Cytoplasmic pH regulation in activated human neutrophils: effects of adenosine and pertussis toxin on Na+/H+ exchange and metabolic acidification

Abstract

When stimulated, neutrophils undergo a complex change in cytoplasmic pH (pHi): an incipient acidification, followed by an alkalinization which is due to activation of Na+/H+ exchange. When the latter is inhibited by amiloride or by removal of extracellular Na+, the actual magnitude of the initial acidification can be fully appreciated. The acidification is thought to be of metabolic origin, but the precise origin of the H+ (equivalents) remains undefined. We used adenosine, a modulator of neutrophil responsiveness, to identify the source of metabolic acid in cells stimulated by either formylmethionylleucylphenylalanine (fMet-Leu-Phe) or 12-O-tetradecanoylphorbol 13-acetate (TPA). Pretreatment of the cells with adenosine inhibited the fMet-Leu-Phe-induced respiratory burst, but secretion of specific and azurophilic granules, as well as aggregation were unaffected. In fMet-Leu-Phe-treated cells, adenosine reduced the acidification recorded in Na+-free media, but had no effect on the activation of the Na+/H+ antiport. Adenosine had little or no effect on the TPA-induced responses, including the pHi changes. The respiratory burst, as well as the cytoplasmic acidification were also inhibited in parallel by pretreating the cells with 'islet-activating protein' from Bordetella pertussis. It was concluded that activation of the NADPH-oxidase and/or the associated stimulation of the hexose monophosphate shunt play a major role in the metabolic acidification of stimulated neutrophils.