Mechanism of Block and Identification of the Verapamil Binding Domain to HERG Potassium Channels

Abstract

Calcium channel antagonists have diverse effects on cardiac electrophysiology. We studied the effects of verapamil, diltiazem, and nifedipine on HERG K+ channels that encode IKr in native heart cells. In our experiments, verapamil caused high-affinity block of HERG current (IC50=143.0 nmol/L), a value close to those reported for verapamil block of L-type Ca2+ channels, whereas diltiazem weakly blocked HERG current (IC50=17.3 micromol/L), and nifedipine did not block HERG current. Verapamil block of HERG channels was use and frequency dependent, and verapamil unbound from HERG channels at voltages near the normal cardiac cell resting potential or with drug washout. Block of HERG current by verapamil was reduced by lowering pHO, which decreases the proportion of drug in the membrane-permeable neutral form. N-methyl-verapamil, a membrane-impermeable, permanently charged verapamil analogue, blocked HERG channels only when applied intracellularly. Verapamil antagonized dofetilide block of HERG channels, which suggests that they may share a common binding site. The C-type inactivation-deficient mutations, Ser620Thr and Ser631Ala, reduced verapamil block, which is consistent with a role for C-type inactivation in high-affinity drug block, although the Ser620Thr mutation decreased verapamil block 20-fold more than the Ser631Ala mutation. Our findings suggest that verapamil enters the cell membrane in the neutral form to act at a site within the pore accessible from the intracellular side of the cell membrane, possibly involving the serine at position 620. Thus, verapamil shares high-affinity HERG channel blocking properties with other class III antiarrhythmic drugs, and this may contribute to its antiarrhythmic mechanism.

Dihydropyridine Ca2+ channel antagonists and agonists block Kv4.2, Kv4.3 and Kv1.4 K+ channels expressed in HEK293 cells

“…These results suggest that the delayed rectifier channels in cardiac myocytes may not be clinical targets for DHPs. Moreover, neither fast nor slow components of cardiac-delayed rectifier K + currents (I Kr and I Ks ) are susceptible to DHPs at therapeutic doses (Daleau et al, 1997;Zhang et al, 1999). It is noteworthy that 1 mM nicardipine reduced by 50% the peak Kv4.3L currents activated by 200 ms depolarization from À80 to +20 mV at 1 Hz.…”

Comparison of the effects of antiarrhythmic drugs flecainide and verapamil on fKv1.4ΔN channel currents in Xenopus oocytes

“…Verapamil shares these characteristics. our results demonstrate that flecainide and verapamil exhibit similar affinities for fKv1.4ΔN, but the drugs do not share high-affinity heRG channel blocking properties [21] . Because flecainide and verapamil are different types of antiarrhythmic drugs, we examined the electrophysiological effects of both drugs on fKv1.4ΔN channel inactivation.…”

“…Flecainide may inhibit the wild-type Kv4.2 channel (Kv4.2WT) currents in a concentration-dependent manner, and it has been shown to induce a voltage-dependent block of hERG channels [19,20] . In addition, verapamil has been reported to produce a potent use-and frequency-dependent block of hERG channels [21] and to inhibit the hKv1.5 channel in low micromolar concentrations [22] . Flecainide and verapamil have been shown recently to inhibit the conductance of Kv1.4 channels expressed in Xenopus oocytes [13,23] .…”

A Simple Protocol for the Myocardial Differentiation of Human iPS Cells

“…Both E-4031 (an Ikr channel blocker) and chromanol 293B (an Iks channel blocker) decreased the beat counts in our EBs. Verapamil blocks the calcium and Ikr channels, 14) and increases the beat count at low concentrations that shorten the plateau phase (phase-2 action potential) of the action potential by inhibiting calcium channels, and decreases it at high concentrations that may inhibit the Ikr channels. Pentamidin decreases the Ikr channel expression on the cell membrane due to the inhibition of the Ikr channel trafficking.…”