CHLORIDE-HYDROXYL EXCHANGE IN THE GUINEA-PIG VENTRICULAR MYOCYTE - NOROLE FOR BICARBONATE

Reduction of extracellular pH (pH(2)) leads to a fall of intracellular pH (pH(i)) in the guinea-pig ventricular myocyte. In nominally CO2/HC O3-- free conditions, this has been attributed to stimulation of OH- i on efflux on a novel Cl--OH- exchange carrier in the sarcolemma. In th e present work, we have tested for the possible participation of bicar bonate ions. Residual bicarbonate levels may occur through hydration o f CO2 arising either from cellular metabolism or from the atmosphere. The pH(i) was measured by using the intracellular pH-fluorophore, carb oxy SNARF-1 (AM-loaded). Possible sources of CO2 were eliminated by ad ding the aerobic inhibitors, cyanide or rotenone, and by equilibrating the superfusates flowing over the myocyte with a CO2-free, 100% N-2 a tmosphere. The fall of pH(i) upon reducing pH, (to 6.4) persisted afte r complete CO2-removal. This indicates that, in nominally CO2-free con ditions, residual HCO3- transport on a Cl--HCO3- exchanger cannot acco unt for the pH(o)-dependence of pH(i), and supports the hypothesis for a Cl--OH- exchanger (or, alternatively, an H+-Cl- co-influx mechanism ). (C) 1997 Academic Press Limited.