Sarcolemmal mechanisms for pHi recovery from alkalosis in the guinea-pig ventricular myocyte.
1. The mechanism of pHi recovery from an intracellular alkali load (induced by acetate prepulse or by reduction/removal of ambient PCO2) was investigated using intracellular SNARF fluorescence in the guinea-pig ventricular myocyte. 2. In Hepes buffer (pHo 7.40), pHi 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 (pHo 7.40), pHi 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 pHi of 7.30 in CO2/HCO3- buffer, the slow 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 pHi 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 (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.
Leem
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University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, UK.
Vaughan-Jones
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D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000085:Acetates / Q000494:pharmacology; D000471:Alkalosis; D000818:Animals; D001578:Benzopyrans; D002478:Cells, Cultured; D002712:Chlorides / Q000494:pharmacology; D005456:Fluorescent Dyes; D006168:Guinea Pigs; D006531:HEPES; D006321:Heart / Q000502:physiology*; D006352:Heart Ventricles; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology
D000085:Acetates; D001578:Benzopyrans; D002712:Chlorides; D005456:Fluorescent Dyes; C063917:SNARF dye; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; C036010:4,4'-dibenzamido-2,2'-stilbenedisulfonic acid; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D006531:HEPES