V102862 (Co 102862): a potent, broad-spectrum state-dependent blocker of mammalian voltage-gated sodium channels

摘要

1 4-(4-Fluorophenoxy)benzaldehyde semicarbazone (V102862) was initially described as an orally active anticonvulsant with robust activity in a variety of rodent models of epilepsy. The mechanism of action was not known. We used whole-cell patch-clamp techniques to study the effects of V102862 on native and recombinant mammalian voltage-gated Na~+ channels. 2 V102862 blocked Na~+ currents (I_(Na)) in acutely dissociated cultured rat hippocampal neurons. Potency increased with membrane depolarization, suggesting a state-dependent mechanism of inhibition. There was no significant effect on the voltage dependence of activation of I_(Na). 3 The dissociation constant for the inactivated state (K_I) was ～0.6μM, whereas the dissociation constant for the resting state (K_R) was > 15μM. 4 The binding to inactivated channels was slow, requiring a few seconds to reach steady state at -80 mV. 5 The mechanism of inhibition was characterized in more detail using human embryonic kidney-293 cells stably expressing rat brain type IIA Na~+ (rNa_v1.2) channels, a major Na~+ channel α subunit in rat hippocampal neurons. Similar to hippocampal neurons, V102862 was a potent state-dependent blocker of rNa_v1.2 channels with a K_I of ～0.4μM and K_R ～30μM. V102862 binding to inactivated channels was relatively slow (k_+ approx= l.7μM~(-1) s~(-1)). V102862 shifted the steady-state availability curve in the hyperpolarizing direction and significantly retarded recovery of Na~+ channels from inactivation. 6 These results suggest that inhibition of voltage-gated Na~+ channels is a major mechanism underlying the anticonvulsant properties of V102862. Moreover, understanding the biophysics of the interaction may prove to be useful in designing a new generation of potent Na~+ channel blocker therapeutics.