PHORBOL 12-MYRISTATE 13-ACETATE ACTIVATES AN ELECTROGENIC H+-CONDUCTING PATHWAY IN THE MEMBRANE OF NEUTROPHILS

The mode of activation of an H+-conducting pathway present in the membrane of neutrophils was investigated. (1) Resting neutrophils released protons through an electrogenic Cd2+-inhibitable (K0.5 almost-equal-to 20-mu-M) route when a pH gradient and appropriate charge compensation was provided. (2) The rate of H+ efflux was stimulated over 2.5-fold by 4-beta-phorbol 12-myristate 13-acetate (PMA; K0.5 almost-equal-to 0.7 nM) or by 4-beta-phorbol 12,13-dibutyrate (K0.5 almost-equal-to 20 nM) even when the NADPH oxidase was blocked by p-chloromercuribenzoate. (3) Staurosporine inhibited the effect of PMA. (4) The H+ egress was not enhanced by 4-alpha-phorbol 12,13-didecanoate. (5) Low concentrations of Cd2+ (< 40-mu-M) inhibited the H+ flux without influencing the oxidase. The results raise the possibility that protein kinase C could be involved in the activation of an electrogenic H+-conducting pathway in the membrane of neutrophils. The activation of this route by phorbol esters seems to be independent of the stimulation of NADPH oxidase.