Effects of aprindine on conduction velocity and Vmax in guinea-pig papillary muscles

One of the effects of antiarrhythmic drugs is the reduction of conduction velocity. Cable theory predicts that there is a nonlinear relationship between conduction velocity and upstroke velocity (Vmax) of action potential. By using conventional microelectrode techniques, aprindine-induced reduction of Vmax of action potential and conduction velocity in guinea-pig papillary muscles were measured. Aprindine-produced, use-dependent, and concentration-dependent changes in conduction velocity and the decline of square of conduction velocity was well fit by a single exponential. Time constants for square of conduction velocity were comparable to simultaneously measured time constants for effects of Vmax. At a concentration of 1 to 10 microM aprindine, onset changes between Vmax and conduction velocity had a log-linear relationship in a predicted fashion. Whereas, in the recovery process from aprindine-induced depression, slow recovery time course of conduction velocity was observed. In conclusion, in the presence of aprindine, only onset block of conduction velocity can be analyzed quantitatively in the relationship to observation on Vmax in vitro. These results suggested that in the presence of aprindine, the recovery of internal conductance may be slower than that of Vmax.
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