Effects of Volatile Anesthetics on Glutamate Transporter, Excitatory Amino Acid Transporter Type 3: The Role of Protein Kinase C

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BackgroundGlutamate 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.MethodsExcitatory 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.Resultsl-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 μC;P < 0.05) but not Km (Michoelis-Menten Constant) (55.4 ± 17.0 vs. 61.7 ± 13.6 μm;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 μC;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.ConclusionsThese data suggest that volatile anesthetics enhance EAAT3 activity and that protein kinase C is involved in mediating these anesthetic effects.

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