Cytoplasmic bar‐like structures of alveolar type II cells: An ultrastructural study in freshly isolated cells from rat lungs

Abstract

Bar-like structures are tubular cytoplasmic inclusions found in situ in pulmonary epithelial type II cells of several animal species. The physiological significance and mode of formation of these inclusions are not fully established. In this paper, we describe bar-like structures as found in freshly isolated type II cells from rat lungs. Pulmonary cells were dissociated from the tissue with elastase and separated on a discontinuous density gradient of Percoll. The complete isolation procedure yielded 17 X 10(6) type II cells per animal (purity = 80%). Either from the crude cell suspensions or the purified preparations, only a small fraction of the type II cell population harbored the inclusions (less than 5%). It is shown that the bounding membranes of the bar-like structures can derive from the endoplasmic reticulum, the nuclear membrane, or the Golgi apparatus. Occasional connections with lamellar bodies were observed, and different levels of complexity in the bar-like structures were also found. The apparent rigid conformation and the orientation of the bar-like structures were taken as evidence for a role of the cytoskeleton in their formation. Because the inclusions do not appear to be new organelles or cellular structures performing a specific function, we propose that their formation may be a transient and limited cellular event in normal cells. However, the stabilization and the generation of the osmiophilic structures, as well as their overproduction, may reflect alterations of the normal physiology of the type II cells.

Platelike and globelike inclusion bodies associated with rough endoplasmic reticulum in alveolar type 2 cells of the sheep

“…This finding was similar to the plate body of sheep type 2 cells found in the present study, although they did not examine the serial sections of the structures. In rat alveolar type 2 cells, Shimura et al (1980) reported barlike structures for the first time, confirmed later by Vincent and Nadeau (1987). The barlike structures of rat type 2 cells were concentrically arranged tubular cytoplasmic inclusions that contained osmiophilic periodic materials, the periodicity of which was 26 A and the width of which was 0.15 to 0.40 pm.…”

“…These findings were consistent with previous reports on the barlike structures in rats (Shimura et al, 1980(Shimura et al, , 1985Vincent and Nadeau, 19861, filamentary tubular inclusions in guinea pigs (Manabe and Ikeda, 19861, rod-shaped structures in dogs (Stephens et al, 19731, and the cisternal bodies in ferrets (Miller et a1.,1982). More recently, Vincent and Nadeau (1987) demonstrated that the barlike structures of rat type 2 cells can be bound to virtually any of the intracellular membrane systems: the Golgi apparatus, the rough endoplasmic reticulum, and the nuclear membrane. This study has shown that most of the plate bodies were connected to each other and to the cisternal body, in addition to the rough endoplasmic reticulum, but no direct continuation with the Golgi apparatus or the nuclear membrane was found.…”

Ultrastructural characteristics of inclusion bodies of type II cells in late embryonic mouse lung

“…tubular inclusions bounded by/associated with ER, and containing a cytoplasmic core and more or less concentrically arranged osmiophilic lamellae. These structures have been observed in type II cells isolated from the rat lung (Vincent and Nadeau 1987), and in rat type II cells studied in situ after stimulation with cholinergic agents like pilocarpine (Shimura et al 1985), as well as in type II cells in several other animal species (see Shimura et al 1985;Vincent and Nadeau 1987). It is possible to imagine that in certain (stimulated) conditions lamellae formation takes place not only in more or less globular forms of secluded cytoplasm, but also in other (e.g.…”