Cell injury and calcification of rat aorta in vitro.

In order to study the mechanism of dystrophic calcification of vascular connective tissue as a result of cell injury, anoxic incubation and organ culture in CMRL 1066 of fresh and freeze thawed rat aorta and serum incubation of fresh rat aorta were performed. Calcium concentration of the culture medium was adjusted to 2.5mM and phosphate to 0.9mM. Calcium depletion from the culture medium continued for 3 weeks and then plateaued. In every experiment, calcification was seen predominantly in association with the membranous cellular degradation products derived from degenerated smooth muscle cells. These were morphologically similar to the matrix vesicles. In the areas of massive necrosis, particularly in the freeze thawed aortic tissue, massive calcification extending to collagen and elastic fibers was seen. Of the various membranous cellular degradation products, mitochondrial inner membrane also appeared to serve as one of the nidi of calcification. Influx of extracellular Ca2+, which results from suppression of ion pumps upon cell injury, to PO4(3-) rich cytosol is thought to play a pivotal role in dystrophic calcification. Phosphatidyl serine located along the inner surface of the plasma membrane or the membranous vesicle may serve as the substrate for heterogeneous nucleation of apatite. Calcification of the cellular degradation products which was more pronounced in freeze thawed aorta is apparently non-energy dependent. Calcification of the elastic and collagen fibers evidently occurs as an extension from the calcified cellular degradation products.