Sarcolemmal mechanisms for pH i 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 % CO 2 /HCO 3 − 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 CO 2 ‐dependent buffering. The slow phase was inhibited completely by Cl − removal but not by Na + o removal or K + o elevation. 4 At a test pH i of 7.30 in CO 2 /HCO 3 − buffer, the slow phase was inhibited 70 % by DIDS. The mean DIDS‐inhibitable acid influx was equivalent in magnitude to the HCO 3 − ‐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 − ‐HCO 3 − anion exchanger (AE) to produce HCO 3 − 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 (AE 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.