AJP - Lung Cellular and Molecular Physiology, Vol 266, Issue 6 681-L688, Copyright © 1994 by American Physiological Society
pHi regulation in alveolar macrophages: relative roles of Na(+)-H+ antiport and H(+)-ATPase
A. Bidani, S. E. Brown and T. A. Heming
Department of Internal Medicine, University of Texas Medical Branch, Galveston 77550.
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)
