title: Nicotine decreases the activity of glutamate transporter type 3.
abstract: Nicotine, the main ingredient of tobacco, elicits seizures in animal models and cigarette smoking is regarded as a behavioral risk factor associated with epilepsy or seizures. In the hippocampus, the origin of nicotine-induced seizures, most glutamate uptake could be performed primarily by excitatory amino acid transporter type 3 (EAAT3). An association between temporal lobe epilepsy and EAAT3 downregulation has been reported. Therefore, we hypothesized that nicotine may elicit seizures through the attenuation of EAAT3 activity. We investigated chronic nicotine exposure (72 h) cause reduction of the activity of EAAT3 in a Xenopus oocyte expression system using a two-electrode voltage clamp. The roles of protein kinase C (PKC) and phosphatidylinositol 3-kinase (PI3K) were also determined. Nicotine (0.001-1 μM) resulted in a time- and dose-dependent decrease in EAAT3 activity with maximal inhibition at nicotine concentrations of 0.03 μM or higher and at an exposure time of 72 h. Vmax on the glutamate response was significantly reduced in the nicotine group (0.03 μM for 72 h), but the Km value of EAAT3 for glutamate was not altered. When nicotine-exposed oocytes (0.03 μM for 72 h) were pretreated with phorbol-12-myristate-13-acetate (PMA, a PKC activator), the nicotine-induced reduction in EAAT3 activity was abolished. PKC inhibitors (staurosporine, chelerythrine, and calphostin C) significantly reduced basal EAAT3 activity, but there were no significant differences among the PKC inhibitors, nicotine, and PKC inhibitors+nicotine groups. Similar response patterns were observed among PI3K inhibitors (wortmannin and LY294002), nicotine, and PI3K inhibitors+nicotine. In conclusion, this study suggests that nicotine decreases EAAT3 activity, and that this inhibition seems to be dependent on PKC and PI3K. Our results may provide an additional mechanism for nicotine-induced seizure.
authors.affiliation: Department of Anesthesiology and Pain Medicine, Cheil General Hospital, Kwandong University, Mukjung-dong, Jun-gu, Seoul, South Korea.
authors.forename: Hea-Jo
authors.initials: HJ
authors.lastname: Yoon
authors.affiliation: Department of Anesthesiology and Pain Medicine, Seoul National University Hospital, Yongon-dong, Chongno-gu, Seoul, South Korea.
authors.forename: Young-Jin
authors.initials: YJ
authors.lastname: Lim
authors.affiliation: Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA, USA.
authors.forename: Zhiyi
authors.initials: Z
authors.lastname: Zuo
authors.affiliation: Department of Anesthesiology and Pain Medicine, Guro Hospital, Korea University, Guro-dong, Guru-gu, Seoul, South Korea.
authors.forename: Wonseok
authors.initials: W
authors.lastname: Hur
authors.affiliation: Department of Anesthesiology and Pain Medicine, Seoul National University Bundang Hospital, Seongnam-si, Gyeonggi-do, South Korea. Electronic address: shdo@snu.ac.kr.
authors.forename: Sang-Hwan
authors.initials: SH
authors.lastname: Do
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D020536:Enzyme Activators / Q000494:pharmacology; D050580:Excitatory Amino Acid Transporter 3 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism*; D008564:Membrane Potentials; D009538:Nicotine / Q000633:toxicity*; D018722:Nicotinic Agonists / Q000633:toxicity*; D009865:Oocytes; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D012640:Seizures / Q000139:chemically induced / Q000378:metabolism; D013997:Time Factors; D014982:Xenopus laevis
chemical_list: D020536:Enzyme Activators; D050580:Excitatory Amino Acid Transporter 3; D018722:Nicotinic Agonists; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; C493398:Slc1a1 protein, rat; D018698:Glutamic Acid; D009538:Nicotine; D058539:Phosphatidylinositol 3-Kinase; D011493:Protein Kinase C
keywords: Excitatory amino acid transporter 3; Glutamate plasma membrane transport protein; Nicotine; Phosphatidylinositol 3-kinase; Protein kinase C; Xenopus laevis