Source and role of endolymph macromolecules

Evaluation of some 200 endolymph proteins indicates that they are predomina ntly derived from plasma. However, the profile of endolymph proteins is rem arkably similar to that of perilymph and entirely different from that of pl asma. This supports the current consensus that perilymph rather than plasma is the (direct) source of endolymph. Although the levels of total protein of endolymph is extremely low, a few plasma-derived proteins, such as apoli poproteins J and D, are selectively enriched, conceivably for protection of cell membranes bounding the endolymphatic space. A small number of endolym ph proteins, mostly glycosylated ones, are continually secreted into the en dolymph by specialized epithelial cells, primarily for the maintenance of t he structural and functional integrity of the extracellular superstructures comprising tectorial membrane, otoconial complex (membrane) and cupula. Th ese complex macromolecules cannot be eliminated in the periphery of the com partment, but are transported to the endolymphatic sac for elimination. Imp aired clearance of these negatively charged macromolecules by a dysfunction al endolymphatic sac will contribute to the chemical imbalance of endolymph which accompanies long-standing endolymphatic hydrops, and may be one of t he reasons for the observed loss of function.