Ultrastructural localization of Helix pomatia lectin-binding sites in mouse lung elastic fibers

Structural and functional characteristics of lung macro- and microvascular endothelial cell phenotypes

Lung macro- and microvascular endothelial cells exhibit unique functional attributes, including signal transduction and barrier properties. We therefore sought to identify structural and functional features of endothelial cells that discriminate their phenotypes in the fully differentiated lung. Rat lung macro- (PAEC) and microvascular (PMVEC) endothelial cells each exhibited expression of typical markers. Screening for reactivity with nine different lectins revealed that Glycine max and Griffonia (Bandeiraea) simplicifolia preferentially bound microvascular endothelia whereas Helix pomatia preferentially bound macrovascular endothelia. Apposition between the apical plasmalemma and endoplasmic reticulum was closer in PAECs (8 nm) than in PMVECs (87 nm), implicating this coupling distance in the larger store operated calcium entry responses observed in macrovascular cells. PMVECs exhibited a faster growth rate than did PAECs and, once a growth program was initiated by serum, PMVECs sustained growth in the absence of serum. Thus, PAECs and PMVECs differ in their structure and function, even under similar environmental conditions.

Lectin binding beneath the epithelium and in smooth muscle cells in the developing bronchial tree

Components of the subepithelial stratum in developing rat lung reacted transiently with Maclura pomifera agglutinin (MPA) and Aleuria aurantia agglutinin (OFA) conjugated to horseradish peroxidase. These lectins possess selective affinity for and serve to localize glycoconjugates (GCs) with terminal Gal/GalNAc and Fuc, respectively. Staining was strongest with both lectins in the proximal bronchial tree and decreased peripherally to growing buds where it was absent. MPA staining of subepithelial structures decreased from the pseudoglandular through the canalicular period and disappeared by the terminal sac stage. Disappearance of this subepithelial reactivity coincided with appearance of apical MPA-positive glycoconjugate in the canalicular period. OFA stained selectively a layer of flattened cells and a thin extracellular stratum under the epithelium of proximal bronchi in the canalicular period. This lectin affinity extended farther peripherally in the pseudoglandular interval and diminished thereafter. The layer of OFA-positive cells underlying the epithelium was identified immunohistochemically as immature smooth muscle. These muscle cells gained contractile protein while losing surface lectin reactivity during fetal development. The high iron diamine method localized sulfated GC in basement membrane of proximal respiratory passages in the fetal lung. The results attest to the involvement of specific GCs in mediating epithelial-mesenchymal cell interaction during critical stages of bronchial morphogenesis.