SURFACTANT-PRODUCING EPITHELIUM IN THE DORSAL PART OF THE CARTILAGINOUS EUSTACHIAN-TUBE OF MICE - LIGHT, TRANSMISSION, AND SCANNING ELECTRON-MICROSCOPIC OBSERVATIONS

The nonciliated area in cartilaginous roof tubothelium of 14 conventio nal mice was examined histologically and classified as a modified tran sitional respiratory epithelium. On the free cell surface numerous sho rt microvilli were found. On the lower roof surface in the midcartilag inous portion and especially near the pharyngeal orifice, a convoluted pattern of ridges and pits was observed. These structural peculiariti es are interpreted as adaptive features, ensuring survival of the cell s in a dynamic tubal environment. On the basis of systematic observati ons of the multilamellar bodies in the cytoplasm resembling the phosph olipid lamellar bodies of pulmonary surfactant, which are discharged i n the tubal lumen and to be found in the pits, it is suggested that th e nonciliated cells are ''specialized'' surfactant-producing tubocytes . The synthesis of surfactant-precursors starts in the basal layer. Di fferent phases of the secretory process were observed in the neighbori ng cells. This finding is related to the cell-cooperation constantly r eleasing the secretory product, and natural cell-turnover. Unlike the previously reported surfactant-producing cells in the lower tubotheliu m of other species, roof tubothelial cells of mice are morphologically similar to type II pneumocytes.