Structural features of alveolar wall basement membrane in the adult rat lung.

Abstract

The ultrastructural characteristics of alveolar (ABM) and capillary (CBM) basement membranes in the adult rat lung have been defined using tannic acid fixation, ruthenium red staining, or incubation in guanidine HCI. ABM is dense and amorphous, has 3-to 5-nm filaments in the lamina rara externa (facing the alveolus) that run between the lamina densa and the basal cell surface of the epithelium, has an orderly array of ruthenium red-positive anionic sites that appear predominantly (79%) on the lamina rara externa, and has discontinuities beneath alveolar type II cells but not type I cells that allow penetration of type II cytoplasmic processes into the interstitium of the alveolar wall . The CBM is fibrillar and less compact than ABM, has no lamina rara filaments, and has one fifth the number of ruthenium red-positive anionic sites of ABM that appear predominantly (64%) overlying the lamina densa. Incubation of lung tissue with Flavobacterium heparinurn enzyme or with chondroitinase has shown that ABM anionic sites represent heparan sulfate proteoglycans, whereas CBM anionic sites contain this and other sulfated proteoglycans. The CBM fuses in a focal fashion with ABM, compartmentalizing the alveolar wall into a thick and thin side and establishing a thin, single, basement-membrane gas-exchange surface between alveolar air, and capillary blood. The potential implications of ABM and CBM ultrastructure for permeability, cell differentiation, and repair and morphogenesis of the lung are discussed.

Unique Structural Features That Influence Neutrophil Emigration Into the Lung

“…Based on selective enzyme degradation, ruthenium red appears to react with heparan sulfate proteoglycan, and the LRI of the adult rat lung has one-fifth the number of ruthenium red anionic binding sites compared with the LRE. Interestingly, this difference is not observed in neonatal rats; hence, the diminished reactivity of the LRI appears to be an age-acquired phenotype (26,264,265). In the ABM of adult rats and rabbits, differences in microdomains between type I and II cells have been reported.…”

“…Several other studies (2,26,265) demonstrated discontinuities in the basement membranes of rat type II pneumocytes through which extensions of cytoplasm contact interstitial fibroblasts. Through morphometric analysis they estimated these contacts occur with a frequency of 0.5 and 0.7 per pneumocyte, respectively.…”

“…Beneath the LD lies the lamina fibroreticularis (LF) in which type VII collagen-anchoring fibrils link the LD to the fibrillar (e.g., type III collagen) ECM. In general, the capillary endothelial basement membrane (CBM) is less compact than the ABM, and the layer lying between the capillary lamina densa and the endothelium is referred to as the lamina rara interna (LRI) (212,223,225,264,265).…”

Critical role of RAGE in lung physiology and tumorigenesis: a potential target of therapeutic intervention?

“…Alveolar basal lamina consists of numerous anionic (negatively charged) sites that contain heparan sulfate proteoglycans [83]. The heparin sulfate proteoglycan family includes, among others, collagen XVIII, which is abundant in the lung, although less than collagen IV [84].…”

Dynamic ultrastructure of mouse pulmonary alveoli revealed by an in vivo cryotechnique in combination with freeze‐substitution

“…A close association between erythrocytes and endothelial cells was often seen in the peripheral regions of the alveoli. It may reflect intercellular communications during gas\material exchanges through a very narrow basement membrane (Groniowski & Biczysko, 1964 ;Voccaro & Brody, 1981).…”