AJP - Cell Physiology, Vol 258, Issue 3 C470-C479, Copyright © 1990 by American Physiological Society
pH regulatory transport systems in a smooth muscle-like cell line
R. W. Putnam
Department of Physiology and Biophysics, Wright State University School of Medicine, Dayton, Ohio 45401.
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)
