Ultrastructural features of the innervation and smooth muscle of the rabbit facial vein, and their relationship to function.
The purpose of this study was to determine to what extent the ultrastructure of the intramedial plexus of autonomic nerves and the smooth muscle of the rabbit facial vein could be correlated with the functional properties of this vessel. The mean observed widths of neuromuscular clefts were 250 nm in untreated control vessels, 260 in the dilated vein, and 390 in the contracted vein. Variation in the plane of section and in cell surface contours may lead to overestimation of cleft width, particularly in contracted vessels; the conclusion was reached, therefore, that the actual mean cleft width in this vessel, which may be closer to 200 nm, is relatively narrow in comparison with other blood vessels. There is probably little significant variation in cleft width with changes in vessel diameter. This narrow cleft correlates with the pronounced neurogenic response of this vessel. The smooth muscle cells of the facial vein appear to contain a relatively small amount of sarcoplasmic reticulum, which may be related to the dependence of maintained tone on extracellular calcium. Areas of close apposition of cell surfaces, with gaps of approximately 15 nm, may be related to propagation of electrical activity from one smooth muscle cell to another.
- Copyright © 1981 by American Heart Association