CP1 Opens IKs Channels by Substituting PIP2

Abstract

The voltage-gated potassium channel KCNQ1 co-assembles with the auxiliary subunit KCNE1 to form the IKs channel in the heart. The IKs current, a slow delayed rectifier K+ current, plays a key role in repolarization of cardiac action potentials. Mutations in the KCNQ1 gene are associated with long QT (LQT) syndrome, atrial fibrillation and short QT syndrome, which lead to cardiac arrhythmias. It was shown that KCNQ1 and IKs channels require PIP2 (Phosphatidylinositol 4,5-bisphosphate) for activation. This lipid acts as a cofactor of the channel for the movements of the voltage sensor domain to trigger the pore gate domain to open. Using the previously identified PIP2 binding site in a homology structural model of KCNQ1 as the target, an in-silico screening of chemical compounds in the Available Chemical Database (ACD, Molecular Design, Ltd.) and a subsequent experminetal testing on the IKs channels expressed in Xenopus oocytes identified CP1 as a novel IKs opener. CP1 increases IKs currents by two-fold and alters voltage dependence and kinetics of activation and deactivation of IKs channels. The potentiation effect of CP1 on IKs currents has an EC50 of 7.4 µM. Consistent with targeting the PIP2 binding site,CP1 rescues the IKs current with the coexpression of CiVSP, which depletes PIP2 and inhibits the currents. The KCNQ1/IKs specific blocker, Chromanol 293B inhibits the enhanced current due to CP1 application, suggesting that CP1 substitutes for PIP2in activating IKs channels. In preliminary experimetns with Guinea-pig ventricular myocytes, CP1 caused similar changes in chromanol sensitive IKs while also shortening action potential duration. CP1 as an opener of the IKs channels may provide a novel therapy to treat congential and acquired LQT syndromes.