For immunofluorescence, cells were fixed in 4% PFA in 1× PBS for 15 to 20 minutes and permeabilized for 5 minutes with 0.1% Triton X-100 in PBS. Cells were blocked for 30 minutes with 5% goat serum and then incubated with primary antibodies (CD63 1:200, ab59479, Abcam; GluN1 1:500, MAB363, Merk & Co, Kenilworth, New Jersey, United States or Calnexin 1:1000, ab22595, Abcam) at 4°C overnight. After washing, cells were incubated with 2.5 μg mL
−1Dylight 488/594-conjugated secondary antibodies (ab96931 and ab96885, respectively; both from Abcam) for 3 hours. Giemsa staining was performed using the Cytopro autostainer (ELITech, Paris, France). Brightfield and immunofluorescence microscopy was conducted using an Eclipse Ni-E microscope (Nikon, Tokyo, Japan). Hoffman and phase contrast images were taken on an Eclipse Ti microscope (Nikon).
Transmission electron microscopy was done as previously described.
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Briefly, cells were fixed with 0.2% glutaraldehyde and 2% PFA in White's saline. Sections were counterstained with uranyl acetate and examined with a Tecnai G2 Spirit Twin transmission electron microscope (FEI Company, Hillsboro, Oregon, United States).