PH(I) REGULATION IN ALVEOLAR MACROPHAGES - RELATIVE ROLES OF NA-H+ ANTIPORT AND H+-ATPASE()

In rabbit alveolar macrophages, recovery of intracellular pH (pH(i)) f rom acid loads to pH(i) values greater than or equal to 6.8 at an extr acellular pH (pH(o)) of 7.4 (nominal absence of CO2-HCO3-) is insensit ive to amiloride, an inhibitor of Na+-H+ exchange, and abolished by ba filomycin A(1), an inhibitor of vacuolar-type H+-ATPase [A. Bidani, S. E. S. Brown, T. A. Heming, R. Gurich, and T. D. Dubose, Jr. Am. J. Ph ysiol. 257 (Cell Physiol. 26): C65-C76, 1989; A. Bidani and S. E. S. B rown. Am. J. Physiol. 259 (Cell Physiol. 28): C586-C598, 1990]. To fur ther evaluate the roles of Na+-H+ exchange and H+-ATPase activity in p H(i) regulation in rabbit alveolar macrophages, we have investigated t he effects of amiloride and bafilomycin over a greater range of pH(i) (6.3-7.0) and pH(o) (5.0-7.4). The results indicate that rabbit alveol ar macrophages possess H+-ATPase and a Na+-H+ antiporter, both of whic h are activated by decrements in pH(i). However, in all cases, H+-ATPa se activity exclusively determined basal pH(i) and was the principal m echanism (> 50%) for pH(i) recovery from intracellular acid loads. The pH(i) set point for activation of Na+-H+ exchange was similar to 6.8 at pH(o) of 7.4 and similar to 6.5 at pH(o) of 6.8. Na+-H+ exchange di d not contribute significantly to pH(i) recovery at acid-loaded pH(i) above these set points. At pH(o) of 7.4 and pH(i) greater than or equa l to 6.8, pH(i) recovery displayed an activation energy of similar to 11,000 kcal/mol and temperature coefficient of similar to 2.1, which a re consistent with an energy-dependent process (i.e., H+ pump). Taken together, these data indicate that the plasmalemmal vacuolar-type H+ p ump is the primary mechanism for regulation of pH(i) in rabbit alveola r macrophages. Na+-H+ exchange plays only a minor role, if any, in pH( i) regulation in the physiological range.