Antiepileptic drugs--calcium current interaction in cultured human neuroblastoma cells

The voltage-dependent calcium channel current (ICa) in the neuroblastoma cell line of human origin (NB-I) was studied by the whole-cell clamp recording. Three types of ICa were identified in NB-I cells. Our electrophysiological and pharmacological findings have suggested that these three types of ICa are consistent with the T-, N- and L-type ICa, respectively. Phenytoin (PHT) inhibited T-type ICa by 13.0% at a concentration of 5 microM, and L-type ICa by 6.3% at a concentration of 100 microM. At a concentration of 100 microM, carbamazepine (CBZ) inhibited T- and L-type ICa by 6.0% and 5.9%, respectively. At a concentration of 50 microM, sodium valproate (VPA) blocked T- and L-type ICa by 6.1% and 47.5%, respectively. At a concentration of 50 microM, zomisamide (ZNS) inhibited T- and L-type ICa by 38.3% and 41.9%, respectively. Na+ channel blockade has been reported to be responsible for the clinical efficacy of PHT or CBZ. Inhibition of T-type ICa by PHT may enhance the efficacy of its anticonvulsant action. CBZ had little effect on ICa. The anticonvulsant activity may be related to the blockade of T-type ICa in the case of VPA and ZNS.