Osmiophilia of the saturated phospholipid, dipalmitoyl lecithin, and its relationship to the alveolar lining layer of the mammalian lung.

Abstract

AbstractThe appearance and the osmiophilic properties of synthetic dipalmitoyl lecithin (DPL) were characterized under various conditions. It was shown that DPL appeared as 50 Å round to oval dots and lamellae of 50 Å periodicity when negatively stained with phosphotungstate. Osmium‐vapor treatment of a DPL suspension produced negatively outlined DPL, similar to the images obtained with negative staining with phosphotungstate. A mixture of ethanol, osmium and DPL showed the heavily osmiophilic lamellae of DPL in thin sections. The periodicity measures 42 Å. These results are the first in the literature to reveal the osmiophilic nature of saturated dipalmitoyl lecithin.Prolonged washing after both glutaraldehyde and osmium fixation of lung tissue, thus eliminating the chance for interaction among osmium tetroxide, ethanol and saturated phospholipid, resulted in a loss of the heavily osmiophilic surface film that has been reported to be present after routine tissue processing. Secondary osmication of the washed lung with a mixture of osmium tetroxide and ethanol solution brought about striking osmiophilia of the surface film, which was lamellar and was identical to synthetic DPL in its periodicity.It is suggested that the osmiophilic line observed after routine tissue processing is saturated phospholipid that binds osmium during the process of ethanol dehydration immediately following osmium fixation.