Immune co-labeling of P-gp/caveolin-1 in capillary endothelial cells. (×40 ×2 zoom). (a, e) Nuclear staining. (b, f) P-gp labeling appears concentrated in the luminal compartment of the endothelial cells. (c, g) Caveolin-1 stains the entire endothelial cytoplasm with fine puncta in the luminal compartment and larger, intensely immunoreactive puncta in the abluminal compartment. (d, h) The merged images show P-gp and caveolin-1 co-expression (yellowish fluorescence). the two proteins co-localize either in the luminal endothelial compartment (d, arrow) or at the border of the luminal/abluminal compartments (h, arrow).