Control of cytoplasmic pH by Na+/H+ exchange in rat peritoneal macrophages activated with phorbol ester.

The mechanisms underlying cytoplasmic pH (pHi) regulation in elicited rat peritoneal macrophages were investigated by electronic sizing and fluorescence determinations. Acid-loaded cells rapidly regained normal pHi by means of an amiloride-sensitive Na+/H+ exchange. When stimulated by 12-O-tetradecanoyl phorbol 13-acetate, macrophages displayed a biphasic pHi change: a marginal acidification followed by an alkalinization. The latter results from activation of Na+/H+ exchange, since it is Na+-dependent and prevented by amiloride. When the antiport is inhibited, the full magnitude of the initial acidification can be appreciated. This acidification is independent of the nature of the ionic composition of the medium and probably reflects accumulation of protons generated during the metabolic burst. Under physiological conditions, these protons are rapidly extruded by the Na+/H+ antiport.