pH regulatory transport systems in a smooth muscle-like cell line.
The membrane transport systems responsible for pH regulation in BC3H-1 cells were studied using the pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF). In nominally CO2-free Na N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid buffer (NHB) recovery from acidification after an NH4Cl pulse was reversibly inhibited by 1 mM amiloride or by Na-free solutions. On exposure to 5% CO2-HCO3 (external pH constant at 7.4), BC3H-1 cells alkalinized by approximately 0.3-0.4 pH unit. This CO2-induced alkalinization was unaffected by 1 mM amiloride, markedly reduced by 0.5 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), and inhibited by Na-free solutions. On readdition of Na, cells rapidly alkalinized, even in the presence of 1 mM amiloride. Exposure to Cl-free CO2-HCO3 solutions caused a rapid alkalinization of nearly 1 pH unit that was abolished by SITS, largely independent of Na, unaffected by amiloride, and unchanged by membrane depolarization in high external K solutions. CO2-induced alkalinization was slowed by approximately 75% after prolonged exposure of cells to Cl-free NHB, but a distinct recovery from acidification remained in these Cl-depleted cells. This recovery was Na-dependent, SITS-inhibitable, and unaffected by depolarization in high-K solutions. In the presence of CO2, the acidification seen in response to NH4Cl-induced alkalinization was reduced 50% by 0.5 mM SITS. These data suggest that the regulation of pH in BC3H-1 cells is mediated by at least three transport systems: 1) Na-H exchange; 2) Cl-HCO3 exchange; and 3) electroneutral (Na + HCO3)-Cl exchange.(ABSTRACT TRUNCATED AT 250 WORDS)
Putnam
R W
RW
Department of Physiology and Biophysics, Wright State University School of Medicine, Dayton, Ohio 45401.
D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002245:Carbon Dioxide / Q000494:pharmacology; D002460:Cell Line; D002712:Chlorides / Q000494:pharmacology; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009130:Muscle, Smooth / Q000378:metabolism*; D013997:Time Factors
D002712:Chlorides; D000643:Ammonium Chloride; D002245:Carbon Dioxide; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000584:Amiloride