NA-INDEPENDENT CL--HCO3- EXCHANGE MEDIATES RECOVERY OF PH(I) FROM ALKALOSIS IN GUINEA-PIG VENTRICULAR MYOCYTES

The pH-sensitive fluorescent indicator, carboxy-seminaphthorhodafluor 1 (SNARF 1) was used to assess the contribution of forward Na-independent Cl--HCO3- exchange (1 external Cl- exchanged for 1 internal HCO3-) to intracellular pH (pH(i)) recovery from alkalosis in adult ventricular myocytes (guinea pig). Intracellular alkalosis was elicited by external application of the weak base, trimethylamine. In the absence of CO2-HCO3- (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered solution) the initial rate of pH(i) recovery from alkalosis (pH(i) approximate to 7.25-7.75) was slow and independent of pH(i), yielding an apparent net HCO3- efflux of 0.36 +/- 0.11 mM/min. In CO2-HCO3--buffered solution, the initial rate of pH(i) recovery and net HCO3- efflux were much faster and markedly increased by raising pH(i). At pH(i) approximate to 7.25, net HCO3- efflux was similar to 2 mM/min and rose to 9 mM/min at pH(i) approximate to 7.6. 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (0.4 mM) decreased net HCO3- efflux by 78.1 +/- 8.9% in CO2-HCO3--buffered solution. Reduction in extracellular Cl- concentration from 135 to 20 mM markedly slowed the rate of pH(i) recovery from alkalosis and reduced net HCO3- efflux. pH(i) recovery from alkalosis was unaffected by removal of external sodium or exposure to 1 mM amiloride. These results indicate that forward Na-independent Cl--HCO3- exchange mediates pH(i) recovery from alkalosis in guinea pig ventricular myocytes.