FIGURE 2.

Screening for a peptide sequence present in the C-terminal domain of GABA_B2 that blocks glutamate-induced downregulation of GABA_B receptors. (A) Sequence of the C-terminal domain of GABA_B2 with the coiled-coil domain indicated in gray and the overlapping peptides R2C1, R2C2 and R2C3 used in (B) shown below. (B,B’) Peptides R2C1 and R2C2 increased expression of GABA_B receptors and restored glutamate-induced downregulated receptor cell surface levels. Cultures were stressed for 60 min with glutamate (50 μM) and immediately thereafter treated for 16 h with the peptides indicated in (A). Neurons were then tested for cell surface expression of endogenous GABA_B receptors using antibodies directed against the N-terminus of GABA_B2. (B) Representative images of GABA_B2 cell surface staining (scale bar: 5 μm). (B’) Quantification of the fluorescence intensities. The data were normalized to cultures not treated with glutamate and peptides and represent the mean ± SD of 45 neurons derived from three independent experiments. Two-way ANOVA followed by Tukey’s multiple comparison test (ns, p > 0.05, ****p < 0.0001.