The endocannabinoid ARA-S displays variably activating effects on Kv7.1/KCNE1 carrying long QT syndrome mutations.

Abstract

The cardiac arrhythmia long QT syndrome (LQTS) is characterized by a delayed ventricular repolarization. The most common cause of inherited LQTS is loss-of-function mutations in the KV7.1/KCNE1 channel. Therefore, the KV7.1/KCNE1 channel is an interesting target for developing new antiarrhythmic drugs, which ideally would restore the function of mutated KV7.1/KCNE1 channels. In this study, we evaluate the endogenous endocannabinoid-like compound ARA-S as an activator of the human KV7.1/KCNE1 channel carrying diverse loss-of-function mutations linked to LQTS. Using the two-electrode voltage clamp technique, we have previously found ARA-S to facilitate activation of the wild type KV7.1/KCNE1 channel expressed in Xenopus oocytes, seen as a left-shift in voltage dependence of channel opening and a conductance increase. Moreover, we have previously shown that ARA-S restores a physiological QT interval in isolated guinea pig hearts suffering from drug-induced LQTS. Hence, ARA-S is an interesting endogenous KV7.1/KCNE1 channel modulator which may inspire drug development. Now, using the same technique on LQTS-mutated KV7.1/KCNE1 channels, we find that ARA-S facilitates activation of all tested mutants, but the magnitude of the effect varies among them. For instance, the effect of ARA-S is reduced on the mutant I204F but increased on the mutant A370V, compared to the effect on the wild-type channel. This suggests that the effect of the compound is dependent on the genetic background. To better understand its impact, we group the tested mutants based on their response to ARA-S and factors such as whether they are localized to putative ARA-S binding sites or other interesting sites, such as PIP2 sites. Altogether, this work finds ARA-S as an efficient activator of LQTS-associated mutant KV7.1/KCNE1 channels and is a first step towards understanding how the genetic background determines the effect of this modulator.