Rate-dependent electrophysiological effects of OPC-8212: comparison to sotalol

The rate-dependent effects of OPC-8212 (6 microM), a new positive inotropic drug which lengthens cardiac action potential duration were studied in dog cardiac Purkinje fibers and compared to the effects of sotalol (30 microM), a class III antiarrhythmic using conventional microelectrode technique. Both OPC-8212 and sotalol lengthened action potential duration in a frequency-dependent manner. Both had a greater effect at slower pacing frequencies than at fast. The maximum rising velocity of the action potential upstroke was not affected by either compound at any of the pacing cycle lengths applied (300-2000 ms). The effects of OPC-8212 and sotalol on action potential duration and maximum rising velocity were also compared following abrupt changes in pacing cycle length (i.e. coupling intervals ranging between approximately 250-3000 ms). The effects of both OPC-8212 and sotalol following abrupt changes in pacing cycle length were similar to one another. Neither OPC-8212 nor sotalol altered the time constants for restitution of action potential duration or the kinetics for recovery of the maximum rising velocity of the action potential upstroke. These results indicate that the rate-dependent electrophysiological effects of OPC-8212 closely mimic those of sotalol and suggest that OPC-8212 may be an effective class III antiarrhythmic in addition to being a positive inotropic compound.