Changes in hyaluronan synthesis by in vitro cultured endolymphatic sac cells

The endolymphatic sac (ELS) has been implicated in the maintenance of endolymph volume and pressure in the membranous labyrinth through fluid resorption and secretion of osmotically active substances, known as glycosaminoglycans (GAGs). To assess whether the ELS cells synthesize the GAG, hyaluronan (HA), and to further elucidate the secretory function of the ELS, a series of experiments were carried out on in vitro tissue-cultured, fetal murine ELSs. In phase 1 of the investigation, the ELSs that were attached to a small portion of the posterior labyrinth, were resected from whole otocyst specimens and studied in tissue culture. This model was chosen to determine whether a change in endolymph homeostasis affects ELS activity. Radiolabeled 14C glucose incorporation was used to evaluate HA synthesis by ELS cells when cultured in vitro. Approximately 43 percent of the incorporated 14C glucose radiolabel was digested by Streptomyces hyaluronidase (an HA-specific hyaluronidase), suggesting HA synthesis by sac cells. In phase 2 of our experiments, the ELSs were not resected from the otocysts. Instead, they were left attached to intact membranous labyrinths, and whole otocysts were cultured. Studies analogous to those of phase 1, assessing the ability of the ELS cells to incorporate 14C glucose into HA, were performed on these specimens. Streptomyces hyaluronidase treatment of these ELS specimens resulted in a reduction in the removal of radiolabel. Therefore, the ELS cells of intact otocysts incorporated less 14C glucose into HA when compared to the ELS cells of the resected specimens.(ABSTRACT TRUNCATED AT 250 WORDS)