The γ‐aminobutyric acid receptor B, but not the metabotropic glutamate receptor type‐1, associates with lipid rafts in the rat cerebellum

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Abstract
Recent evidence suggests that specialized microdomains, called lipid rafts, exist within plasma membranes. These domains are enriched in cholesterol and sphingolipids and are resistant to non-ionic detergent-extraction at 4°C. They contain specific populations of membrane proteins, and can change their size and composition in response to cellular signals, resulting in activation of signalling cascades. Here, we demonstrate that both the metabotropic γ-aminobutyric acid receptor B (GABAB receptor) and the metabotropic glutamate receptor-1 from rat cerebellum are insoluble in the non-ionic detergent Triton X-100. However, only the GABAB receptor associates with raft fractions isolated from rat brain by sucrose gradient centrifugation. Moreover, increasing the stringency of isolation by decreasing the protein : detergent ratio caused an enrichment of the GABAB receptor in raft fractions. In contrast, depletion of cholesterol from cerebellar membranes by either saponin or methyl-β-cyclodextrin treatment, which solubilize known raft markers, also increased the solubility of the GABAB receptor. These properties are all consistent with an association of the GABAB receptor with lipid raft microdomains.