Effects of volatile anesthetics on glutamate transporter, excitatory amino acid transporter type 3: the role of protein kinase C.
BACKGROUND
Glutamate transporters play an important role in maintaining extracellular glutamate homeostasis. The authors studied the effects of volatile anesthetics on one type of glutamate transporters, excitatory amino acid transporter type 3 (EAAT3), and the role of protein kinase C in mediating these effects.


METHODS
Excitatory amino acid transporter type 3 was expressed in Xenopus oocytes by injection of EAAT3 mRNA. Using two-electrode voltage clamp, membrane currents were recorded before, during, and after application of L-glutamate. Responses were quantified by integrating the current trace and are reported as microcoulombs. Data are mean +/- SEM.


RESULTS
L-Glutamate-induced responses were increased gradually with the increased concentrations of isoflurane, a volatile anesthetic. At 0.52 and 0.70 mm isoflurane, the inward current was significantly increased compared with control. Isoflurane (0.70 mm) significantly increased Vmax (maximum velocity) (3.6 +/- 0.4 to 5.1 +/- 0.4 microC; P < 0.05) but not Km (Michoelis-Menten Constant) (55.4 +/- 17.0 vs. 61.7 +/- 13.6 microm; P > 0.05) of EAAT3 for glutamate compared with control. Treatment of the oocytes with phorbol-12-myrisate-13-acetate, a protein kinase C activator, caused a significant increase in transporter current (1.7 +/- 0.2 to 2.5 +/- 0.2 microC; P < 0.05). Responses in the presence of the combination of phorbol-12-myrisate-13-acetate and volatile anesthetics (isoflurane, halothane, or sevoflurane) were not greater than those when volatile anesthetic was present alone. Oocytes pretreated with any of the three protein kinase C inhibitors alone (chelerythrine, staurosporine, or calphostin C) did not affect basal transporter current. Although chelerythrine did not change the anesthetic effects on the activity of EAAT3, staurosporine or calphostin C abolished the anesthetic-induced increase of EAAT3 activity.


CONCLUSIONS
These data suggest that volatile anesthetics enhance EAAT3 activity and that protein kinase C is involved in mediating these anesthetic effects.
Do
Sang-Hwan
SH
Department of Anesthesiology, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908, USA.
Kamatchi
Ganesan L
GL
Washington
Jacqueline M
JM
Zuo
Zhiyi
Z
D027322:Amino Acid Transport System X-AG; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D002352:Carrier Proteins / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D005260:Female; D050491:Glutamate Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000378:metabolism; D011493:Protein Kinase C / Q000502:physiology; D027981:Symporters; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014982:Xenopus laevis
D027322:Amino Acid Transport System X-AG; D018685:Anesthetics, Inhalation; D002352:Carrier Proteins; D050491:Glutamate Plasma Membrane Transport Proteins; D027981:Symporters; D018698:Glutamic Acid; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate