title: Inhibitory effects of the antiepileptic drug ethosuximide on G protein-activated inwardly rectifying K+ channels.
abstract: Antiepileptic drugs protect against seizures by modulating neuronal excitability. Ethosuximide is selectively used for the treatment of absence epilepsy, and has also been shown to have the potential for treating several other neuropsychiatric disorders in addition to several antiepileptic drugs. Although ethosuximide inhibits T-type Ca(2+), noninactivating Na(+), and Ca(2+)-activated K(+) channels, the molecular mechanisms underlying the effects of ethosuximide have not yet been sufficiently clarified. G protein-activated inwardly rectifying K(+) channels (GIRK, or Kir3) play an important role in regulating neuronal excitability, heart rate and platelet aggregation. In the present study, the effects of various antiepileptic drugs on GIRK channels were examined first by using the Xenopus oocyte expression assay. Ethosuximide at clinically relevant concentrations inhibited GIRK channels expressed in Xenopus oocytes. The inhibition was concentration-dependent, but voltage-independent, and time-independent during each voltage pulse. However, the other antiepileptic drugs tested: phenytoin, valproic acid, carbamazepine, phenobarbital, gabapentin, topiramate and zonisamide, had no significant effects on GIRK channels even at toxic concentrations. In contrast, Kir1.1 and Kir2.1 channels were insensitive to all of the drugs tested. Ethosuximide also attenuated ethanol-induced GIRK currents. These inhibitory effects of ethosuximide were not observed when ethosuximide was applied intracellularly. In granule cells of cerebellar slices, ethosuximide inhibited GTPgammaS-activated GIRK currents. Moreover, ADP- and epinephrine-induced platelet aggregation was inhibited by ethosuximide, but not by charybdotoxin, a platelet Ca(2+)-activated K(+) channel blocker. These results suggest that the inhibitory effects of ethosuximide on GIRK channels may affect some of brain, heart and platelet functions.
authors.affiliation: Department of Molecular Neuropathology, Brain Research Institute, Niigata University, 1-757 Asahimachi, Chuo-ku, Niigata, Niigata 951-8585, Japan. torukoba@bri.niigata-u.ac.jp
authors.forename: Toru
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Hirai
authors.forename: Masae
authors.initials: M
authors.lastname: Iino
authors.forename: Ichiro
authors.initials: I
authors.lastname: Fuse
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Mitsumura
authors.forename: Kazuo
authors.initials: K
authors.lastname: Washiyama
authors.forename: Shinya
authors.initials: S
authors.lastname: Kasai
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Ikeda
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D000927:Anticonvulsants / Q000494:pharmacology*; D017609:Barium Compounds / Q000494:pharmacology; D002492:Central Nervous System Depressants / Q000494:pharmacology; D002531:Cerebellum / Q000166:cytology; D002712:Chlorides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D000431:Ethanol / Q000494:pharmacology; D005013:Ethosuximide / Q000494:pharmacology*; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels / Q000235:genetics / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects* / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008845:Microinjections / Q000379:methods; D009433:Neural Inhibition / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D014981:Xenopus
chemical_list: D000927:Anticonvulsants; D017609:Barium Compounds; D002492:Central Nervous System Depressants; D002712:Chlorides; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; C024986:barium chloride; D000431:Ethanol; D005013:Ethosuximide; D000244:Adenosine Diphosphate