Molecular determinants of Kv1.5 channel block by diphenyl phosphine oxide-1

Abstract 

Kv1.5 channels conduct the ultra-rapid delayed rectifier current (I_Kur) that contributes to action potential repolarization of human atrial myocytes. Block of these channels has been proposed as a treatment for atrial arrhythmias. Diphenyl phosphine oxide-1 (DPO-1) is a novel and potent inhibitor of Kv1.5 potassium channels. The present study was undertaken to characterize the mechanisms and molecular determinants of channel block by DPO-1. Experiments were carried out on wild-type and mutant Kv1.5 channels expressed in Xenopus laevis oocytes using the standard two microelectrode voltage clamp technique. DPO-1 blocked Kv1.5 current in oocytes with an IC₅₀ of 0.78±0.12μM at +40mV. Block was enhanced by higher rates of stimulation, consistent with preferential binding of the drug to the open state of the channel. Ala-scanning mutagenesis of the pore domain of Kv1.5 identified the residues Thr480, Leu499, Leu506, Ile508, Leu510 and Val514 as components of the putative binding site for DPO-1, partially overlapping the site previously defined for the Kv1.5 channel blockers AVE0118 and S0100176. Block of Kv1.5 by DPO-1 was significantly reduced in the presence of Kvβ1.3.

Abbreviations: DPO-1, diphenylphosphine oxide-1, APD, action potential duration, I_Kr, rapid delayed rectifier K⁺ current, I_Ks, slow delayed rectifier K⁺ current, I_Kur, ultra-rapid delayed rectifier current, IC₅₀, the concentration of drug required for 50% block of current

Keywords: Potassium channels, Ultra-rapid delayed rectifier, Kv1.5, Voltage clamp, Diphenyl phosphine oxide-1, Atrial fibrillation