Received for publication July 11, 2007.
Revised October 13, 2007.
Accepted for publication October 15, 2007.

The investigational anticonvulsant lacosamide selectively enhances slow inactivation of voltage-gated sodium channels

Abstract

Our hypothesis was that lacosamide modulates voltage-gated sodium channels (VGSCs) at clinical concentrations (32-100µM). Lacosamide reduced spiking evoked in cultured rat cortical neurons by 30s depolarising ramps but not by 1s ramps. Carbamazepine and phenytoin reduced spike firing induced by both ramps. Lacosamide inhibited sustained repetitive firing during a 10 s burst but not within the first second. Tetrodotoxin-sensitive VGSC currents in N1E-115 cells were reduced by 100 µM lacosamide, carbamazepine, lamotrigine and phenytoin from V_h: -60 mV. Hyperpolarization (500 ms) to -100 mV removed the block by carbamazepine, lamotrigine and phenytoin but not by lacosamide. The voltage dependence of activation was not changed by lacosamide. The inactive S-stereoisomer did not inhibit VGSCs. Steady state fast inactivation curves were shifted in the hyperpolarizing direction by carbamazepine, lamotrigine and phenytoin but not at all by lacosamide. Lacosamide did not retard recovery from fast inactivation in contrast to carbamazepine. Carbamazepine, lamotrigine and phenytoin but not lacosamide all produced frequency-dependent facilitation of block of a 3 s, 10 Hz pulse train. Lacosamide shifted the slow inactivation voltage curve in the hyperpolarizing direction and significantly promoted the entry of channels into the slow inactivated state (carbamazepine weakly impaired entry into the slow inactivated state) without altering the rate of recovery. Lacosamide is the only analgesic/anticonvulsant drug that reduces VGSC availability by selective enhancement of slow inactivation but without apparent interaction with fast inactivation gating. The implications of this unique profile are being explored in phase III clinical trials for epilepsy and neuropathic pain.

Key words: Ion channel regulation, Sodium, Antiarrhythmic drugs, Local anesthetics, Func. analysis receptor/ion channel mutants

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