Combining endocannabinoids with retigabine for enhanced M-channel effect and improved K(V)7 subtype selectivity

Retigabine is unique among anticonvulsant drugs by targeting the neuronal M-channel, which is composed of K(V)7.2/K(V)7.3 and contributes to the negative neuronal resting membrane potential. Unfortunately, retigabine causes adverse effects, which limits its clinical use. Adverse effects may be reduced by developing M-channel activators with improved K(V)7 subtype selectivity. The aim of this study was to evaluate the prospect of endocannabinoids as M-channel activators, either in isolation or combined with retigabine. Human K(V)7 channels were expressed in Xenopus laevis oocytes. The effect of extracellular application of compounds with different properties was studied using two-electrode voltage clamp electrophysiology. Site-directed mutagenesis was used to construct channels with mutated residues to aid in the mechanistic understanding of these effects. We find that arachidonoyl-L-serine (ARA-S), a weak endocannabinoid, potently activates the human M-channel expressed in Xenopus oocytes. Importantly, we show that ARA-S activates the M-channel via a different mechanism and displays a different K(V)7 subtype selectivity compared with retigabine. We demonstrate that coapplication of ARA-S and retigabine at low concentrations retains the effect on the M-channel while limiting effects on other K(V)7 subtypes. Our findings suggest that improved K(V)7 subtype selectivity of M-channel activators can be achieved through strategically combining compounds with different subtype selectivity.