Effect of Intravenous Anesthetics on Inward Rectifier Potassium Current in Rat and Human Ventricular Myocytes

Abstract

Background Inhibition of the inward rectifying potassium current (I(K1)) may cause cardiac dysrhythmias by decreasing resting membrane potential or prolonging action potential. Methods The effects of thiopental, ketamine, and propofol on I(K1) conductance were evaluated in rat ventricular myocytes. The effect of thiopental on I(K1) conductance was also evaluated in human ventricular myocytes. Currents were recorded using the nystatin-perforated whole-cell patch-clamp technique (holding potential, -50 mV; test potentials, -140 to -40 mV). Pipette solution contained 130 mM KCl, 5 mM MgCl2, 5 mM HEPES, and 5 mM EGTA,pH 7.2. Bath solution (32 degrees C) contained 134 mM NaCI, 4 mM KCl, 1 mM MgCl2, 1 mM CaCl2, 0.3 mM CdCl2, 5 mM HEPES, and 5 mM d-glucose,pH 7.4. Drug concentrations examined encompassed the range of clinically relevant unbound plasma concentrations. Currents were normalized for cell capacitance. Conductance was calculated as current density/delta mV from -140 to -100 mV. Analysis of variance was used to test for changes in conductance as a function of drug concentration. Results Thiopental reduced I(K1) conductance in a concentration-dependent manner (P < 0.0001). Thiopental-induced changes in I(K1) conductance in rat ventricular myocytes were fit to an inhibitory E(max) model, with a median inhibitory concentration of 10.5 microM. The effect of thiopental on I(K1) conductance in human ventricular cells was comparable to that observed in rat ventricular myocytes. Neither ketamine nor propofol altered I(K1) conductance. Conclusions Thiopental reduces I(K1) conductance in a concentration-dependent manner at clinically relevant concentrations in both rat and human ventricular myocytes.