Ultracytochemical Demonstration of Phospholipids in the Surface Layer of the Guinea Pig Eustachian Tube

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Abstract
The surface layer, especially the extracellular mucous blanket, in the eustachian tube of adult guinea pigs, was preserved very effectively with an intravascular perfusion of twice diluted Karnovsky's fixative following overnight incubation in the same fixative containing I % tannic acid. Multilamellar bodies were observed in both mucous lining layers of the tube and the epithelial cells of its lining, but neither reticular nor lattice-like ultrastructures could be detected. Mucous blankets on the pharyngeal portion were composed of an electron-dense surface film and a hypophase. The hypophase was marked heterogenous, and it could hardly be observed on the isthmus. The enzymic digestive method using a purified phospholipase A2 was applied to the middle portion of the tube, and the reaction products, probably phospholipids, could be seen both on the surface film of the lining layers and around some of the dark inclusion bodies in the secretory cells. These findings suggest that such phospholipids may play an important role in reducing surface tension of the eustachian tube.

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