The lateral intercellular spaces in the endolymphatic sac. A pathway for fluid transport?

The lateral intercellular spaces (LIS) in the epithelium of the endolymphatic sac in different mammals were studied using light and transmission electron microscopy. The reason for the study was that widened LIS are known to occur in fluid transporting epithelia, where they may reflect transepithelial flux of water and solutes. Increased knowledge about LIS may lead to further insight into the mechanisms of endolymph resorption in the endolymphatic sac. The effects of various fixatives, fixation methods and osmolality, and also of surgical labyrinthectomy, on the ultrastructure of LIS were investigated. Widened LIS regularly occurred in the mammalian endolymphatic sac and seem to reflect an in vivo condition. It is thought that LIS may form a pathway for transepithelial water flow in the endolymphatic sac. A hypothetical model of the function of LIS during transepithelial fluid movement in the sac is presented.