Publication Details (including relevant citation information):
Wright, Rebecca A., Arnold, M. Brian, Wheeler, William J., Ornstein, Paul L., Schoepp, Darryle D. Naunyn-Schmiedeberg's Archives of Pharmacology 2000 362 (6) 546-554
Abstract: LY341495 is a highly potent and selective antagonist for group II mGlu receptors (mGlu2 and mGlu3). High affinity binding of (3H)LY341495 to recombinant human group II mGlu receptors (mGlu2 and mGlu3), and in rat brain homogenates (Kd apprx1 nM), has been previously described. Although LY341495 is a very selective nM-potent antagonist for group II mGlu receptors, it is also a relatively potent antagonist for group III mGlu receptors at high nanomolar to low micromolar concentrations. In this study we examined and characterized the binding of (3H)LY341495 to membranes of cells expressing recombinant human group III mGlu receptors. Using up to 100 nM of (3H)LY341495, the level of specific binding in human mGlu4a receptor-expressing cell membranes was not appreciable and binding to this site was not examined further. In contrast, we demonstrated sufficient specific binding of (3H)LY341495 to human mGlu6, mGlu7a and mGlu8a receptor-expressing cell membranes to allow for further characterizations. (3H)LY341495 binding was saturable and rapidly reversible. (3H)LY341495 bound to a single site in each cell line, with Kd and Bmax values of 31.6+-6.8 nM and 3.3+-0.7 pmol/mg protein (mGlu6), 72.7+-22.0 nM and 3.7+-0.4 pmol/mg protein (mGlu7a), and 14.0+-1.1 nM and 3.0+-0.2 pmol/mg protein (mGlu8a). (3H)LY341495 binding to mGlu6, 7a and 8a was displaceable by compounds which interact functionally with group III mGlu receptors. For example, L-AP4 displaced (3H)LY341495 with Ki values of 6.8+-3.1 muM (mGlu6), 211+-43 muM (mGlu7a) and 1.6+-0.3 muM (mGlu8a). With L-glutamate, we obtained Ki values of 12.3+-3.5, 869+-154 and 4.5+-0.83 muM, for mGlu6, mGlu7a and mGlu8a, respectively. Ki values for unlabelled LY341495 were 0.058+-0.008, 0.22+-0.05 and 0.029+-0.008 muM, respectively. These studies demonstrated that (3H)LY341495 is a useful radioligand for studying the pharmacology and expression of recombinant mGlu6, 7a and 8a receptors in cell lines.