The effects of intracellular protons on the electrical activity of single ventricular cells

Acidic or alkaline solutions were injected into single guinea-pig ventricular cells and the effects of cytoplasmic proton concentrations ([H]i) on their electrical activity were examined. Injections of low pH (3.7-4.7) solutions shortened the action potential and depressed the plateau by decreasing isi and increasing the outward current at the plateau potentials. Injections of high pH (9.3-9.7) solutions had the opposite effects on the action potential and the membrane currents. A decremental oscillatory current, similar to the strophanthidin-induced transient inward current, was generated upon injecting large amount of low pH solutions. Injections of high pH solution abolished this current. Alterations in [Ca]i also mimiced the changes of the action potential caused by H+-injections. Comparison of the effects of high pH and EGTA injections, however, disclosed marked different actions of these agents on the inactivation process of isi. Therefore, it may be concluded that a combination of a direct effect of the alterations in [H]i and an effect due to changes in [Ca]i secondary to proton injections, causes the above electrical changes of single ventricular cells.