Striped structures on the cytoplasmic surface membranes of the endothelial vesicles of the rat aorta revealed by quick-freeze, deep-etching replicas.

The cytoplasmic surface of plasmalemmal vesicles in aortic endothelial cells was examined in quick-freeze, deep-etching replicas. In addition to the clathrin-coated vesicles, striped patterns were observed over the cytoplasmic surface membranes of small vesicles (60-80 nm in diameter) in the unfixed specimens. These patterns were more clearly visible in saponin-extracted specimens; the stripes were composed of several ridges or strands of 6-10 nm in width, and some were crossed. These were distinct from the characteristic pentagons or hexagons of the clathrin-coated vesicles. This striped structure was enhanced by treatment with myosin subfragment-1 or phalloidin, thereby indicating a possible relation to actin filaments. Patchy plaques with similar striped patterns appeared on the cytoplasmic surface of the plasmalemma proper and also on the cytoplasmic vacuole membranes together with clathrin. These striped structures may be involved in the formation and transport of so-called "uncoated" vesicles.