Effective Modulation by Lacosamide on Cumulative Inhibition of INa during High-Frequency Stimulation and Recovery of INa Block during Conditioning Pulse Train

Abstract

The effects of lacosamide (LCS, Vimpat®), an anti-convulsant and analgesic, on voltage-gated Na+ current (INa) were investigated. LCS suppressed both the peak (transient, INa(T)) and sustained (late, INa(L)) components of INa with the IC50 values of 78 and 34 μM found in GH3 cells and of 112 and 26 μM in Neuro-2a cells, respectively. In GH3 cells, the voltage-dependent hysteresis of persistent INa (INa(P)) during the triangular ramp pulse was strikingly attenuated, and the decaying time constant (τ) of INa(T) or INa(L) during a train of depolarizing pulses was further shortened by LCS. The recovery time course from the INa block elicited by the preceding conditioning train can be fitted by two exponential processes, while the single exponential increase in current recovery without a conditioning train was adequately fitted. The fast and slow τ’s of recovery from the INa block by the same conditioning protocol arose in the presence of LCS. In Neuro-2a cells, the strength of the instantaneous window INa (INa(W)) during the rapid ramp pulse was reduced by LCS. This reduction could be reversed by tefluthrin. Moreover, LCS accelerated the inactivation time course of INa activated by pulse train stimulation, and veratridine reversed its decrease in the decaying τ value in current inactivation. The docking results predicted the capability of LCS binding to some amino-acid residues in sodium channels owing to the occurrence of hydrophobic contact. Overall, our findings unveiled that LCS can interact with the sodium channels to alter the magnitude, gating, voltage-dependent hysteresis behavior, and use dependence of INa in excitable cells.

Ion Channels as a Potential Target in Pharmaceutical Designs

“…However, because of the multiple therapeutic effects of this drug, additional electrophysiological actions need to be further explored. A recent report by Wu et al [ 3 ] demonstrated that I Na(T) and I Na(L) were differentially suppressed with IC 50 values of 112 and 26 μM, respectively. The hysteretic strength of persistent I Na in response to a triangular ramp pulse was inhibited by LCS exposure.…”

“…Moreover, the fast and slow time constants of recovery from the I Na block by the conditioning pulse-train depolarization were increased. Therefore, the results disclosed that LCS could interact with voltage-gated sodium (Na V ) channels to alter the magnitude, gating, frequency dependence, and voltage-dependent hysteresis of I Na in excitable cells [ 3 ].…”