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Doxepin and imipramine but not fluoxetine reduce the activity of the rat glutamate transporter EAAT3 expressed in Xenopus oocytes.

Park HJ, Baik HJ, Kim DY, Lee GY, Woo JH, Zuo Z, Chung RK - BMC Anesthesiol (2015)

Bottom Line: Doxepin at 0.063-1.58 μM significantly decreased EAAT3 activity.However, 0.79 μM doxepin did not abolish the enhancement of EAAT3 activity by PMA.PKC may be involved in the effects of doxepin on EAAT3, but is not involved in the effects of imipramine at the concentrations studied.

View Article: PubMed Central - PubMed

Affiliation: Dasom anesthesia and analgesia practice association, Seoul, Republic of Korea. ithiel3@hanmail.net.

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.

No MeSH data available.


Related in: MedlinePlus

Dose–response of fluoxetine on EAAT3 responses to L-glutamate (30 μM). Data are means ± S.E.M. (n = 17–26 for each data point). *p < 0.05 vs. control
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Fig3: Dose–response of fluoxetine on EAAT3 responses to L-glutamate (30 μM). Data are means ± S.E.M. (n = 17–26 for each data point). *p < 0.05 vs. control

Mentions: Non-injected oocytes were unresponsive to L-glutamate (data not shown), but oocytes injected with EAAT3 mRNA showed inward currents after L-glutamate was applied (Figs. 1, 2 and 3). This current was shown to be mediated via EAAT3 in previous studies [21, 22]. In the vehicle control experiment, 0.03 % (v/v) methanol (the highest concentration in Tyrode’s solution containing imipramine) had no effect on the current response to glutamate (0.96 ± 0.34-fold) compared with the control (1.00 ± 0.35-fold) (n = 10, p > 0.05).Fig. 1


Doxepin and imipramine but not fluoxetine reduce the activity of the rat glutamate transporter EAAT3 expressed in Xenopus oocytes.

Park HJ, Baik HJ, Kim DY, Lee GY, Woo JH, Zuo Z, Chung RK - BMC Anesthesiol (2015)

Dose–response of fluoxetine on EAAT3 responses to L-glutamate (30 μM). Data are means ± S.E.M. (n = 17–26 for each data point). *p < 0.05 vs. control
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4528682&req=5

Fig3: Dose–response of fluoxetine on EAAT3 responses to L-glutamate (30 μM). Data are means ± S.E.M. (n = 17–26 for each data point). *p < 0.05 vs. control
Mentions: Non-injected oocytes were unresponsive to L-glutamate (data not shown), but oocytes injected with EAAT3 mRNA showed inward currents after L-glutamate was applied (Figs. 1, 2 and 3). This current was shown to be mediated via EAAT3 in previous studies [21, 22]. In the vehicle control experiment, 0.03 % (v/v) methanol (the highest concentration in Tyrode’s solution containing imipramine) had no effect on the current response to glutamate (0.96 ± 0.34-fold) compared with the control (1.00 ± 0.35-fold) (n = 10, p > 0.05).Fig. 1

Bottom Line: Doxepin at 0.063-1.58 μM significantly decreased EAAT3 activity.However, 0.79 μM doxepin did not abolish the enhancement of EAAT3 activity by PMA.PKC may be involved in the effects of doxepin on EAAT3, but is not involved in the effects of imipramine at the concentrations studied.

View Article: PubMed Central - PubMed

Affiliation: Dasom anesthesia and analgesia practice association, Seoul, Republic of Korea. ithiel3@hanmail.net.

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.

No MeSH data available.


Related in: MedlinePlus