The morphology of matrix vesicles produced in experimental arterial aneurysms of rabbits

The morphology and possible modes of matrix vesicle production in the walls of experimental rabbit aneurysms were investigated at an ultrastructural level. The abundant matrix vesicles were mostly circular or oval, and in 95% the largest dimension measured 25 to 130nm. Many had been formed by the disintegration of whole smooth muscle cells or portions thereof but more frequently they were related to and even embedded in the thickened, dystrophic basement membranes of viable smooth muscle cells. Budding was an infrequent feature. Many matrix vesicles were associated with fragments of plasma membrane in the matrix and areas which were possibly interruptions of the plasma membranes. Phagocytosis was seen, but more often the matrix vesicles underwent calcification, and groups of larger closely packed, electron translucent vesicles (80–500nm) indicated lipid accumulation. Experimental aneurysms provide a rich source of matrix vesicles for future investigations.