IQM-22110, a new selective inhibitor of KChIP3 and its electrophysiological effects on Kv4.3, Kv4.3/KChIP3 and Kv4.3/KChIP2 currents

Kv4 channels generate rapidly activating and inactivating outward currents responsible for the repolarization of both cardiac and neuronal action potentials through ITO (transient outward current) and IA (A-type K+ current), respectively. Kv4 dysfunctions have been identified in both cardiac and neuronal diseases (Brugada syndrome, atrial fibrillation, epilepsy or Alzheimer's disease). However, Kv4 channels need to assemble with regulatory subunits to fully reproduce ITO and IA currents. Among them, we will focus on KChIPs (potassium channel interacting proteins), being KChIP3 predominant in the brain and KChIP2 in both brain and heart. The assembly of these regulatory subunits not only modulates the biophysical properties of the channel, but also its pharmacology. For this reason, we have analysed the electrophysiological effects of IQM-22110 (a novel KChIP3 ligand) on the currents generated by Kv4.3, Kv4.3/KChIP3 and Kv4.3/KChIP2 channels. CHO cells were transiently transfected, and the potassium currents were recorded using the whole-cell patch-clamp technique. Our results indicate that IQM-22110 exerts differential effects on these currents, being the concentration-dependence of inhibition modified, exhibiting a biphasic curve when KChIP3 is present, thus suggesting two binding sites for IQM-22110 in this complex. With molecular dynamics and site-directed mutagenesis, we have identified the binding pocket corresponding to the high affinity site. Also, we have demonstrated that IQM-22110 binds to the closed-active state of the channel. In this study: i) IQM-22110 has proven to be a selective inhibitor of Kv4.3/KChIP3 at low concentrations, and ii) a new binding pocket for selective KChIP3/Kv4.3 ligands has been identified.