Carbohydrate distribution in the living utricular macula of the guinea pig detected by lectins

Carbohydrate distribution in the fresh utricular macula of the guinea pig was analysed using lectins such as Concanavalin A (ConA), Dolichos biflorus agglutinin (DBA), peanut agglutinin (PNA), soybean agglutinin (SBA), Ulex europeus agglutinin (UEA-I) and wheat germ agglutinin (WGA) by means of confocal laser scanning microscopy. The ciliary bundle was strongly reactive to ConA, PNA, SBA and WGA but not to DBA and UEA-I, showing that the ciliary bundle has abundant d-galactose (Gal), N-acetyl-d-glucosamine (GlcNac), d-mannose (Man) and sialic acid(s) (Sia) but not detectable amounts of l-fucose (Fuc) and terminal N-acetyl-d-galactosamine (GalNAc). Similar patterns of lectin bindings with moderate-to-weak intensities were observed on the non-cilial apical surface, on the surface of the otoconia and in the gelatinous layer of the otoconial membrane. On the contrary, the globular substance, a precursor of the otoconia, was scarcely reactive to any lectin examined, implying that it lacks glycoconjugates on its surface. Previous histochemical studies reported that the otoconial membrane possesses a much higher affinity for lectins than does the sensory epithelium (including the cilia) in the vestibular organ. This discrepancy suggests that factors in the preparation process may affect the otoconial membrane or the surface coat of the cilia to change their lectin affinity. Meanwhile, sialidase treatment augmented the affinity of the ciliary bundle for DBA and PNA, indicating that sialylated GalNAc and Gal are present on the vestibular ciliary bundle.