Effects of clonidine on the activity of the rat glutamate transporter EAAT3 expressed in Xenopus oocytes

Background: Clonidine has been shown to be a potent neuroprotectant by acting at α₂ receptors on glutamatergicneurons to inhibit the release of glutamate. The aim of this study is to investigate the effects of clonidine on theactivity of EAAT3 that can regulate extracellular glutamate.Methods: EAAT3 was expressed in the Xenopus oocytes. Using a two-electrode voltage clamp, membrane currentswere recorded after application of 30 μM L-glutamate both in the presence and absence of various concentrationsof clonidine. To determine the effects of clonidine on the K_m and Vmax of EAAT3 and the reversibility of clonidineeffects, membrane currents were recorded after the application of various concentrations of L-glutamate both in thepresence and absence of 1.50 × 10^-7 M clonidine. Results: Clonidine reduced the EAAT3 responses to L-glutamate in a concentration-dependent manner. Thisinhibition was statistically significant at higher concentrations than at the clinically relevant range. Clonidine at 1.50× 10^-7 M reduced the Vmax, but did not affect the K_m of EAAT3 for L-glutamate.Conclusions: These results suggest that the direct inhibition of EAAT3 activity is not related to the sedation effectof clonidine and that the clonidine-induced reduction of EAAT3 activity provides additional data for the possibleinvolvement of glutamatergic hyperactivity in the proconvulsant effect of clonidine.