Hexachlorophene is a potent KCNQ1/KCNE1 potassium channel activator which rescues LQTs mutants

Abstract

The voltage-gated KCNQ1 potassium channel is expressed in cardiac tissues, and coassembly of KCNQ1 with an auxiliary KCNE1 subunit mediates a slowly activating current that accelerates the repolarization of action potential in cardiomyocytes. Mutations of KCNQ1 genes that result in reduction or loss of channel activity cause prolongation of repolarization during action potential, thereby causing long QT syndrome (LQTs). Small molecule activators of KCNQ1/KCNE1 are useful both for understanding the mechanism of the complex activity and for developing therapeutics for LQTs. In this study we report that hexachlorophene (HCP), the active component of the topical anti-infective prescription drug pHisoHex, is a KCNQ1/KCNE1 activator. HCP potently increases the current amplitude of KCNQ1/KCNE1 expressed by stabilizing the channel in an open state with an EC(50) of 4.61 ± 1.29 μM. Further studies in cardiomyocytes showed that HCP significantly shortens the action potential duration at 1 μM. In addition, HCP is capable of rescuing the loss of function of the LQTs mutants caused by either impaired activation gating or phosphatidylinositol-4,5-bisphosphate (PIP2) binding affinity. Our results indicate HCP is a novel KCNQ1/KCNE1 activator and may be a useful tool compound for the development of LQTs therapeutics.

Figure 1. Chemical structures of reported KCNQ1 or KCNQ1/KCNE1 activators and HCP.

R-L3 and ZnPy potentiate the KCNQ1 but not the KCNQ1/KCNE1 complex. DIDS and MFA strongly potentiate the KCNQ1/KCNE1 complex but exhibit little effect on the homomeric KCNQ1. PBA potentiates both the KCNQ1 and the KCNQ1/KCNE1 complex.

Figure 2. Subtype selectivity of HCP.

For all tested channels, the holding potential was set at −100 mV and the currents were elicited by a depolarization step to −10 mV.

Figure 3. Effects of HCP on the homomeric KCNQ1 channel.

A. Representative traces of the homomeric KCNQ1 channel in the absence and presence of 10 μM HCP. B. The normalized inactivation phase from full traces in the absence (black line) and presence (gray line) of 10 μM HCP. The testing depolarization is +50 mV. C. The normalized tail current from full traces in the absence (black line) and presence (gray line) of 10 μM HCP. The tailed currents were elicited by a hypolarization step to −120 mV followed the +50 mV depolarization. D. Histogram summarized the effects of 10 μM HCP on inactivation and deactivation of KCNQ1 (n≥3, ***p<0.001 versus control). E. G-V curves in the absence (filled circle) and presence (open circle) of 10 μM HCP (n≥3).

Figure 4. Effects of HCP on the KCNQ1/KCNE1 complex.

A. Representative traces of the KCNQ1/KCNE1 complex in the absence and presence of 10 μM HCP. The holding potential was set at −100 mV. The currents were elicited by a series of depolarization from −90 mV to +80 mV. B. G-V curves of the KCNQ1/KCNE1 complex. C. Potentiation of 10 μM HCP on outward currents of the KCNQ1/KCNE1. I/I ₀, I, and I ₀ are same as being referred in Table 1. D. Dose-response curve of HCP on the KCNQ1/KCNE1 complex. n≥3 of each data point.

Figure 5. Effects of HCP on the action potential recorded in cardiomyocytes.

A. Representative traces of IKs before and after application of 1μM HCP. To elicit the IKs, a series of depolarization steps from −70 mV to +70 mV in 10 mV increments were applied. B. Effects of 1 μM HCP on amplitude of IKs measured at +50 mV. * p<0.05 versus control. C. G-V curves of IKs. D. Effects of R-L3 on action potentials. E. Effects of HCP on action potentials. Chromonal 293B (10 μM) was co-applied with 1 μM HCP after steady state inhibition. F. Histograms show the change of action potential duration after application of R-L3 and HCP.

Figure 6. Effects of HCP on two LQTs mutants.

A. Representative traces of homomeric R243C and R539W with and without 10 μM HCP. B. Representative traces of R243C/KCNE1 and R539W/KCNE1 with and without 10 μM HCP.