INTRACELLULAR AND EXTRACELLULAR ELEMENTAL COMPOSITION OF THE ENDOLYMPHATIC SAC STUDIED BY X-RAY-MICROANALYSIS

X-ray microanalysis was performed along with light microscopy (LM) on rapidly frozen and cryosectioned endolymphatic sac tissues of adult gu inea pigs, to determine the elemental composition of the different cel l types in this tissue as well as the content of the sac lumen. The mo rphological preservation and spatial resolution of cryo-sectioned endo lymphatic sac was found adequate for the identification of the differe nt cell types of the sac in the transmission electron microscope. Furt her cell type identification was performed by comparing scanning trans mission electron microscopy images with LM images on adjacent serial s ections. X-ray microanalysis demonstrated differences between epitheli al and sub-epithelial cells in the intracellular concentrations of sod ium, chlorine, potassium, calcium, phosphorus and sulphur. Measurement s performed in the lumen of the endolymphatic sac showed elevated sodi um and decreased potassium levels as compared with the known levels of these elements in cochlear or vestibular endolymph. High phosphorus a nd sulphur levels were also found in the endolymph of the sac. Other m orphological and analytical findings on the luminal content point out that otoconial destruction and cleaning of the endolymph from the cell debris and other products such as lipids and proteins take place in t he endolymphatic sac. Our results suggest that the endolymphatic sac p articipates in fluid absorption (osmoregulation), ion transport and ot oconial destruction. The data support the longitudinal flow theory of the endolymph.