Characterization of [ 3H]-LY354740 binding to rat mGlu2 and mGlu3 receptors expressed in CHO cells using Semliki Forest virus vectors

The binding properties of [ 3H]-LY354740 were characterized on rat metabotropic glutamate receptors mGlu2 and mGlu3 expressed in Chinese hamster ovary (CHO) cells using Semliki Forest virus vectors. The saturation isotherm gave K D values of 20±5 and 53±8 nM and B max values of 474±161 and 667±89 fmol/mg protein for mGlu2 and mGlu3 receptors, respectively. NMDA, CaCl 2, DHPG and kainate were inactive up to 1 mM, whereas LY341495, DCG IV and ibotenate inhibited [ 3H]-LY354740 binding with similar potencies on both receptors. l-CCG I, l-AP4, l-AP5, LY354740 and 1 S,3 R-ACPD were 2- to 4-fold more potent inhibitors of [ 3H]-LY354740 binding to mGlu2 than mGlu3 receptors. However, MPPG and l-AP3 had a 6-fold and DTT a 28-fold preference for mGlu2 over mGlu3. ZnCl 2, at 10 mM, inhibited more than 70% of [ 3H]-LY354740 binding to mGlu2 receptors. At the same concentration it did not affect significantly [ 3H]-LY354740 binding to mGlu3 receptors. On the contrary, glutamate, quisqualate, EGLU and NAAG showed a 3-, 5-, 7- and 12-fold preference for mGlu3 over mGlu2. Finally, GTPγS, which partially inhibited the binding on mGlu2 receptors, was inactive to inhibit [ 3H]-LY354740 binding on mGlu3 receptors.