title: Doxepin and imipramine but not fluoxetine reduce the activity of the rat glutamate transporter EAAT3 expressed in Xenopus oocytes.
abstract: BACKGROUND
  Many researchers have suggested that the glutamatergic system may be involved in the effects of antidepressant therapies. We investigated the effects of doxepin, imipramine, and fluoxetine on the excitatory amino acid transporter type 3 (EAAT3).
  
  
  METHODS
  EAAT3 was expressed in Xenopus oocytes by injection of EAAT3 mRNA. Membrane currents were recorded after application of L-glutamate (30 μM) in the presence or absence of various concentrations of doxepin, imipramine, and fluoxetine. To study the effects of protein kinase C (PKC) activation on EAAT3 activity, oocytes were pre-incubated with phorbol 12-myristate-13-acetate (PMA) before application of imipramine and doxepin.
  
  
  RESULTS
  Doxepin at 0.063-1.58 μM significantly decreased EAAT3 activity. Imipramine reduced EAAT3 activity in a concentration-dependent manner at 0.16-0.95 μM. However, fluoxetine did not affect EAAT3 activity, and PMA increased EAAT3 activity. At 0.32 μM, imipramine caused an equivalent decrease in EAAT3 activity in the presence or absence of PMA. However, 0.79 μM doxepin did not abolish the enhancement of EAAT3 activity by PMA.
  
  
  CONCLUSIONS
  We showed that doxepin and imipramine, but not fluoxetine, inhibited EAAT3 activity at clinically relevant concentrations. This reveals a novel mechanism of action for doxepin and imipramine; that they increase glutamatergic neurotransmission. PKC may be involved in the effects of doxepin on EAAT3, but is not involved in the effects of imipramine at the concentrations studied.
authors.affiliation: Dasom anesthesia and analgesia practice association, Seoul, Republic of Korea. ithiel3@hanmail.net.
authors.forename: Hye Jin
authors.initials: HJ
authors.lastname: Park
authors.affiliation: Department of anesthesiology and pain medicine, School of Medicine, Ewha Womans University, Seoul, Republic of Korea. baikhj@ewha.ac.kr.
authors.forename: Hee Jung
authors.initials: HJ
authors.lastname: Baik
authors.affiliation: Department of anesthesiology and pain medicine, School of Medicine, Ewha Womans University, Seoul, Republic of Korea. kdyeon@ewha.ac.kr.
authors.forename: Dong Yeon
authors.initials: DY
authors.lastname: Kim
authors.affiliation: Department of anesthesiology and pain medicine, School of Medicine, Ewha Womans University, Seoul, Republic of Korea. lgyanes@ewha.ac.kr.
authors.forename: Guie Yong
authors.initials: GY
authors.lastname: Lee
authors.affiliation: Department of anesthesiology and pain medicine, School of Medicine, Ewha Womans University, Seoul, Republic of Korea. jheewoo@ewha.ac.kr.
authors.forename: Jae Hee
authors.initials: JH
authors.lastname: Woo
authors.affiliation: Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA, USA. zz3c@virginia.edu.
authors.forename: Zhiyi
authors.initials: Z
authors.lastname: Zuo
authors.affiliation: Department of anesthesiology and pain medicine, School of Medicine, Ewha Womans University, Seoul, Republic of Korea. rkchung@ewha.ac.kr.
authors.forename: Rack Kyung
authors.initials: RK
authors.lastname: Chung
mesh_terms: D000818:Animals; D000928:Antidepressive Agents / Q000008:administration & dosage / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004316:Doxepin / Q000008:administration & dosage / Q000494:pharmacology*; D050580:Excitatory Amino Acid Transporter 3 / Q000037:antagonists & inhibitors*; D005260:Female; D005473:Fluoxetine / Q000008:administration & dosage / Q000494:pharmacology*; D018698:Glutamic Acid / Q000378:metabolism; D007099:Imipramine / Q000008:administration & dosage / Q000494:pharmacology*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014982:Xenopus laevis
chemical_list: D000928:Antidepressive Agents; D050580:Excitatory Amino Acid Transporter 3; D012333:RNA, Messenger; D005473:Fluoxetine; D004316:Doxepin; D018698:Glutamic Acid; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D007099:Imipramine