Back -phosphorylation of GluR1 in the retina of the rdta mice and their littermate controls. (A) Ten micrograms of SPM protein from the retinae of the rdta mice and their littermate controls were back-phosphorylated by endogenous CaMKII in the presence of Ca2+/CaM. The samples were then electrophoresed by SDS-PAGE and subsequently transferred to nitrocellular membrane. The phosphorylated bands were visualized by autoradiography. The in vitro phosphorylation was higher in the littermate controls than in the rdta mice. (B) The same blots were then incubated with anti-GluR1 antibody and visualized by alkaline phosphatase conjugated secondary antibody and NBI/BICP substrate. The molecular weight of GluR1 is indicated. The density for GluR1 was elevated in the rdta mice relative to the littermate controls. (C) GluR1s were immunoprecipitated after the back-phosphorylation and subjected to SDS-PAGE. The gel was dried and the image was visualized by autoradiography. These data indicate that the phosphorylation of GluR1 is increased in vivo in the retina of the rdta mice relative to their littermate controls.