Na(+)-HCO3- symport modulates intracellular pH in alveolar epithelial cells.
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.
Lubman
R L
RL
Will Rogers Institute Pulmonary Research Program and Center, Cornell University, New York, New York 10021.
Crandall
E D
ED
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D002352:Carrier Proteins / Q000502:physiology*; D002478:Cells, Cultured; D002712:Chlorides / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D011650:Pulmonary Alveoli / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000494:pharmacology; D027982:Sodium-Bicarbonate Symporters
D001639:Bicarbonates; D002352:Carrier Proteins; D002712:Chlorides; D005452:Fluoresceins; D005456:Fluorescent Dyes; D027982:Sodium-Bicarbonate Symporters; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000584:Amiloride; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid