Electrophysiological effects of IQM-266 on KV1.5 channels

Abstract

The outward potassium current IKur is the main responsible of the atrial repolarization process and it is generated by the activation of KV1.5 channels, widely expressed in human atria. It is known that mutations in KCNA5 gene, which induce both gain- and loss-of-function in KV1.5 channel, enhance atrial fibrillation susceptibility. Thus, these channels represent a pharmacological target for the development of antiarrhythmic drugs useful in the treatment of supraventricular arrhythmias. KV1.5 channels assembly with several regulatory subunits such as KVβ and KChIPs (KV Channel Interacting Proteins). It has been described that KChIP2 physically interacts with KV1.5 and reduces KV1.5 cell surface expression levels. Our research group has demonstrated that IQM-266 inhibits the current generated by the activation of KV4.3 and KV4.3/KChIP2, being the effects more marked when KChIP2 is present. The aim of the present study is to analyze the effects of IQM-266 on KV1.5 channels. In order to achieve these objectives, HEK293 cells transiently expressing KV1.5 were used. Currents were recorded using the whole-cell configuration of the patch-clamp technique. The effects of IQM-266 on KV1.5 currents were concentration-dependent with an IC50 of 11 μM (n=24). Block induced by IQM-266 (20 μM) sharply increased within the membrane voltage range of the channel activation, arising a maximum degree of block at +20 mV that remained constant at more positive membrane potentials. This compound at 20 μM produced a timedependent block, inducing a: 1) faster inactivation (τ = 305.8±47.6 ms vs. 168.0±13.4 ms, in the absence and in the presence of IQM-266, respectively, n=9, p<0.01), and 2) slower deactivation kinetics, increasing the contribution of the slow component of deactivation to the total process (0.36±0.05 vs. 0.57±0.05, in the absence and in the presence of IQM-266, respectively, n=11, p<0.01). These results are consistent with an open channel block mechanism. Finally, IQM-266 (20 μM) enhanced the degree of use-dependent block of the current (25.6±2.7% vs. 77.6±4.9%, in the absence and in the presence of IQM-266, n=5, p<0.001). These phenomenon was explained by a slowing of the recovery process in the presence of the compound (991.1±131.8 ms vs. 5132.8±763.6 ms in the absence and in the presence of IQM-266, respectively, n=4, p<0.05). Thus, IQM-266 is able to bind KV1.5 channels, although with less affinity than that shown in KV4.3/KChIP2 complexes.