Intracellular pH in quiescent and stimulated ventricular myocardium. Effect of extracellular chloride concentration

In ventricular trabeculae from guinea pig and cat heart superfused with a modified Tyrode's solution (pHo = 7.4) containing either 137 mM or 103 mM Clo-, intracellular pH (pHi) was measured with H+-sensitive double-barreled microelectrodes. In quiescent preparations pHi was 7.26 +/- 0.017 when Clo- was 137 mM, and 7.38 +/- 0.02 in 103 mM chloride. In 103 mM Clo- containing saline stimulation of the preparation produced no acidification but in 137 mM Clo- acidification occurred. The acidification was completely reversible when chloride was reduced again. When HCO3-/Cl- exchange was blocked by 0.5 mM SITS, pHi was lowered similar to the effect of increasing extracellular chloride concentration. It was concluded that when Clo- is raised, the HCO3-/Cl- exchanger operates as a Cl-/Cl- exchanger.