Voltage- and use-dependent effects of lidocaine on sodium current in rat single ventricular cells

We compared the blocking effects of the local anesthetics, lidocaine and benzocaine, on the sodium current, using single rat ventricular cells to obtain further information about the voltage dependence and kinetics of local anesthetic interaction with cardiac sodium channels. We used a hybrid voltage clamp system which employed a suction pipette for passing current and internal perfusion, and a microelectrode for membrane potential measurement. Lidocaine (20 microM) and benzocaine (100 microM) produced qualitatively similar effects on sodium current when test pulses were applied infrequently. Both of these agents decreased the peak sodium current without producing a shift of the current-voltage curve. They did, however, shift the inactivation curves of sodium current to hyperpolarized potentials; the V0.5 was shifted by -9.5 mV for lidocaine and by -5 mV for benzocaine. Lidocaine produced a significant use-dependent effect that was proportional to the duration of the voltage step. Benzocaine produced only minimal use-dependent effects. The characteristics of the lidocaine block suggest that this agent binds preferentially to inactivated sodium channels and that dissociation from resting channels is voltage-dependent. The differences in lipid solubility and molecular weight between lidocaine and benzocaine may explain the differences in their use-dependent blocking effects on sodium current.