Effect of extracellular pH on sodium current in isolated, single rat ventricular cells

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Abstract
Effects of extracellular pH on the sodium current (I Na) of single rat ventricular cells were examined under conditions of voltage clamp and internal perfusion. In this way, pH i was controlled while pH o was changed. The combined suction pipette-microelectrode method was used. The suction pipette passed current and perfused the cell's interior; the microelectrode measured membrane potential. Increasing extracellular H+ depressedI Na and slowed inactivation. The current-voltage curves forI Na and Slowed inactivation. The current-voltage curves forI Na were shifted to positive and negative potentials at low and high pH o , respectively. Similar potential shifts were observed in both the conductance voltage curve and the steadystate inactivation voltage curve (h ∞). Conduction was also depressed at low pH o . The shifts were probably due to surface charge effects, while the impaired conduction was probably due to protonation of a site in the Na channel.