AJP - Lung Cellular and Molecular Physiology, Vol 260, Issue 6 555-L561, Copyright © 1991 by American Physiological Society

ARTICLES

Na(+)-HCO3- symport modulates intracellular pH in alveolar epithelial cells

R. L. Lubman and E. D. Crandall
Will Rogers Institute Pulmonary Research Program and Center, Cornell University, New York, New York 10021.

We investigated Na(+)-HCO3- cotransport as a mechanism for regulation of intracellular pH (pHi) in rat alveolar pneumocytes grown in primary culture. pHi was monitored using the fluorescent pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Cells incubated in 6 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) medium at pH 7.4 were subjected to rapid acidification by CO2 pulse. pHi recovered in the presence of Na+ with an initial rate (dpHi/dt) of 0.15 min-1, which was reduced by 67% when Na+ was replaced by choline, unaffected by substitution of gluconate for Cl-, reduced 40% in the presence of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS, 500 microM), and unchanged by amiloride (1 mM). In parallel experiments, cells were incubated at pH 7.4 with 20 mM HCO3- and pHi acutely lowered by NH3 prepulse. dpHi/dt in these experiments was 0.14 min-1 in the presence of Na+ and HCO3-, and reduced 79% under Na(+)-free conditions. These data indicate the presence of a Na(+)-dependent, Cl(-)-independent, DIDS-sensitive and amiloride-insensitive mechanism of recovery from acute intracellular acidification in alveolar pneumocytes, most consistent with Na(+)-HCO3- cotransport (symport) effecting acid extrusion under these experimental conditions. This ion transport mechanism may contribute to regulation of pHi in alveolar pneumocytes, transepithelial transport of acid-base equivalents across the alveolar epithelium, and modulation of pH of alveolar fluid in adult mammalian lungs.

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