Amitriptyline inhibits the activity of the rat glutamate transporter EAAT3 expressed in Xenopus oocytes.
OBJECTIVE
Evidence suggests that glutamatergic systems may be involved in the pathophysiology of major depression and the mechanism of action of antidepressants. We have investigated the effects of amitriptyline, a tricyclic antidepressant, on the activity of the excitatory amino acid transporter type 3 (EAAT3), a protein that can regulate extracellular glutamate concentrations in the brain.


METHODS
EAAT3 was expressed in Xenopus oocytes. Using a two-electrode voltage clamp, membrane currents were recorded after application of 30 microM L-glutamate in the presence or absence of various concentrations of amitriptyline or after application of various concentrations of L-glutamate in the presence or absence of 0.64 microM amitriptyline.


RESULTS
Amitriptyline concentration-dependently reduced EAAT3 activity. This inhibition reached statistical significance at 0.38-1.27 microM amitriptyline. Amitriptyline 0.64 microM reduced the pharmacokinetic parameter Vmax, but did not affect the pharmacokinetic parameter Km, of EAAT3 for L-glutamate. The amitriptyline inhibition disappeared after a 4-min washout. Phorbol-12-myristate-13-acetate, a protein kinase C activator, increased EAAT3 activity. However, 0.64 microM amitriptyline induced a similar degree of decrease in EAAT3 activity in the presence or absence of phorbol-12-myristate-13-acetate.


CONCLUSIONS
Our results suggested that amitriptyline at clinically relevant concentrations reversibly reduced EAAT3 activity via decreasing its maximal velocity of glutamate transporting function. The effects of amitriptyline on EAAT3 activity may have represented a novel site of action for amitriptyline to increase glutamatergic neurotransmission. Protein kinase C may not have been involved in the effects of amitriptyline on EAAT3.
Baik
Hee-Jung
HJ
Department of Anesthesiology, University of Virginia, Charlottesville, VA 22908-0710, USA.
Lee
Soon-Ae
SA
Washington
Jacqueline M
JM
Zuo
Zhi-yi
ZY
D000639:Amitriptyline / Q000494:pharmacology*; D000818:Animals; D000929:Antidepressive Agents, Tricyclic / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D020536:Enzyme Activators / Q000494:pharmacology; D050580:Excitatory Amino Acid Transporter 3 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D005260:Female; D018698:Glutamic Acid / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques; D011493:Protein Kinase C / Q000502:physiology; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014982:Xenopus laevis
D000929:Antidepressive Agents, Tricyclic; D020536:Enzyme Activators; D050580:Excitatory Amino Acid Transporter 3; D000639:Amitriptyline; D018698:Glutamic Acid; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate