Rate- and voltage-dependent effects of m-nisoldipine on action potential of partially depolarized guinea pig papillary muscle

The rate- and voltage-dependent effects of m-Nis were studied using standard microelectrode technique and real-time microcomputer analyzing system. The onset rate for rate-dependent inhibition (RDI) on action potentials of partially depolarized papillary muscle of guinea pig was accelerated as the concentration of m-Nis was increased from 0.5 to 2 mumol.L-1 or the driving frequency decreased from 0.8 to 0.2 Hz. The steady-state values of Vmax and APA were markedly decreased by elevating the concentration of m-Nis or increasing the driving frequency. The recovery time constants of Vmax, APA, and latency period from RDI were all increased by m-Nis (1 mumol.L-1). The inhibitory effects of m-Nis on Vmax and APA were more pronounced as the resting membrane potential was decreased by elevating K+ concentration in the perfusate.