pHi regulation in alveolar macrophages: relative roles of Na(+)-H+ antiport and H(+)-ATPase.
In rabbit alveolar macrophages, recovery of intracellular pH (pHi) from acid loads to pHi values > or = 6.8 at an extracellular pH (pHo) of 7.4 (nominal absence of CO2-HCO3-) is insensitive to amiloride, an inhibitor of Na(+)-H+ exchange, and abolished by bafilomycin A1, 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. Physiol. 257 (Cell Physiol. 26): C65-C76, 1989; A. Bidani and S. E. S. Brown. Am. J. Physiol. 259 (Cell Physiol. 28): C586-C598, 1990]. To further evaluate the roles of Na(+)-H+ exchange and H(+)-ATPase activity in pHi regulation in rabbit alveolar macrophages, we have investigated the effects of amiloride and bafilomycin over a greater range of pHi (6.3-7.0) and pHo (5.0-7.4). The results indicate that rabbit alveolar macrophages possess H(+)-ATPase and a Na(+)-H+ antiporter, both of which are activated by decrements in pHi. However, in all cases, H(+)-ATPase activity exclusively determined basal pHi and was the principal mechanism (> 50%) for pHi recovery from intracellular acid loads. The pHi set point for activation of Na(+)-H+ exchange was approximately 6.8 at pHo of 7.4 and approximately 6.5 at pHo of 6.8. Na(+)-H+ exchange did not contribute significantly to pHi recovery at acid-loaded pHi above these set points. At pHo of 7.4 and pHi > or = 6.8, pHi recovery displayed an activation energy of approximately 11,000 kcal/mol and temperature coefficient of approximately 2.1, which are consistent with an energy-dependent process (i.e., H+ pump).(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Internal Medicine, University of Texas Medical Branch, Galveston 77550.
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Bidani
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Brown
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Heming
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism*; D018942:Macrolides; D016676:Macrophages, Alveolar / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D011817:Rabbits; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013696:Temperature; D014617:Vacuoles / Q000201:enzymology
D000900:Anti-Bacterial Agents; D018942:Macrolides; D017923:Sodium-Hydrogen Exchangers; C057620:bafilomycin A; D000584:Amiloride; D006180:Proton-Translocating ATPases