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

Effects of extracellular pH on the sodium current (INa) of single rat ventricular cells were examined under conditions of voltage clamp and internal perfusion. In this way, pHi was controlled while pHo 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+ depressed INa and slowed inactivation. The current-voltage curves for INa were shifted to positive and negative potentials at low and high pHo, respectively. Similar potential shifts were observed in both the conductance voltage curve and the steady-state inactivation voltage curve (h infinity). Conduction was also depressed at low pHo. 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.