Intracellular alkalinization caused by chloride removal in the smooth muscle of guinea-pig vena cava

Intracellular pH (pHi) of smooth muscle of guinea-pig vena cava was measured with a pH-sensitive dye, 4',5'-dimethyl-5-(and -6-)carboxyfluorescein. Sustained intracellular alkalinization (pHi 7.46) was produced when Cl- was replaced with gluconate in the presence of HCO3-, but not produced in the absence of HCO3-. Alkalinization caused by Cl- removal was nearly completely blocked by 200 microM DIDS, a Cl- transport inhibitor. In the solution containing normal Cl- concentration, pHi (7.15) was not affected by DIDS, and pHi was also nearly the same in the presence and absence of HCO3-. When full alkalinization was developed in Cl(-)-deficient solution, HCO3- removal produced only a weak recovery. A carbonic anhydrase inhibitor, acetazolamide (100 microM) had no clear effect on pHi in both normal and Cl(-)-deficient solutions. Intracellular acidification caused by Na+ removal was much less when NaCl was replaced with sucrose than with N-methyl-D-glucamine chloride. It is concluded that when Cl- is removed, pHi can be strongly altered by a Cl(-)-HCO3- exchange mechanism in the guinea-pig vena cava. A contribution of this mechanism to pHi is, however, probably rather minor under physiological conditions.