Electron micrographs showing the cytoplasmic densities in vascular smooth muscle cells. Upper inset. The plane of section includes only the smooth muscle cells in the vascular wall. The rectangle in the inset shows portions of three smooth muscle cells that appear at higher magnification in the large electron micrograph. The a-actinin-containing cytoplasmic densities (single arrows) usually appear as irregular masses, some of which are in contact with, and attached to, the plasma membrane. The cell in the center of the micrograph has been cut in a plane closer to the cell surface and reveals these same densities as a branching structure (doublearrows). A three-dimensional model of the cytoplasmic densities would reveal an anastomosing network. BL, basal (external) lamina; PV, pinocytotic vesicles. x27,000. Lower inset. Higher magnification of cytoplasmic densities attached to the plasma membrane from the area indicated by the rectangle. Note that each cell possesses a basal (external) lamina. In addition, the pinocytotic vesicles can be observed in different stages of their formation, x49,500.
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