Background and PurposeCannabidiol (CBD) is used clinically as an anticonvulsant. Its precise mechanism of action has remained unclear. CBD was recently demonstrated to enhance the activity of the neuronal K(V)7.2/7.3 channel, which may be one important contributor to CBD anticonvulsant effect. Curiously, CBD inhibits the closely related cardiac K(V)7.1/KCNE1 channel. Whether and how CBD affects other K(V)7 subtypes remains uninvestigated and the CBD interaction sites mediating these diverse effects remain unknown. Experimental ApproachHere, we used electrophysiology, molecular dynamics simulations, molecular docking and site-directed mutagenesis to address these questions. Key ResultsWe found that CBD modulates the activity of all human K(V)7 subtypes and that the effects are subtype dependent. CBD enhanced the activity of K(V)7.2-7.5 subtypes, seen as a V-50 shift towards more negative voltages or increased maximum conductance. In contrast, CBD inhibited the K(V)7.1 and K(V)7.1/KCNE1 channels, seen as a V-50 shift towards more positive voltages and reduced conductance. In K(V)7.2 and K(V)7.4, we propose a CBD interaction site at the subunit interface in the pore domain that overlaps with the interaction site of other compounds, notably the anticonvulsant retigabine. However, CBD relies on other residues for its effects than the conserved tryptophan that is critical for retigabine effects. We propose a similar, though not identical CBD site in K(V)7.1, with a non-conserved phenylalanine being important. Conclusions and ImplicationsWe identify novel targets of CBD, contributing to a better understanding of CBD clinical effects and provide mechanistic insights into how CBD modulates different K(V)7 subtypes.

The K(V)7.4 and K(V)7.5 subtypes of voltage -gated potassium channels play a role in important physiological processes such as sound amplification in the cochlea and adjusting vascular smooth muscle tone. Therefore, the mechanisms that regulate K(V)7.4 and K(V)7.5 channel function are of interest. Here, we study the effect of polyunsaturated fatty acids (PUFAs) on human K(V)7.4 and KV7.5 channels expressed in Xenopus oocytes. We report that PUFAs facilitate activation of hK(V)7.5 by shifting the V50 of the conductance versus voltage (G(V)) curve toward more negative voltages. This response depends on the head group charge, as an uncharged PUFA analogue has no effect and a positively charged PUFA analogue induces positive V-50 shifts. In contrast, PUFAs inhibit activation of hK(V)7.4 by shifting V-50 toward more positive voltages. No effect on V-50 of hK(V)7.4 is observed by an uncharged or a positively charged PUFA analogue. Thus, the hK(V)7.5 channels response to PUFAs is analogous to the one previously observed in hK(V)7.1-7.3 channels, whereas the hK(V)7.4 channel response is opposite, revealing subtype-specific responses to PUFAs. We identify a unique inner PUFA interaction site in the voltage-sensing domain of hKV7.4 underlying the PUFA response, revealing an unconventional mechanism of modulation of hK(V)7.4 by PUFAs.

Voltage-gated potassium channels of the K(V)7 family are expressed in many tissues. The physiological importance of K(V)7 channels is evident from specific forms of disorders linked to dysfunctional K(V)7 channels, including variants of epilepsy, cardiac arrhythmia and hearing impairment. Thus, understanding how K(V)7 channels are regulated in the body is of great interest. This Mini Review focuses on the effects of polyunsaturated fatty acids (PUFAs) on K(V)7 channel activity and possible underlying mechanisms of action. By summarizing reported effects of PUFAs on K(V)7 channels and native K(V)7-mediated currents, we conclude that the generally observed effect is a PUFA-induced increase in current amplitude. The increase in current is commonly associated with a shift in the voltage-dependence of channel opening and in some cases with increased maximum conductance. Auxiliary KCNE subunits, which associate with K(V)7 channels in certain tissues, may influence PUFA effects, though findings are conflicting. Both direct and indirect activating PUFA effects have been described, direct effects having been most extensively studied on K(V)7.1. The negative charge of the PUFA head-group has been identified as critical for electrostatic interaction with conserved positively charged amino acids in transmembrane segments 4 and 6. Additionally, the localization of double bonds in the PUFA tail tunes the apparent affinity of PUFAs to K(V)7.1. Indirect effects include those mediated by PUFA metabolites. Indirect inhibitory effects involve K(V)7 channel degradation and re-distribution from lipid rafts. Understanding how PUFAs regulate K(V)7 channels may provide insight into physiological regulation of K(V)7 channels and bring forth new therapeutic strategies.