CYTOSOLIC PH REGULATION IN MOUSE MACROPHAGES - PROTON EXTRUSION BY PLASMA-MEMBRANE-LOCALIZED H+-ATPASE

Recent evidence indicates that H+ extrusion in macrophages is in part accomplished by a H+ -ATPase of vacuolar type. The presence and plasma-membrane localization of such a mechanism in adherent resident macrophages was verified by inhibition of H+ extrusion, monitored by changes in both cytosolic pH (pH(i)) and extracellular pH, with low concentrations of the H+ -ATPase inhibitors N-ethylmaleimide and 7-chloro-4-nitrobenz-2-oxa-1,3-diazole. The H+ -ATPase was operative at physiological pH(i) levels, thus contributing to maintenance of steady-state pH(i). It was further shown to be sensitive to the plasma-membrane potential, with hyperpolarization being strongly inhibitory. In addition, H+ extrusion mediated by the H+ -ATPase and the generation and release of lactic acid caused acidification of the pericellular space and could enable secreted lysosomal hydrolases to act extracellularly.