Effects of m-nisoldipine on delayed afterdepolarization of canine Purkinje fibers.

Effects of m-nisoldipine (m-Nis) on delayed after depolarization (DAD) and triggered activity (TA) were studied using standard microelectrode technique. The development of DAD and TA were markedly inhibited by pre-treatment with m-Nis (1-4 mumol.L-1) as well as m-Nis treatment after DAD and TA had been elicited. The amplitude of DAD was reduced from 15.3 +/- 2.7 to 2.3 +/- 2.0 mV, and the duration from 980 +/- 45 to 130 +/- 27 ms. The occurrence of TA was also reduced or prevented by m-Nis. These effects of m-Nis might be attributed to its blocking effects on voltage-dependent calcium channel and the resultant alleviation of intracellular calcium overload.