondarily to Ca2+ influx, possibly as a result of exchange of Ca2+ ions for protons across organelle membranes. Taken together with previously published data [Kuijpers G.A.J. et al. (1989) J. biol. Chem. 264, 698-70