Actions of Mibefradil, Efonidipine and Nifedipine Block of Recombinant T- and L-type Ca Channels with Distinct Inhibitory Mechanisms

We compared detailed efficacy of efonidipine and nifedipine, dihydropyridine analogues, and mibefradil using recombinant T- and L-type Ca2+ channels expressed separately in mammalian cells. All these Ca2+ channel antagonists blocked T-type Ca2+ channel currents (I(Ca(T))) with distinct blocking manners: I(Ca(T)) was blocked mainly by a tonic manner by nifedipine, by a use-dependent manner by mibefradil, and by a combination of both manners by efonidipine. IC50s of these Ca2+ channel antagonists to I(Ca(T)) and L-type Ca2+ channel current (I(Ca(L))) were 1.2 micromol/l and 0.14 nmol/l for nifedipine; 0.87 and 1.4 micromol/l for mibefradil, and 0.35 micromol/l and 1.8 nmol/l for efonidipine, respectively. Efonidipine, a dihydropyridine analogue, showed high affinity to T-type Ca2+ channel.