Characterization of recombinant human cardiac KCNQI/KCNE1 channels (IKs) stably expressed in HEK 293 cells

The present study was designed to characterize pharmacological, biophysical and electrophysiological properties of the recombinant human cardiac I-Ks (KCNQ1/KCNE1) channels at physiological temperature. Human cardiac KCNQ1 and KCNE1 genes were cotransfected into HEK 293 cells, and a cell clone stably expressing both genes was selected. Membrane currents were recorded using a perforated patch-clamp technique. The typical IKs was slowly activated upon depolarization voltages in HEK 293 cells stably expressing human cardiac KCNQ1 and KCNE1 genes, and the current was inhibited by IKs blockers HMR 1556 and chromanol 29313, with 50% inhibitory concentrations (IC(50)s) Of 83.8 nm and 9.2 mu M, respectively. IKs showed a significant temperature-dependent increase in its magnitude upon elevating bath temperature to 36 degrees C from room temperature (21 degrees C). The current was upregulated by the beta-adrenoceptor agonist isoproterenol, and the effect was reversed by H89. In addition, I-Ks was inhibited by Ba2+ in a concentration-dependent manner (IC50 = 1.4 mm). Action potential clamp revealed a "bell-shaped" time course of I-Ks during the action potential, and maximal peak current was seen at the plateau of the action potential. A significant use- and frequency-dependent increase of I-Ks was observed during a train of action potential clamp. These results indicate that the recombinant human cardiac I-Ks stably expressed in HEK 293 cells is similar to native IKs in drug sensitivity and regulated by Ba2+ and beta-adrenoceptor via the cyclic adenosine monophosphate/protein kinase A pathway. Importantly, the current exhibits significant temperature dependence, a bell-shaped time course during action potential and prominent use- or frequency-dependent accumulation during a train of action potentials.