Ultrastructure and function of oviduct-uterine junction in Ascaris suum (Nematoda).

Cells comprising the oviduct-uterine junction of the female reproductive tract in Ascaris suum were shown to have a distinctive ultrastructure. The free luminal surface of each epithelial cell was bordered by an electron-dense layer that measured 90 to 120 nm in thickness and could be removed by treatment with pronase. Numerous membrane-bound, filament-containing bodies were present in the cytoplasm near the apical margin. These filaments, measuring 6.5 nm in diameter, coalesce (or condense) to form a larger coiled, or homogeneous, electron-dense substance. These membrane-bound, filament-containing bodies often fused with the plasma membrane and released their contents into the lumen. In other instances, the filamentous arrangements were not membrane bound and remained within the cytoplasm where they formed electron-dense masses adjacent to the plasma membrane. Basal infoldings suggestive of water or ion transport occurred in each cell. Externally, the cells were bordered by a basement lamina and muscle cells.