Effective Perturbations by Phenobarbital on I Na , I K(erg) , I K(M) and I K(DR) during Pulse Train Stimulation in Neuroblastoma Neuro-2a Cells.

Phenobarbital (PHB, Luminal Sodium ® ) is a medication of the barbiturate and has long been recognized to be an anticonvulsant and a hypnotic because it can facilitate synaptic inhibition in the central nervous system through acting on the γ-aminobutyric acid (GABA) type A (GABA A ) receptors. However, to what extent PHB could directly perturb the magnitude and gating of different plasmalemmal ionic currents is not thoroughly explored. In neuroblastoma Neuro-2a cells, we found that PHB effectively suppressed the magnitude of voltage-gated Na + current ( I Na ) in a concentration-dependent fashion, with an effective IC 50 value of 83 µM. The cumulative inhibition of I Na , evoked by pulse train stimulation, was enhanced by PHB. However, tefluthrin, an activator of I Na , could attenuate PHB-induced reduction in the decaying time constant of I Na inhibition evoked by pulse train stimuli. In addition, the erg ( ether-à-go-go -related gene)-mediated K + current ( I K(erg) ) was also blocked by PHB. The PHB-mediated inhibition on I K(erg) could not be overcome by flumazenil (GABA antagonist) or chlorotoxin (chloride channel blocker). The PHB reduced the recovery of I K(erg) by a two-step voltage protocol with a geometrics-based progression, but it increased the decaying rate of I K(erg) , evoked by the envelope-of-tail method. About the M-type K + currents ( I K(M) ), PHB caused a reduction of its amplitude, which could not be counteracted by flumazenil or chlorotoxin, and PHB could enhance its cumulative inhibition during pulse train stimulation. Moreover, the magnitude of delayed-rectifier K + current ( I K(DR) ) was inhibited by PHB, while the cumulative inhibition of I K(DR) during 10 s of repetitive stimulation was enhanced. Multiple ionic currents during pulse train stimulation were subject to PHB, and neither GABA antagonist nor chloride channel blocker could counteract these PHB-induced reductions. It suggests that these actions might conceivably participate in different functional activities of excitable cells and be independent of GABA A receptors.