Strong Activation of ether-à-go-go-Related Gene 1 K⁺ Channel Isoforms by NS1643 in Human Embryonic Kidney 293 and Chinese Hamster Ovary Cells

Abstract

Two different mechanisms leading to increased current have been described for the small-molecule human ether-à -go-gorelated gene (herg) activator NS1643 [1,3-bis-(2-hydroxy-5-trifluoromethylphenyl)-urea]. On herg1a channels expressed in Xenopus laevis oocytes, it mainly acts via attenuation of inactivation and for rat (r) erg1b channels expressed in human embryonic kidney (HEK)-293 cells, it strongly shifts the activation curve to the left. We now investigated the NS1643 effects on erg1b channels in more detail and performed comparative experiments with rat and human erg1a in different expression systems. Significant differences were observed between expression systems, but not between the rat and human isoform. In HEK-293 or Chinese hamster ovary (CHO) cells, activation of rat erg1b channels occurred in a dose-dependent manner with a maximum current increase of 300% obtained with 10 M NS1643. In contrast, the NS1643-induced strong leftward shift in the voltage dependence of activation further increased with higher drug concentration, needed more time to develop, and exhibited use dependence. Coexpression of KCNE1 or KCNE2 did not attenuate this NS1643 effect on erg1 channel activation and did thus not mimic the lower drug potency on this parameter observed in oocytes. NS1643 (10 M) slowed erg1b channel deactivation and recovery from inactivation without significant changes in activation and inactivation kinetics. With the exception of accelerated activation, NS1643 affected erg1a channels similarly, but the effect was less pronounced than in erg1b or erg1a/1b channels. It is noteworthy that rerg1b and herg1a inactivation estimated from fully activated current voltage relationships were unaltered in the continued presence of 10 M NS1643 in the mammalian expression systems, indicating qualitative differences from NS1643 effects in X. laevis oocytes.

The Human Ether-A-Go-Go–Related Gene Activator NS1643 Enhances Epilepsy-Associated KCNQ Channels

“…2, D and E) and leftshifted the I tail (tail current)-V curve largely with V 1/2 values shifting from 25.46 6 1.42 to 252.47 6 1.21 mV (Fig. 2F), which was similar to the observation in other mammalian expression systems, such as human embryonic kidney 293 cells (Casis et al, 2006;Schuster et al, 2011), but different from that in Xenopus laevis oocytes (Hansen et al, 2006). (Gao et al, 2010).…”

“…Noticeable differences in the effects of NS1643 on hERG channels were observed depending on expression systems (Casis et al, 2006;Hansen et al, 2006;Schuster et al, 2011;Durdagi et al, 2012). Thus, potentiation effects of NS1643 on hERG channels expressed in CHO-K1 cells, the transient expression system we used in this study, were characterized first.…”

Deciphering hERG channels: Molecular basis of the rapid component of the delayed rectifier potassium current

“…Also hERG activators are reported to show differential effects in hERG1a compared to hERG1a/1b channels [44,45]. One example is I Kr enhancer NS1643 that showed slightly less pronounced effects on rat ERG1a channels compared to rat ERG1b channels [45]. Important to mention is that the magnitude of the effect was dependent on the expression system used (oocytes vs. HEK or CHO cells).…”

“…Different potency will logically have consequences for prolongation of the AP and arrhythmia risk. Also hERG activators are reported to show differential effects in hERG1a compared to hERG1a/1b channels [44,45]. One example is I Kr enhancer NS1643 that showed slightly less pronounced effects on rat ERG1a channels compared to rat ERG1b channels [45].…”

HERG1 channel agonists and cardiac arrhythmia

“…PD-307243 slowed the rate inactivation and increased hERG tail currents by 3.4-fold at 10 μM, but had no effect on rates of channel activation or deactivation [27] [28]. NS1643 induced a maximum 300% increase in hERG1 at 10 μM, accelerated the rate of activation and shifted V 0.5 for activation by −27 mV [29]. The shift in V 0.5 develops slowly over time and in oocytes, only occurs at much higher drug concentrations [28] [30].…”