Retigabine, a novel anti-convulsant, enhances activation of KCNQ2/Q3 potassium channels

Retigabine [N-(2-amino-4-[fluorobenzylamino]-phenyl) carbamic acid; D-23129] is a novel anticonvulsant, unrelated to currently available antiepileptic agents, with activity in a broad range of seizure models. In the present study, we sought to determine whether retigabine could enhance current through M-like currents in PC12 cells and KCNQ2/Q3 K⁺ channels expressed in Chinese hamster ovary cells (CHO-KCNQ2/Q3). In differentiated PC12 cells, retigabine enhanced a linopirdine-sensitive current. The effect of retigabine was associated with a slowing of M-like tail current deactivation in these cells. Retigabine (0.1 to 10 μM) induced a potassium current and hyper-polarized CHO cells expressing KCNQ2/Q3 cells but not in wild-type cells. Retigabine-induced currents in CHO-KCNQ2/Q3 cells were inhibited by 60.6 ± 11% (n = 4) by the KCNQ2/Q3 blocker, linopirdine (10 μM), and 82.7 ± 5.4% (n = 4) by BaCl₂ (10 mM). The mechanism by which retigabine enhanced KCNQ2/Q3 currents involved large, drug-induced, leftward shifts in the voltage dependence of channel activation (-33.1 ± 2.6 mV, n = 4, by 10 μM retigabine). Retigabine shifted the voltage dependence of channel activation with an EC₅₀ value of 1.6 ± 0.3 μM (slope factor was 1.2 ± 0.1, n = 4 to 5 cells per concentration). Retigabine (0.1 to 10 μM) also slowed the rate of channel deactivation, predominantly by increasing the contribution of a slowly deactivating tail current component. Our findings identify KCNQ2/Q3 channels as a molecular target for retigabine and suggest that activation of KCNQ2/Q3 channels may be responsible for at least some of the anticonvulsant activity of this agent.