Electrophysiological effects of m-nisoldipine and nisoldipine on pacemaker cells in sinoatrial node of rabbits

The effects of m-nisoldipine (m-Nis) and nisoldipine (Nis) on the electrical activity of pacemaker cells in sinoatrial node (SAN) of rabbit were studied using intracellular microelectrodes. RESULTS: APA and Vmax in SAN pacemaker cells were markedly reduced by m-Nis and Nis. The inhibitory effects of Nis on APA and Vmax were greater than those of the m-Nis. Elevation of Ca2+ concentration in the perfusate partially antagonized the inhibitory actions of m-Nis and Nis. VDD of SAN pacemaker cells were reduced by m-Nis. The change of RPF was not consistent with that of VDD. CSRT was prolonged by m-Nis and Nis in a dose-dependent manner. The inhibitory effects of Nis on SAN pacemaker cells were greater than that of the m-Nis. Both MDP and APD50 were not affected by m-Nis and Nis.