These assays were done exactly as previously (Ghosh et al., 2010 (link); Garcia-Marcos et al., 2011a (link)), using a confocal Leica SPE microscope. To visualize all populations of receptors in cells, images were acquired as Z-stacks and maximally projected. Briefly, cells were fixed at room temperature with 3% paraformaldehyde for 20–25 min, permeabilized (0.2% Triton X-100) for 45 min, and incubated for 1 h each with primary and then secondary antibodies as described previously (Ghosh et al., 2008 (link)). Antibody dilutions were as follows: mAb green fluorescent protein, 1:500; secondary goat anti-rabbit (594) and goat anti-mouse (488) Alexa-conjugated antibodies, 1:500; and 4′,6-diamidino-2-phenylindole (DAPI), 1:2000 (Molecular Probes). Samples were examined with a Leica SPE confocal microscope (Leica) using a 63× objective, and collected images were processed using ImageJ software (National Institutes of Health, Bethesda, MD) and assembled for presentation using Photoshop and Illustrator software (Adobe).