Organization of rat mesenteric artery after removal of cells of extracellular matrix components.

Rat mesenteric arteries, perfusion fixed in relaxed or contracted conditions, were digested with acid and elastase, bleach (sodium hypochlorite), or alkali to selectively remove collagen, elastin, or cells. Scanning electron microscopy was used to study the three-dimensional organization of the remaining cells or extracellular components. Smooth muscle cells of the tunica media were elongated and circumferentially oriented. Superior mesenteric artery cells had an irregular surface with numerous projections and some ends were forked. Small mesenteric artery cells were spindle shaped with longitudinal surface ridges, and showed extensive corrugations upon contraction. Elastin was present both as laminae and as an interconnected fibrous meshwork. Collagen was arranged in an irregular network of individual fibrils and small bundles of fibrils that formed nests around the cells in both arteries. This irregular arrangement persisted, with no apparent reordering or loss of order, upon contraction. The lack of an ordered arrangement or specialized organization at the cell ends suggests mechanical coupling of the cells to elastin or collagen throughout the length of the cell, allowing for force transmission in a number of directions. The tunica media is thus a "composite" material consisting of cells, elastin, and collagen. The isotropic network of fibers is well suited for transmitting the shearing forces placed on it by contraction of smooth muscle cells and by pressure-induced loading.