Isoform-specific Prolongation of Kv7 (KCNQ) Potassium Channel Opening Mediated by New Molecular Determinants for Drug-Channel Interactions

Zhaobing Gao,Tangzhi Zhang,Meng Wu,Qiaojie Xiong,Haiyan Sun,Yinan Zhang,Liansuo Zu,Wei Wang,Min Li

doi:10.1074/jbc.m110.116392

Zhaobing Gao, Tangzhi Zhang + Show 7 more

Open Access

https://doi.org/10.1074/jbc.m110.116392

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Abstract

Kv7 channels, especially Kv7.2 (KCNQ2) and Kv7.3 (KCNQ3), are key determinants for membrane excitability in the brain. Some chemical modulators of KCNQ channels are in development for use as anti-epileptic drugs, such as retigabine (D-23129, N-(2-amino-4-(4-fluorobenzylamino)-phenyl)), which was recently approved for clinical use. In addition, several other compounds were also reported to potentiate activity of the Kv7 channels. It is therefore of interest to investigate compound-channel interactions, so that more insights may be gained to aid future development of therapeutics. We have conducted a screen of 20,000 compounds for KCNQ2 potentiators using rubidium flux combined with atomic absorption spectrometry. Here, we report the characterization of a series of new structures that display isoform specificity and induce a marked reduction of deactivation distinct from that of retigabine. Furthermore, KCNQ2(W236L), a previously reported mutation that abolishes sensitivity to retigabine, remains fully sensitive to these compounds. This result, together with mutagenesis and other studies, suggests that the reported compounds confer a unique mode of action and involve new molecular determinants on the channel protein, consistent with the idea of recognizing a new site on channel protein.

Highlights

Conductance, calcium-gated potassium channel (BK), which is normally activated by a combination of membrane depolarization and elevated intracellular calcium, may be activated by high concentrations of calcium alone, at the resting potential, without depolarization [5, 6]
Earlier evidence suggests that KCNQ2 to KCNQ5 are neuronal isoforms [17,18,19,20], whereas KCNQ1 is a non-neuronal isoform, found primarily in cardiac myocytes mediating IKs current upon coassembly with non-conductive accessory KCNE1 subunits [17, 21, 22]
62.5 ms and 3,230.5 Ϯ 534.1 ms (n ϭ 6), respectively (Fig. 3B). work revealed that two leucine residues in S5 (Leu249) and We studied the effects of ztz240 on deactivation at dif- S5-S6 linker (Leu275) of KCNQ2 are key determinants for the ferent voltages

Summary

Introduction

Conductance, calcium-gated potassium channel (BK), which is normally activated by a combination of membrane depolarization and elevated intracellular calcium, may be activated by high concentrations of calcium alone, at the resting potential, without depolarization [5, 6]. Neuronal Kv7 (or KCNQ) channels are activated at subthreshold membrane potentials. Drug-induced potentiation of channel activity (i.e. increase of net current flow in a given time period) may be achieved by several mechanisms, including modulation of protein expression, channel gating, or single channel conductance. A number of compounds have been reported to display potentiating activities on KCNQ channels (e.g. see a recent review [10]). Rubidium (Rbϩ) and thallium (Tlϩ) are two surrogate, heavy metal ions that permeate through most potassium channels Because they are non-physiological ions, they allow improved signal-to-noise ratios in flux assays [27, 28]

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