Fig. 4.

Direct activation of Δ5Δ by the positive allosteric regulator DFB. (A) Effect of increasing doses of DFB on Δ5Δ. DFB dose-dependently activates the truncated receptor Δ5Δ. The curve has been normalized such that the basal response is zero and the maximum is 100%. (Inset) IP formation (% above the basal) was induced by DFB only in cells expressing Δ5Δ and not in cells expressing mGlu₅. (B) Direct stimulation of Δ5 and Δ5Δ by 100 μM DFB as revealed by intracellular Ca²⁺ measurement with Fluo-4. (C) Activity of mGlu₅ (squares) and Δ5Δ (circles) as a function of their membrane expression. Cells were transfected with increasing amounts of cDNA coding for these receptors, and surface expression of mGlu₅ and Δ5Δ was measured by ELISA on intact cells. Basal (open symbols) and glutamate-(1 mM) or DFB-(1 mM) (filled symbols) induced IP formation was measured in parallel.