Electrophysiological and Pharmacological Characterization of Human Inwardly Rectifying K_ir2.1 Channels on an...

Inwardly rectifying I_K1 potassium currents of the heart control the resting membrane potential of ventricular cardiomyocytes during diastole and contribute to their repolarization after each action potential. Mutations in the gene encoding K_ir2.1 channels, which primarily conduct ventricular I_K1, are associated with inheritable forms of arrhythmias and sudden cardiac death. Therefore, potential iatrogenic inhibition of K_ir2.1-mediated I_K1 currents is a cardiosafety concern during new drug discovery and development. K_ir2.1 channels are part of the panel of cardiac ion channels currently considered for refined early compound risk assessment within the Comprehensive in vitro Proarrhythmia Assay initiative. In this study, we have validated a cell-based assay allowing functional quantification of K_ir2.1 inhibitors using whole-cell recordings of Chinese hamster ovary cells stably expressing human K_ir2.1 channels. We reproduced key electrophysiological and pharmacological features known for native I_K1, including current enhancement by external potassium and voltage- and concentration-dependent blockade by external barium. Furthermore, the K_ir inhibitors ML133, PA-6, and chloroquine, as well as the multichannel inhibitors chloroethylclonidine, chlorpromazine, SKF-96365, and the class III antiarrhythmic agent terikalant demonstrated slowly developing inhibitory activity in the low micromolar range. The robustness of this assay authorizes medium throughput screening for cardiosafety purposes and could help to enrich the currently limited K_ir2.1 pharmacology.