The junctions of the spindle-shaped cells of the stria vascularis: a link that completes the barrier between perilymph and endolymph.

It is current opinion that the intercellular spaces of the stria vascularis represent a closed compartment isolated from the endolymph by the tight junctions of the marginal cells and from the perilymph by the junctional complexes of the basel cells. However, it has not yet been investigated whether these two barriers meet at the stria margins toward Reissner's membrane and the spiral prominence. Possible candidates for this sealing could be junctions between the spindle-shaped cells. In the present study freeze-fracture replicas of guinea pig specimens fixed in the presence of filipin were used in order to investigate the junctions of the spindle-shaped cells and to localize the cholesterol in their plasma membrane. Replicas reveal that, below the belt-like apical zonula occludens, the basolateral plasma membranes of the spindle-shaped cells adjacent to each other and to the basal cells are joined over their entire extension by a large number of junctional strands intermingled with numerous filipin-cholesterol-complexes. Gap junctions are present in the meshes formed by these junctional strands. Thus, the plasma membrane of the spindle-shaped cells shows morphological and cytochemical characteristics which indicate that they are the anatomical components completing the barrier isolating the intrastrial compartment from the surrounding fluids.