Effect of channel assembly (KCNQ1 or KCNQ1 + KCNE1) on the response of zebrafish I_Ks to I_Ks inhibitors and activators

Abstract

In cardiac myocytes, the slow component of the delayed rectifier K+ current (IKs) ensures repolarization of action potential during beta-adrenergic activation or when other repolarizing K+ currents fail. As a key factor of cardiac repolarization IKs should be present in model species used for cardiovascular drug screening, preferably with pharmacological characteristics similar to those of the human IKs. To this end, we investigated the effects of inhibitors and activators of the IKs on KCNQ1 and KCNQ1+KCNE1 channels of the zebrafish, an important model species, in Chinese hamster ovary cells. Inhibitors of IKs, chromanol 293B and HMR-1556, inhibited zebrafish IKs channels with approximately similar potency as that of mammalian IKs. Chromanol 293B concentration for half-maximal inhibition (IC50) of zebrafish IKs was at 13.1±5.8 and 13.4±2.8 μM for KCNQ1 and KCNQ1+KCNE1 channels, respectively. HMR-1556 was a more potent inhibitor of zebrafish IKs with IC50=0.1±0.1 μM and 1.5±0.8 μM for KCNQ1 and KCNQ1+KCNE1 channels, respectively. R-L3 and mefenamic acid, generally identified as IKs activators, both inhibited zebrafish IKs. R-L3 almost completely inhibited zebrafish IKs generated by KCNQ1 and KCNQ1+KCNE1 channels with similar affinity (IC50 1.1±0.4 and 1.0±0.4 μM, respectively). Mefenamic acid partially blocked zebrafish KCNQ1 (IC50=9.5±4.8 μM) and completely blocked KCNQ1+KCNE1 channels (IC50=3.3±1.8 μM). Although zebrafish IKs responds to IKs inhibitors in the same way as mammalian IKs, its response to activators is atypical, probably due to the differences in the binding domain of KCNE1 to KCNQ1. Therefore, care must be taken when translating the results from zebrafish to humans.