Sarcolemmal mechanisms for pHi recovery from alkalosis in the guinea-pig ventricular myocyte

1. The mechanism of pH(i) recovery from an intracellular alkali load (induced by acetate prepulse or by reduction/removal of ambient P-CO2) was investigated using intracellular SNARF fluorescence in the guinea-pig ventricular myocyte. 2. In Hepes buffer (pH(o) 7.40), pH(i) recovery was inhibited by removal of extracellular Cl-, but not by removal of Na-o(+) or elevation of K-o(+). Recovery was unaffected by the stilbene drug DIDS (4,4-diisothiocyanatostilbene-disulphonic acid), but was slowed dose dependently by the stilbene drug DBDS (dibenzamidostilbene-disulphonic acid). 3. In 5% CO2/HCO3- buffer (pH(o) 7.40), pH(i) recovery was faster than in Hepes buffer. It consisted of an initial rapid recovery phase followed by a slow phase, Much of the rapid phase has been attributed to CO2-dependent buffering. The slow phase was inhibited completely by Cl-o(-) removal but not by Na-o(+) removal or K-o(+) elevation. 4. At a test pH(i) of 7.30 in CO2/HCO3- buffer, the slaw phase was inhibited 70% by DIDS. The mean DIDS-inhibitable acid influx was equivalent in magnitude to the HCO3--stimulated acid influx. Similarly, the DIDS- insensitive influx was equivalent to that estimated in Hepes buffer. 5. We conclude that two independent sarcolemmal acid-loading carriers are stimulated by a rise of pH(i) and account for the slow phase of recovery from an alkali load. The results are consistent with activation of a DIDS-sensitive Cl--HCO3- anion exchanger (AE) to produce HCO3- efflux, and a DIDS-insensitive Cl--OH- exchanger (CHE) to produce OH- efflux. H+-Cl- co-influx as the alternative configuration for CHE is not, however, excluded. 6. The dual acid-loading system (BE plus CHE), previously shown to be activated by a fall of extracellular pH, is thus activated by a rise of intracellular pH. Activity of the dual-loading system is therefore controlled by pH on both sides of the cardiac sarcolemma.