Agranular membrane complexes in certain smooth-muscle cells of the lamina propria of the human oviduct. An...

Electron-microscopic examination of 40 tubal specimens from 28 patients revealed the unexpected presence of considerable numbers of smooth-muscle cells in the lamina propria. These "fibromuscular" cells (FM) are branched and have irregular contours; others resemble fibrocytes. All have the identifying features of smooth-muscle cells: from 50 to 75 A filaments with scattered densities, plasmalemmal thickenings, and basement lamina. A prominent smooth-muscle complex (SMC) is associated with certain of these smooth-muscle cells. They are located in all three segments of the tube and concentrated in the 10 cell layers subjacent to the epithelium. These complexes resemble structures in a variety of steroid-synthesizing cells and may possibly play a comparable role in the oviduct.