Fig. 1.

Surface labeling with Ruthenium Red. Synoviocytes were fixed in the presence of the nonpermeable surface marker Ruthenium Red. The electron micrographs show the presence of numerous caveolae. Single caveolae are typically seen directly at the cell surface (a), whereas caveolae clusters are most often found deeper within the cell (b, c). Both types of caveolae were extensively stained by Ruthenium Red, and unstained caveolae (marked with asterisks in a) were only rarely observed. Intermediate-size (10 nm) cytoskeletal filaments (arrows) were frequently found in close contact with the caveolae clusters (b, c). Bars 0.1 μm (a), 0.2 μm (b), 0.5 μm (c)