Figure 7.

Residues 871-877 function as a forward trafficking determinant for GFP-GluR6 receptors in neurons. A, Representative fluorescent images from cultured hippocampal neurons transfected with GFP-GluR6, R6-850stop, R6(871-873A), R6(873-877A), R6del873-877, and R6(871-877A) receptors. Nonpermeabilized neurons were incubated with anti-GFP antibody before fixation to label surface receptors (red). As observed with the COS-7 transfections, GFP-GluR6 was expressed at high levels on the plasma membrane. R6(873-877A) receptors also trafficked efficiently to the surface in neurons, in contrast to their expression in COS-7 cells. R6-850stop, R6(871-873A), R6(871-877A), and R6del873-877 receptors were expressed only at very low levels on the neuronal surface. B, Relative surface expression of the receptors was determined by analyzing red to green fluorescence ratios and normalizing to the GFP-GluR6 ratio as detailed in Materials and Methods. GFP-GluR6 receptors were expressed efficiently on the plasma membrane by neurons, and R6(873-877A) receptors were present at only slightly lower levels than GFP-GluR6. R6-850stop and R6(871-873A) receptors had relative surface expression ∼20% that of GFP-GluR6 receptors, whereas R6(871-877A) and R6del873-877 receptors exhibited very low surface expression (<10% of that of GFP-GluR6 receptors; 8-11 neurons analyzed for each construct).