The pulmonary surfactant content of the inclusion bodies found within type II alveolar cells

Abstract

Tricomplex fixation has been used to investigate the contents of the inclusion bodies (cytosomes) found within granular pneumonocytes (pulmonary type II cells) and to compare it morphologically to material lining alveolar surfaces, to surfactant extracted from lung, and to an emulsion of synthetic dipalmitoyl lecithin. After tricomplex fixation, cytosomal contents, isolated surfactant and dipalmitoyl lecithin exhibit lamellar structures with a repeat of about 5.0 nm. These structures are not present if fixation is carried out by means of osmium tetroxide. These observations indicate that cytosomes contain a saturated phospholipid. The similarity of the lamellar form of cytosomal contents to isolated surfactant and to dipalmitoyl lecithin suggests further that this material is surfactant phospholipid and that pulmonary surfactant probably does not contain a nonlipid component which is attached to the hydrophilic ends of the phospholipid molecules. The material lining alveolar surfaces generally does not appear lamellar but exhibits many features of a hexagonal phase. It is thought, however, that cytosomal contents and material lining alveolar surfaces are composed of the same surfactant material since phospholipids can undergo reversible structural changes.