Abstracts

Rationale: Ca_v2.1 calcium (P/Q-type) channels play a prominent role in initiating action-potential-evoked neurotransmitter release at central nervous system synapses and impaired function of brain Ca_v2.1 may have a central role in the pathogenesis of certain cases of primary generalized epilepsy. T-type calcium channels (Ca_v3.2) are critically important in controlling the excitability of the postsynaptic compartment of neurons, both in normal and epileptic neurons. Transcriptional induction of Ca_v3.2 is a critical step in epileptogenesis and neuronal vulnerability. The present study determined the effect of eslicarbazepine acetate's (ESL) major active metabolite eslicarbazepine, R-licarbazepine (a minor metabolite of ESL) and oxcarbazepine (OXC) on human hCa_v2.1 and hCa_v3.2 currents. Methods: The whole-cell patch-clamp technique was used to investigate the effects of eslicarbazepine, R-licarbazepine and OXC on hCa_v2.1 and hCa_v3.2 calcium channels stably expressed in CHO and HEK 293 cells, respectively. Compounds were tested (0.3 to 1000 μM; n=3-5 cells) on hCa_v2.1 and hCa_v3.2 currents upon depolarisation of the cell membrane to -10mV or -25mV for 500 ms or 50ms from a holding potential of -80mV, respectively. Ca_v2.1 and Cav3.2 blockers cobalt chloride, valproic acid and mibefradil were used as reference. Results: Eslicarbazepine, R-licarbazepine and OXC did not markedly affect hCa_v2.1 calcium peak currents, but eslicarbazepine and R-licarbazepine potently inhibited hCa_v3.2 calcium peak currents (figure 1, table 1). The inhibition curves for blockade of hCa_v3.2 calcium peak currents were best fitted with a two site binding model and a constant remaining current amplitude. A block of high affinity occurs with an IC50 of 0.43 μM and 6.54 μM for eslicarbazepine and R-licarbazepine, respectively (table 1). A further block occurs at higher concentrations of the test agents, with an IC50 of 62.61 μM for eslicarbazepine and 883.10 μM for R-licarbazepine (figure 1, table 1). OXC, up to 30 μM, was devoid of effect on hCa_v3.2 currents. Regarding the reference compounds, 1 mM valproic acid blocked hCa_v3.2 calcium peak currents by 66.15 ± 2.05 % and mibefradil dose dependently inhibited hCa_v3.2 calcium peak currents with an IC50 of 143.7 nM. Cobalt chloride (5 mM) blocked hCa_v2.1 calcium peak currents by 5.02 ± 2.24 %. Conclusions: These results demonstrated that eslicarbazepine effectively inhibits high and low affinity Ca_v3.2 inward currents with higher affinity than R-licarbazepine or OXC. These findings may have implications for the clinical activity of ESL.