[Lidocaine action on the ion currents of normal and depolarized myocardial fibers in membrane potential fixation].

The effect of lidocaine on the transmembrane ion currents of normal and partially depolarized atrial trabecula was studied in the frog by fixation of membrane potential with duoble sucrose bridge. Lidocaine in a concentration below 12 X 10(-4) g/ml produced no effect on the slow input current. Lidocaine decreased the potassium conduction at the membrane potential values below--45 mW, and increased at--30 mW. Kinetic parameters of the rapid input sodium current and its amplitude significantly changed under the action of lidocaine in normal cardiac tissue, and its effect increased in the depolarized tissue. It is suggested that depolarization is a factor increasing sensitivity to lidocaine of rapid sodium canals, while the capacity of lidocaine to inhibit effectively the rapid sodium current in the partially depolarized myocardium determine its antiarrhythmic activity.