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

ABSTRACT In cardiac myocytes, the slow component of the delayed rectifier K + current (I Ks ) ensures repolarization of action potential during beta-adrenergic activation or when other repolarizing K + currents fail. As a key factor of cardiac repolarization I Ks should be present in model species used for cardiovascular drug screening, preferably with pharmacological characteristics similar to those of the human I Ks . To this end, we investigated the effects of inhibitors and activators of the I Ks on KCNQ1 and KCNQ1+KCNE1 channels of the zebrafish, an important model species, in Chinese hamster ovary cells. Inhibitors of I Ks , chromanol 293B and HMR-1556, inhibited zebrafish I Ks channels with approximately similar potency as that of mammalian I Ks . Chromanol 293B concentration for half-maximal inhibition (IC 50 ) of zebrafish I Ks 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 I Ks with IC 50 =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 I Ks activators, both inhibited zebrafish I Ks . R-L3 almost completely inhibited zebrafish I Ks generated by KCNQ1 and KCNQ1+KCNE1 channels with similar affinity (IC 50 1.1±0.4 and 1.0±0.4 μM, respectively). Mefenamic acid partially blocked zebrafish KCNQ1 (IC 50 =9.5±4.8 μM) and completely blocked KCNQ1+KCNE1 channels (IC 50 =3.3±1.8 μM). Although zebrafish I Ks responds to I Ks 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.