Mibefradil, A T-type calcium channel antagonist in Y1 cells

The effect of mibefradil, a new nondihydropyridine Ca2+ channel antagonist, was investigated on Y1 cells which exhibited T-and L-type Ca2+ currents. I n the great majority of these cells, mibefradil rapidly and selectively blo cked T-type Ca current in a dose-dependent manner with a half maximum actio n at 10-7 M. Furthermore, the specific L-type Ca2+ channel inhibitor, nifed ipine, blocked the Ca2+ inward current remaining after the action of mibefr adil. Mibefradil does not modify the voltage-dependent characteristics of t he current/voltage relationship. However, mibefradil is more effective at d epolarized membrane potential.