title: Cytoplasmic pH regulation in phorbol ester-activated human neutrophils.
abstract: Activation of neutrophils by 12-O-tetradecanoylphorbol-13-acetate (TPA) is accompanied by an initial cytoplasmic acidification, followed by an alkalinizing phase due to Na+-H+ countertransport. The source of the acidification, which is fully expressed by activation with TPA in Na+-free or amiloride-containing media, was investigated. The acidification phase was detected also in degranulated and enucleated cytoplasts, ruling out a major contribution by the nucleus or secretory vesicles. Cytoplasmic acidification was found to be associated with an extracellular acidification, suggesting metabolic generation of H+. Two principal metabolic pathways are stimulated in activated neutrophils: the reduction of O2 by NADPH-oxidase and the hexose monophosphate shunt. A good correlation was found between the activity of these pathways and the changes in cytoplasmic pH. Inhibition of superoxide synthesis prevented the TPA-induced cytoplasmic acidification. Moreover, activation of the hexose monophosphate shunt with permeable NADPH-oxidizing agents (in the absence of TPA) also produced a cytoplasmic acidification. Cytoplasmic acidification was also elicited by exogenous diacylglycerol and by other beta-phorbol diesters, which are activators of the kinase, but not by unesterified phorbol or by alpha-phorbol diesters, which are biologically inactive. The results suggest that the cytoplasmic acidification induced by phorbol esters in neutrophils reflects accumulation of H+ liberated during the metabolic burst that follows activation.
mesh_terms: D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D008213:Lymphocyte Activation; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D019255:NADPH Oxidases; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D010427:Pentose Phosphate Pathway; D010703:Phorbol Esters / Q000494:pharmacology; D010704:Phorbols / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013268:Stimulation, Chemical; D013481:Superoxides / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D007473:Ion Channels; D010703:Phorbol Esters; D010704:Phorbols; D013481:Superoxides; D012964:Sodium; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate