Ilepcimide inhibited sodium channel activity in mouse hippocampal neurons

Ilepcimide (ICM), a clinically effective antiepileptic drug, has been used in China for decades; however, its antiepileptic mechanism remains unclear. ICM is structurally similar to antiepileptic drug lamotrigine (LTG). LTG exerts its anticonvulsant effect by inhibiting voltage-gated Na⁺ channel (Na_V) activity. Thus it is speculated that ICM also exert its antiepileptic activity by inhibiting sodium channel activity. We studied the inhibition of Na_V activity by ICM in acutely isolated mouse hippocampal pyramidal neurons. We evaluated ICM-mediated tonic, concentration-dependent, and voltage-dependent inhibition of Na_V, and the effects of ICM and LTG on Na_V biophysical properties. Na⁺ currents in hippocampal pyramidal neurons were tonically inhibited by ICM in a concentration- and voltage-dependent manner. The half-maximal inhibitory concentration (IC₅₀) of ICM at a holding potential (V_h) of -90 mV was higher than that at a V_h of -70 mV. Compared with the control groups, in the presence of 10 μM ICM, the current densities of Na⁺ channels were reduced, the half-maximal availability of the inactivation curve (V_1/2) was shifted to more negative potentials, and the recovery from inactivation was delayed. These data can contribute to further investigation of the inhibitory effect of ICM on the sodium channel, suggesting that the main reason for the anticonvulsant effect of ICM is the small influx of sodium ions. ICM can prevent abnormal discharge of neurons, which may prevent epilepsy.