Carbohydrates of the otolith organ in the rainbow trout Oncorhynchus mykiss detected by lectins

A lectin-binding assay was applied to the rainbow trout, Oncorhynchus mykis s, sacculus in order to identify specific sugars in the otolith organ. The binding of biotinylated lectins to the sagitta, otolith membrane and saccul ar epithelial cells was detected by histochemistry, and their binding to th e EDTA-soluble fraction of the otolith matrix and saccular endolymph was de tected by dot-blot analysis. N-Acetylglucosamine (GlcNAc) and mannose (Man) were identified in the otolith matrix with both techniques. These data ind icate that glycoproteins in the otolith matrix have N-glycosidically linked sugar chains. In the otolith membrane, GlcNAc and Man were identified in t he subcupular meshwork, whereas only Man was identified in the gelatinous l ayer. This is in line with the hypothesis that a part of the subcupular mes hwork is incorporated into the otolith as an organic matrix, The saccular e pithelial cells reacted with at least one of the lectins which bound to the otolith matrix. The endolymph had the same reactivity with lectins as the otolith matrix. Thus, we suggest that otolith-matrix carbohydrates are prod uced in the saccular epithelial cells, secreted into the endolymph, and dep osited onto the otolith.