Flunarizine selectively blocks transient calcium channel currents in N1E-115 cells

The sensitivities of two types of voltage-dependent calcium channel currents in N1E-115 neuroblastoma cells to various agents were studied using the whole cell version of the patch clamp technique. Cells cultured in normal media expressed predominantly transient (T) currents whereas cells cultured in media with dimethylsulfoxide for 1 month expressed predominantly long-lasting (L) currents. Furthermore, by selecting cells with one or two short neurites it was possible to obtain cells which expressed only L channels. The dihydropyridine agonist, Bay K-8644 (5 microM), increased the amplitude of L channel currents by a factor of nearly two, whereas T channel currents were unaffected. Nifedipine (0.1 mM) significantly inhibited L channel currents, whereas T channel currents were insensitive to this treatment. Flunarizine, a diphenylpiperazine, had no effect on L channel currents but selectively inhibited T channel currents in a dose-dependent manner, with a significant effect at a concentration of 1 microM. However, flunarizine did not change the I-V relationships of T channel currents. Furthermore, the voltage dependence of T channel inactivation was shifted toward more negative potential by flunarizine. The present study provides direct evidence of the selective inhibition of T channel currents by flunarizine in N1E-115 neuroblastoma cells.