Lectins bind differentially to cilia and microvilli of major and minor cell populations in olfactory and nasal respiratory epithelia

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Abstract
Binding of colloidal gold‐conjugated lectins was studied in cilia and microvilli of rat olfactory and respiratory epithelia. This was done in sections of rapidly frozen, freeze‐substituted specimens embedded in Lowicryl K11M or, for wheat germ agglutinin (WGA) alone, in deep‐etched replicas. Olfactory dendritic endings and cilia labeled with WGA and faintly with soybean agglutinin (SBA); olfactory supporting cell microvilli bound only Dolichos biflorus agglutinin (DBA). Microvilli of an infrequent cell bound peanut agglutinin (PNA), SBA, and WGA. These microvilli labeled more strongly with the last two lectins than the olfactory cilia. Respiratory cilia bound WGA and, somewhat more weakly, PNA; microvilli of ciliated respiratory cells bound all four lectins. Visualization of specific labeling improved after preincubation of sections with neuraminidase, except for DBA where lectin binding was abolished. PNA labeling was seen only after neuraminidase preincubation. The densities of membrane surface particles that labeled with WGA corresponded with those of fracture plane particles in a quantitative freeze‐fracture, deepetch analysis. Therefore, a considerable fraction of the WGA‐bound particles could reflect transmembrane proteins in olfactory dendritic endings and cilia and in respiratory cilia. The possible nature of these particles is discussed.