TY - JOUR T1 - Characterization of Mibefradil Block of the Human Heart Delayed Rectifier hKv1.5 JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 771 LP - 778 VL - 295 IS - 2 AU - Loïc Perchenet AU - Odile Clément-Chomienne Y1 - 2000/11/01 UR - http://jpet.aspetjournals.org/content/295/2/771.abstract N2 - The goal of this study was to analyze the effects of mibefradil on a human cardiac K+ channel (hKv1.5) stably expressed in Chinese hamster ovary cells using the whole-cell configuration of the patch-clamp technique. Mibefradil inhibited in a concentration-dependent manner the hKv1.5 current with aKD value of 0.78 ± 0.05 μM and a Hill coefficient of 0.97 ± 0.06. Block induced by mibefradil was voltage dependent, consistent with a value of electrical distance of 0.13. The apparent association (k) and dissociation (l) rate constants measured at +50 mV were found to be 7.3 ± 0.5 × 106M−1 · s−1 and 4.3 ± 0.1 s−1, respectively. Block increased rapidly between −20 and +10 mV, coincident with channel opening and suggested an open channel block mechanism, which was confirmed by a slower deactivation time course resulting in a “crossover” phenomenon when tail currents recorded under control conditions and in the presence of mibefradil were superimposed. Shifts toward negative potentials of the maximum conductance and the activation curve were observed, confirming the voltage dependence of block. Mibefradil induced a significant use-dependent block when trains of depolarization at frequencies between 0.02 and 2 Hz were applied. In the presence of mibefradil, recovery of inactivation was faster than under control conditions, suggesting that mibefradil might compete with the inactivation gate of hKv1.5. These results indicate that mibefradil blocks hKv1.5 channels in a concentration-, voltage-, time- and use-dependent manner and the concentrations needed to observe these effects are in the therapeutic range. The American Society for Pharmacology and Experimental Therapeutics ER -