Scanning electron microscopy of vascular smooth muscle cells from rat muscular arteries

The use of scanning electron microscopy (SEM) for the examination of medial smooth muscle cells (SMC) is limited by the presence of connective tissue mass in the adventitia obscuring the detailed structure of the SMC. This study deals with the description of a method which selectively removes the connective tissue, allowing three dimensional observation of SMC using SEM. A number of methods were tried. One method involving post fixation with 2% OsO4 used in conjunction with HCl proved most successful in removing the extracellular matrix of large mesenteric arteries from spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto normotensive rats (WKY). In both SHR and WKY, the spindle-shaped cells are circumferentially oriented, and ran parallel to one another and formed a continuous compact medial layer with a number of intercellular junctions being evident. Surface morphology of SMC changed between relaxed and contracted states. Relaxed SMC had a smooth regular surface with very fine longitudinal grooves or striations running parallel to the cell long axis. Contracted SMC possessed regular transverse folds on its surface giving a corrugated appearance. The nerve network possessed a fishnet appearance with many triangular bulges at nerve branch points. The internal elastic laminae showed longitudinal furrows and fenestrations, the number of which varied from vessel to vessel. In the superior mesenteric artery, the SMC were circular and helically arranged. Longitudinally and diagonally arranged SMC were evident at bifurcations. Mesenteric veins consisted of one layer of flattened circular SMC that ran parallel to one another and formed a compact and complete medial layer.