Effects of prenylamine on transmembrane action potentials as related to the change in external potassium concentrations in guinea pig papillary muscle.

We studied the effects of 4.8 muM prenylamine on transmembrane potentials in isolated guinea pig papillary muscles using a conventional microelectrode technique and compared them with those of 36.9 microM lidocaine. Prenylamine reduced Vmax at 1 Hz increasingly as the external potassium, [K]o, was increased from 2.7 to 10 mM. The reduction was also increased as the driving rate was increased from 0.25 to 5 Hz. The rate-dependent depression was less in 2.7 and 8.1 mM with 7.2 mM [Ca]o and more in 5.4 and 8.1 mM [K]o with 1.8 mM [Ca]o. Prenylamine produced a marked delay in the recovery of Vmax in premature responses inserted between constant driving stimuli at 0.25 Hz. The delay was also less in the former two, and more in the latter two media. Thus the effects of prenylamine on Vmax were more rate dependent and less [K]o-dependent than those of 36.9 microM lidocaine. At the diastolic interval of 100 ms, prenylamine depressed the overshoot, action potential duration at 0 mV level (APDo) and Vmax in premature responses more markedly than did 36.9 microM lidocaine, the differences of the effects being more significant for the first two. The results are interpreted as representing the calcium-antagonistic property of prenylamine of which lidocaine appears to be devoid.