Kainate Receptors in Xenopus Central Nervous System: Solubilisation with n-Octyl-?-d-Glucopyranoside

Abstract

[3H]Kainate binding to membrane homogenates and detergent extracts prepared fromXenopus central nervous system was evaluated in 50 mM Tris-citrate buffer, pH 7.0. In membrane fragment preparations, [3H]kainate bound with a DD of 54.4 nM to a large number of sites (Bmax = 27.8 pmol/mg of protein). Up to 80% of the total number of membrane-bound binding sites were solubilised using the nonionic detergent n-octyl-.beta.-D-glucopyranoside. Values for the KD of [3H]kainate for solubilised binding sites were 46.0 nM and 53.6 nM derived from equilibrium and kinetic binding experiments, respectively. Competitive binding studies revealed that a variety of ligands had similar Ki values in both membranes and solubilised extracts, with domoate and kainate being the most potent inhibitors of [3H]kainate binding. The dissociation rate of [3H]kainate from solubilised binding site was 0.022 min-1. The binding component migrated in sucrose density gradients in a single 8.6S peak. These results demonstrate that the kainate receptor in Xenopus central nervous system, although similar to the [3H]kainate binding site from goldfish brain, differs in a number of important respects. In particular the slower dissociation rate and higher affinity of [3H]kainate suggest that Xenopus provides the most convenient model system yet investigated for biochemical analysis of kainate receptors.