Hyaluronan synthesis by in vitro cultured endolymphatic sac cells

The endolymphatic sac (ELS) has been the subject of investigation for many years and yet its overall function remains unclear. It is believed mainly to be involved in the regulation of endolymph through fluid resorption and secretion of osmotically active substances. The present study was performed using in vitro cultured, fetal ELSs of 18 to 19 day gestational mice, to assess whether the ELS cells can synthesize the osmotically active polysaccharide, hyaluronan (HA). The ELS and portions of the membranous labyrinth were dissected from whole otocyst specimens and placed in 14C glucose-enhanced tissue culture media. A light microscopic (LM), autoradiographic study was performed to assess whether 14C glucose could be incorporated by the tissue into HA. Both the ELS cells and the adjacent cartilage demonstrated radiolabel incorporation within 4 hours of incubation in tissue culture medium, with increased radiolabel density in ELS cells after 24 hours of incubation. HA-specific hyaluronidase (HAase) resulted in removal of HAase-sensitive compounds in the ELS in both 4-hour and 24-hour cultured specimens when compared to adjacent cartilage cells (p = 0.001). Approximately 43 percent of the radiolabel was incorporated into HA in ELS specimens, as compared to a 22 percent HA synthesis in the adjacent cartilage tissue, suggesting preferential synthesis by ELS cells. The dissected murine otocysts demonstrate viability in vitro as measured by their ability to incorporate 14C glucose from tissue culture medium. Under these conditions the cultured ELS demonstrates an ability to synthesize HA. A theory of ELS function is proposed.