Na+/H+ exchange and the regulation of intracellular pH in polymorphonuclear leukocytes

1. Regulation of the cytoplasmic pH(pHi) was studied in quiescent and activated human neutrophils. Acid-loaded unstimulated cells regulate pHi by activating an electroneutral Na+/H+ exchange. 2. When activated, neutrophils undergo a biphasic change in pHi: an acidification followed by an alkalinization. The latter is due to stimulation of the Na+/H+ antiport. 3. The acidification, which is magnified in Na+-free or amiloride-containing media, is associated with net H+ efflux from the cells. 4. A good correlation exists between cytoplasmic acidification and superoxide generation: inhibition of the latter by adenosine, deoxyglucose or pertussis toxin also inhibits the pHi changes. 5. Moreover, acidification is absent in chronic granulomatous disease patients, which cannot generate superoxide. 6. Regulation of pHi is essential for neutrophil function. The oxygen dependent bactericidal activity is inhibited upon cytoplasmic acidification. This can result from impairment of Na+/H+ exchange, or from influx of exogenous acid equivalents. 7. The latter mechanism may account for the inability of neutrophils to resolve bacterial infections in abscesses, which are generally made acidic by accumulation of organic acids that are by-products of bacterial anaerobic metabolism.