Correlation of Vascular Smooth Muscle Cell Morphology Observed by Scanning Electron Microscopy with Transmission Electron Microscopy

Smooth muscle cell (SMC) morphology was studied in rat large mesenteric artery using scanning electron microscopy (SEM), after removal of connective tissue elements with the OsO4/HCl method. Transmission electron microscopy (TEM) was used to correlate the findings of SEM and to assess the effects of digestion on cell ultrastructure. When viewed with SEM, relaxed SMC possessed a smooth, regular surface morphology with longitudinal striations or grooves. TEM examination of cross-sectional profiles of SMC suggested that these striations corresponded to the arrangement of membrane dense bodies within the SMC. The presence of cell contacts among SMC as observed with SEM were confirmed using TEM. Two types of SMC contacts were found: simple appositional contacts and interdigitations. Gap junctions were not observed between SMC in the media. Although structures suggesting nerve networks were observed in the medial-adventitial border with SEM, this could not be confirmed using TEM as a result of alteration in cell ultrastructure with the digestive method. We conclude that the OsO4/HCl method, although useful for SEM, is not suitable for TEM study, because it caused significant alterations of SMC ultrastructure such that organelles and other structures were no longer evident when viewed with TEM.