Activation of Expressed KCNQ Potassium Currents and Native Neuronal M-Type Potassium Currents by the Anti-Convulsant Drug Retigabine

Abstract

Retigabine [D-23129;<i>N</i>-(2-amino-4-(4-fluorobenzylamino)-phenyl) carbamic acid ethyl ester] is a novel anticonvulsant compound that is now in clinical phase II development. It has previously been shown to enhance currents generated by KCNQ2/3 K⁺ channels when expressed in Chinese hamster ovary (CHO) cells (Main et al., 2000;Wickenden et al., 2000). In the present study, we have compared the actions of retigabine on KCNQ2/3 currents with those on currents generated by other members of the KCNQ family (homomeric KCNQ1, KCNQ2, KCNQ3, and KCNQ4 channels) expressed in CHO cells and on the native M current in rat sympathetic neurons [thought to be generated by KCNQ2/3 channels (Wang et al., 1998)]. Retigabine produced a hyperpolarizing shift of the activation curves for KCNQ2/3, KCNQ2, KCNQ3, and KCNQ4 currents with differential potencies in the following order: KCNQ3 &gt; KCNQ2/3 &gt; KCNQ2 &gt; KCNQ4, as measured either by the maximum hyperpolarizing shift in the activation curves or by the EC₅₀ values. In contrast, retigabine did not enhance cardiac KCNQ1 currents. Retigabine also produced a hyperpolarizing shift in the activation curve for native M channels in rat sympathetic neurons. The retigabine-induced current was inhibited by muscarinic receptor stimulation, with similar agonist potency but 25% reduced maximum effect. In unclamped neurons, retigabine produced a hyperpolarization and reduced the number of action potentials produced by depolarizing current injections, without change in action potential configuration.