Electrophysiological effects of lidocaine on isolated guinea pig Purkinje fibers: comparison with its effects on papillary muscle.

1. The effects of lidocaine on action potentials of isolated guinea pig Purkinje fibers were examined and compared with those on the papillary muscle, by use of conventional microelectrode techniques. 2. Lidocaine 2.1 x 10(-4) M significantly depressed the resting membrane potential, amplitude, overshoot, maximum upstroke velocity, and duration of action potential of the Purkinje fibers stimulated at cycle length (CL) 1 sec, while the lower concentration (2.1 x 10(-5) M) produced no significant effect. 3. Various parameters of action potentials from the papillary muscle at CL = 1 sec were also depressed by lidocaine 2.1 x 10(-4) M, but the extent of the depression was less marked than in Purkinje fibers. 4. When the Purkinje fibers were stimulated at various CLs (0.3-10 sec), the shortening of action potential duration induced by lidocaine was more evident at slower stimulus rate.