Nicotine decreases the activity of glutamate transporter type 3

• Published in: Toxicology letters Vol. 225; no. 1; pp. 147 - 152
• Main Authors: Yoon, Hea-Jo, Lim, Young-Jin, Zuo, Zhiyi, Hur, Wonseok, Do, Sang-Hwan
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ireland Ltd 10.02.2014
• Subjects: Animals; Dose-Response Relationship, Drug; Enzyme Activation; Enzyme Activators - pharmacology; Excitatory amino acid transporter 3; Excitatory Amino Acid Transporter 3 - antagonists & inhibitors; Excitatory Amino Acid Transporter 3 - genetics; Excitatory Amino Acid Transporter 3 - metabolism; Female; Glutamate plasma membrane transport protein; Glutamic Acid - metabolism; Membrane Potentials; Nicotine; Nicotine - toxicity; Nicotinic Agonists - toxicity; Oocytes; Phosphatidylinositol 3-kinase; Phosphatidylinositol 3-Kinase - antagonists & inhibitors; Phosphatidylinositol 3-Kinase - metabolism; Protein kinase C; Protein Kinase C - antagonists & inhibitors; Protein Kinase C - metabolism; Protein Kinase Inhibitors - pharmacology; Rats; Seizures - chemically induced; Seizures - metabolism; Time Factors; Xenopus laevis; Glutamate plasma membrane transport protein; Protein kinase C; Phosphatidylinositol 3-kinase; Excitatory amino acid transporter 3; Xenopus laevis; Nicotine
• ISSN: 0378-4274; 1879-3169
• DOI: 10.1016/j.toxlet.2013.12.002

•Nicotine (0.001–1μM) resulted in a time- and dose-dependent decrease in EAAT3 activity in a Xenopus oocyte expression system.•Nicotine decreases EAAT3 activity, but seems to be dependent on PKC and PI3K.•Our results may provide an additional mechanism for nicotine-induced seizure. 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 (72h) 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 (0.001–1μM) resulted in a time- and dose-dependent decrease in EAAT3 activity with maximal inhibition at nicotine concentrations of 0.03μM or higher and at an exposure time of 72h. Vmax on the glutamate response was significantly reduced in the nicotine group (0.03μM for 72h), but the Km value of EAAT3 for glutamate was not altered. When nicotine-exposed oocytes (0.03μM for 72h) 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.