Effects of the local anesthetics brufacain and lidocaine on transmembrane action potentials, refractory period, and reactivation of the sodium system in guinea pig heart muscle.

Lidocaine (3-10(-5) and 10(-4) M) and equimolar concentrations of brufacain dose-dependently reduced the depolarization velocity (dV/dtmax) and the force of contraction of guinea pig atria and papillary muscles. Repolarization time was increased in atria but reduced in papillary muscles. The maximum effects on action potential parameters were identical but developed with brufacain more slowly than with lidocaine. In papillary muscles lidocaine (3-10(-5) M) prolonged the functional refractory period. No such effect but even a shortening was observed with brufacain. As brufacain reduced the duration of the action potential (AP) more than the functional refractory period, the "relative refractory period" (in percent of AP duration) was slightly prolonged. The half-time of the recovery of the Na+ system was increased three to five times the control value after lidocaine but only doubled after brufacain.