The effect of extracellular low pH on the plateau current in isolated, single rat ventricular cells--a voltage clamp study.

When the electrical properties of single, isolated, rat ventricular cells at low pH were examined, the amplitude of the action potential and its duration were found to decrease at low pH (less than 5.5). In voltage clamp experiments, the low pH depressed Ia and slowed the inactivation process, yet the outward currents reflecting the plateau range of the action potential were not affected. The I-V curve of Is shifted to less negative potentials at low pH. Similar results were obtained in ISr and IBa at low pH. The alteration of the action potential of single ventricular cells at low pH is attributed to the suppression of Is. The mechanism of this reduction of Is might be due to the presence of a surface potential capable of affecting gating and permeation mechanisms of Is channel or to the protonation of some acidic group that must be ionized for the Is channel to function normally.