Glycolipidic component of the epithelial cell coat of the endolymphatic sac

The endolymphatic sac (ES) is thought to synthesize and secrete glycoconjugates such as sulfated glycoproteins into the endolymphatic lumen. Ganglioside Gm1 is a specialized glycolipid containing one sialic acid molecule, which is generally found in the outer leaflet of the cell membrane. This glycolipid, which is known to be a specific receptor for cholera toxin (CT), acts as a membrane transducer and is involved in the modulation of cell metabolism, growth and regeneration. In the present study we identified Gm1 by studying the distribution of the FITC-labeled CT-subunit B in the ES epithelium of adult guinea pigs. Our findings indicate the presence of this ganglioside in the ES, with a predominant localization in the basolateral aspect of the epithelial cell layer. No detectable differences between ES cell types could be identified, whilst the ES distal and intermediate portions showed more reactivity than the proximal portion. This study, which represents the first description of a lipidic glycoconjugate component in the ES, provides evidence in support of the role of the ES in the turnover and regulation of inner ear fluids.