Carbohydrate content of the endolymphatic sac. A histochemical and lectin-labelling study in the Mongolian gerbil.

A secretory activity has recently been attributed to the endolymphatic sac (ES), as a possible way to contribute to the fluid balance of the entire endolymphatic compartment. Previous histochemical studies have indicated the existence of carbohydrate complexes in the secretory product, both neutral and acidic in nature. A thorough analysis of these compounds in the gerbilline ES was carried out using both transmission electron microscopic (TEM) histochemistry, using dialyzed iron and periodic acid--chromic--silver staining techniques, as well as immunoflourescence with fluorescein-labelled lectins (FITC-lectins). N-acetylglucosamine was found to be one of the major carbohydrate components both of the epithelial layer of the ES and of the luminal precipitate. Proofs for a local secretory activity and its intracellular pathway are presented, suggesting to be involved in the regulation of pressure and volume of inner ear fluids.

Lectin detection of carbohydrates in the endolymphatic sac.

The carbohydrate contents of the guinea pig endolymphatic sac were investigated by the use of lectins. The lumen of the endolymphatic sac was filled with stainable precipitate containing N-acetyl glucosamine, mannose, glucose, galactose and fucose. N-Acetyl galactosamine was also detected but in minute amounts. This composition corresponded to other areas in the inner ear, such as the cupula, the otolithic membrane and the tectorial membrane. The function of these carbohydrates may play an important role in preventing the lumen of the endolymphatic sac from collapsing as well as in regulating transepithelial fluid transport.

Somatostatin (somatostatinlike) immunoreactive cells in the human inner ear.

Certain epithelia of the human inner ear and human endolymphatic sac display somatostatin and/or somatostatin-like immunoreactivity. Histologic sections from 13 human temporal bones and from 15 endolymphatic sacs were studied using the unlabeled antibody peroxidase-antiperoxidase technique. The somatostatin and/or somatostatin-like immunoreactive cells were located exclusively in the covering epithelium of the spiral prominence and in the epithelium of the intermediate and rugosal part of the endolymphatic sac. In the epithelium of the spiral prominence and endolymphatic sac, secretory granules of the same size and appearance as those of intestinal or pancreatic somatostatin-producing cells were demonstrated ultrastructurally. The findings are consistent with a local exocrine, paracrine, and/or endocrine system of the inner ear.

Recent advances in laser microprobe mass analysis (LAMMA) of inner ear tissue.

Maintenance of ionic gradients within the various fluids compartments of the inner ear requires transport active cellular systems at different locations. LAMMA analysis is ideally suited for detection of ions in microquantity on cellular levels overcoming many technical difficulties. The present paper summarizes the results of microprobe analysis obtained with laser induced mass spectrometry (LAMMA) supplemented by X-ray microprobe analysis of epithelial cell layers adjacent to the endolymphatic space in the cochlear duct, in the vestibular organ and in the endolymphatic sac. The possible role of inner ear as well as ocular melanin in the mechanisms of active ion transport is discussed.

Secretory immunoglobulin A in the human endolymphatic sac. An immunohistochemical study.

Presence of immunoglobulin A (IgA) and of secretory component in epithelial cells and in the lumen of the human endolymphatic sac was demonstrated by two different immunohistochemical methods. IgA was also detected in perisaccular plasma cells. The findings connote the existence of a local immune system of the inner ear.

Intracellular and extracellular ion content of the endolymphatic sac.

The Cl- activity in the endolymph of the endolymphatic sac and in the cochlear duct was measured with Cl- sensitive double-barreled microelectrodes. The Cl- activity in the endolymphatic sac fluid was lower than in the cochlear duct. A small, positive, DC potential was recorded in the endolymphatic sac. During anoxia, the DC potential decreased while the Cl- activity in the endolymphatic sac increased. The K/Na ratio in the epithelial cells and subepithelial tissue of endolymphatic sac was measured using the LAMMA technique. The K/Na ratio in the epithelial cells decreased after ethacrynic acid injection (60 mg/kg i.v.). These findings suggest that chloride in the endolymphatic sac is actively transported inward and outward.

Calcite in the statoconia of amphibians: a detailed analysis in the frog Rana esculenta.

The otoconia of Amphibia, especially of the frog Rana esculenta, were studied by X-ray diffraction and scanning electron microscopy (SEM). The SEM studies showed that the membranous labyrinth of Amphibia contains two populations of crystals, which can easily be distinguished by their forms. The X-ray diffraction data indicated that these two populations consist of calcite and aragonite; the endolymphatic sac, the saccule and the lagena contain aragonite, whereas calcite is only found in the otolithic membrane of the utricle. The genetic and functional significance of the existence of two crystalline forms of calcium carbonate in the membranous labyrinth are discussed.

Scanning electron microscopic and x-ray diffraction studies of otoconia in the lizard Podarcis s. sicula.

The otoliths of embryos and young animals of the lizard Podarcis s. sicula were studied by X-ray diffraction and scanning electron microscopy. Two types of crystal that give different X-ray diffraction patterns were found in the membranous labyrinth of Podarcis. The crystals consist of calcite or aragonite and are easily distinguished by scanning electron microscopy because of their different morphology. The two calcium carbonate crystal forms are not mixed at random but are present in the embryo from the very beginning in specific sites. The endolymphatic sac contains aragonite crystals while the saccule contains calcite crystals adjacent to the wall, in addition to a preponderance of aragonite crystals. The utricle and lagena contain only calcite crystals. The presence of two crystal forms of calcium carbonate in the membranous labyrinth are discussed in terms of differing genetic and functional significance.