Glutamate-Induced Cobalt Uptake Elicited by Kainate Receptors in Taste Cells

Objectives: Glutamate-induced cobalt uptake reveals non-NMDA glutamate receptors (GluRs) in rat taste bud cells. In central nervous system, roles of amino-3-hydroxy-5-methyl-isoxazole-propionic acid (AMPA) and kainate receptors are different. AMPA receptors mediate the majority of rapid excitatory synaptic transmission and regulate in mediating synaptic plasticity. The kinetic s of pure kainate EPSCs are slower than that of pure AMPA EPSCs and integrate excitatory inputs. However, it is not known that which type of non-NMDA glutamate receptors are involved in rat taste cells. Methods: We used a cobalt staining technique for pharmacological test of various agonist or antagonist of kainate or AMPA receptors. Tongue slices containing taste buds were obtained from 45-60 days old Sprague-Dawley rats (at least 4 animals in each group). Slices were stimulated for 5 minutes at room temperature in uptake buffer containing 5mM CoCl2 plus 1mM glutamate and/or other drugs. Thin tissue sections obtained by cryocut were used for cell counting. Cobalt ions were precipitated by ammonium sulfate and were visualized by silver enhancement. Results: The cobalt uptake were elicited by glutamate, kainate, or SYM 2081 in dose dependent manner, however, were not by AMPA or fluorowillardiine. Moreover, CNQX nearly abolished cobalt staining elicited by glutamate or kainate receptor agonist, but SYM 2206 did not . Conclusion: These results suggest that glutamate-induced cobalt uptake in taste cells elicited by kainate type glutamate receptors but not AMPA type glutamate receptors. Kainate receptors in taste cells may have important roles integrating information from many taste cells. This work was supported by grant No. R05-2002-000-00395-0 from the Basic Research Program of the Korea Science & Engineering Foundation.