Phorbol ester-stimulated human neutrophil membrane depolarization is dependent on Ca2+-regulated Cl- efflux

JEROME B. MYERS, HORACIO F. CANTIELLO,JOHN H. SCHWARTZ, AND ALFRED I. TAUBER

AMERICAN JOURNAL OF PHYSIOLOGY-CELL PHYSIOLOGY

Año: 1990 p. 531 - 540

0363-6143

The ionic basis of phorbol12-myristate 13- acetate (PMA)-stimulated membrane depolarization in the human neutrophil has not previously been established. Alterations in cation permeability are probably not directly responsible for the depolarization response, since the rate of Rb’ influx or efflux is unchanged upon PMA stimulation, and although Na+ fluxes are increased, depolarization is not changed by either the addition of ouabain or reduction of extracellular Na+ from 140 to 0 meq. Furthermore, the enhanced Na+ influx in stimulated cells is blocked by amiloride at low3 M, but not by 10W5 M, suggesting Na+ influx proceeds through the electroneutral Na’-H’ antiporter and is therefore not responsible for depolarization. Upon stimulation, Cl- content of PMA-stimulated neutrophils decreases without change in Na+ or K’ content, as determined by electron probe analysis. In addition, acute reduction in extracellular Cl- enhances the rate and extent of depolarization induced by PMA. This change in intracellular Cl- and effect of reduction in extracellular Cl- concentration on depolarization can best be accounted for by an enhanced efflux via an electrogenic mechanism. Thus enhanced conductive Cl- efflux can account for the observed depolarization. That Ca2’ regulates depolarization is evidenced by the dependence of depolarization on external Ca2+ (C&‘). Depolarization is absent in Ca2+-depleted cells [internal Ca2+ (Caz’) Cl5 nM] and is restored with titration of extracellular Ca2+, exhibiting a 50% effective dose (ED& of 100 mM. Thus PMA-initiated depolarization is regulated by Ca2’, either from intra- or extracellular sources, but the Ca2+-dependent activity responsible for control of Cl- efflux is as yet uncharacterized.