Cell membrane features of rabbit arterial smooth muscle. A freeze-fracture study.

The cell membrane of smooth muscle cells from four large arteries of rabbits was investigated by freeze-fracture. On the surface of the smooth muscle smooth zones could be distinguished arranged in an alternate manner with zones characterised by numerous openings of surface vesicles. Vesiculate zones formed bands of variable width, generally parallel to the long axis of the cell, or irregular patches of different size. The density of vesicles within bands and patches varied from a very loose packing to a dense, quasi-hexagonal array. Comparative morphometric studies of the cell membrane replicas showed differences in the ratio vesiculate area: smooth area and also different surface vesicle frequencies expressed either as mean values or as values for vesiculate zones, in the arteries investigated. Communicating junctions (nexuses, gap junctions) characterized by a random arrangement of particles on the P-face and a more ordered, rhomboidal array of pits on the E-face were the only type of intercellular junctions found between arterial smooth muscle cells.