AJP - Lung Cellular and Molecular Physiology, Vol 257, Issue 6 438-L445, Copyright © 1989 by American Physiological Society

ARTICLES

Evidence for active H+ secretion by rat alveolar epithelial cells

R. L. Lubman, S. I. Danto and E. D. Crandall
Will Rogers Institute Pulmonary Research Program, Cornell University Medical College, New York, New York 10021.

A plasma membrane proton-translocating adenosinetriphosphatase (ATPase) has been identified in rat alveolar pneumocytes in primary culture using the pH-sensitive fluorescent probe 2',7'-biscarboxyethyl-5,6-carboxyfluorescein. Intracellular pH (pHi) was acutely lowered by NH3 prepulse in HCO3(-)-free medium buffered with 6 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid, and its recovery was measured thereafter under control conditions, in the presence of amiloride to inhibit Na(+)-H+ antiport, and in the presence of N-ethylmaleimide (NEM), a plasma membrane H(+)-ATPase inhibitor. Initial rate of pHi recovery was reduced by 67% in the presence of amiloride, 52% in the presence of NEM, and 96% in the presence of both. Recovery was decreased but not abolished in Na(+)-free buffer, was essentially abolished when NEM was present in the absence of Na+, and was also abolished by addition of the metabolic inhibitor KCN in glucose- and Na(+)-free medium. These data suggest that alveolar epithelial cells possess a plasma membrane H(+)-ATPase. In Na(+)-containing buffer at pH 7.4, steady-state pHi was 7.50. This value was unaffected by amiloride but decreased to 7.01 in the presence of NEM, suggesting active H(+)-ATPase and inactive Na(+)-H+ antiport at steady-state pHi. We conclude that this plasma membrane proton-translocating ATPase in alveolar pneumocytes may be an important mechanism contributing to regulation of steady-state pHi, recovery from acute intracellular acidification, and modulation of extracellular alveolar fluid pH.

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