Some biochemical and physicochemical features of the spiral limbus-basilar membrane-spiral ligament complex

Abstract

It has been shown by immunohistochemical techniques that the predominant collagen of inner ear connective tissues is collagen type II [K. Tomoda et al. Ear Res. Jpn. 15, 199–202 (1984)]. It has now been confirmed by chemical techniques that collagen type II is also abundant in spiral limbus (LIM), basilar membrane (BM), spiral ligament (LIG); in addition, the “minor cartilage collagens” (1 a, 2a , 3a) and collagen type IX are present. No collagen was found in the stria vascularis (SV). In contrast to the situation with LIM and LIG, it was extremely difficult to extract collagen from BM, presumably because the fibers are embedded in a thick, dense “ground substance.” BM was homogenized vigorously with ultrasound and glass micro-beads, then digest with pepsin in order to release the collagen. Protein content of BM ranged from 21% to 28% of dry weight, in rough correspondence with the well-known differences in structural detail of the BM along the extent of the cochlea. In turn, collagen comprises from 36% to 44% of the total protein content. BM also contains appreciable levels of OCP-I and OCP-II, polypeptides previously assumed to be organ of Corti-specific. OCP-I and II are also present in very low concentrations in LIM and LIG, but not in SV. The significance of these findings will be discussed. [Work supported by NSF.]