Ultrastructural localization of Na,K-ATPase in the gerbil cochlea.

Abstract

The transport enzyme Na,K-ATPase has been localized to several different cell types within the inner ear by enzyme cytochemistry, immunohistochemistry, and in situ hybridization. Although these histochemical procedures have provided a fairly consistent pattern of the enzyme's distribution, the precise location of Na,K-ATPase in the cell membrane of some polarized and non-polarized cell types remains uncertain. We addressed this problem in the gerbil cochlea using electron microscopic immunogold cytochemistry. The results confirmed prior ultrastructural localization of Na,K-ATPase along the basolateral plasma membrane of strial marginal and outer sulcus epithelial cells but differed from a previous report in failing to detect the enzyme at the surface of strial intermediate cells. The findings also concurred with and extended previous work in showing immunogold labeling along the entire cell membrane of non-polarized Type II fibrocytes in the inferior portion of the spiral ligament and of subpopulations of fibrocytes in the suprastrial and supralimbal regions. Our observations agreed further with light microscopic immunostaining in displaying uniform gold labeling for Na,K-ATPase in the neurilemma of Type I spiral ganglion neurons, even though these cells are completely ensheathed by myelin. Surprisingly, the enzyme was detectable in the neurilemma of afferent but not that of efferent nerve processes beneath hair cells.

Distribution of the Na,K-ATPase α Subunit in the Rat Spiral Ganglion and Organ of Corti

“…Thus, there does not seem to be a particular subcellular compartment to which NKAα3 expression is restricted in either the central or peripheral nervous system. Our findings are consistent with earlier research using immunocytochemistry that identified the NKAα3 in the SGNs and cochlear nerve in the gerbil (Schulte and Adams 1989;McGuirt and Schulte 1994;Nakazawa et al 1995), rat (ten Cate et al 1994;Peters et al 2001), and mouse (Erichsen et al 1996). NKAα immunoreactivity was localized to the nerve terminals underlying the IHCs and OHCs in the human cochlea (Weber et al 2001).…”

“…3G). Although others have reported expression of the NKAα3 in the myelinated segments (Nakazawa et al 1995) and nodes of Ranvier (Schulte and Adams 1989) of the afferent fibers, our experiments showed NKAα3 immunoreactivity that was most intense in the initial segments of the afferent fibers directly contacting the IHCs and not enriched in the subsequent unmyelinated nodes.…”

“…We found no NKAα1 immunoreactivity in the afferent terminals. Previous studies have reported weak to moderate NKAα1 immunoreactivity in the SGNs and cochlear nerve of the rat (ten Cate et al 1994;Peters et al 2001;Delprat et al 2007) and mouse (Erichsen et al 1996), and one study reports expression of the NKAα in the afferent terminals underlying the OHCs in the gerbil (Nakazawa et al 1995). Although we did not find NKAα1 immunoreactivity in either type I or II afferent terminals, we did see NKAα1 labeling in the spiral ganglion (data not shown) but were unable to identify unequivocally the NKAα1-expressing cells as either the SGNs or ensheathing satellite cells.…”

“…NKAα immunoreactivity was localized to the nerve terminals underlying the IHCs and OHCs in the human cochlea (Weber et al 2001). Ultrastructural analysis attributed NKAα immunoreactivity in the terminals underlying the IHCs to the type I afferent and not lateral efferent terminals in the gerbil (Nakazawa et al 1995). Additional work has shown that NKAα immunoreactivity in the terminals underlying the IHCs and OHCs is due to expression of the NKAα3 in both the gerbil (Schulte and Adams 1989;McGuirt and Schulte 1994) and rat (ten Cate et al 1994).…”

“…Nonetheless, earlier work also reported expression of the NKAα in the neuronal elements of the mammalian cochlea using a variety of techniques, including enzyme cytochemistry (Kerr et al 1982), in situ hybridization (Ryan and Watts 1991), and immunohistochemistry (Schulte and Adams 1989;Iwano et al 1990;McGuirt and Schulte 1994;Schulte and Steel 1994;ten Cate et al 1994;Nakazawa et al 1995;Zuo et al 1995;Erichsen et al 1996;Peters et al 2001;Weber et al 2001).…”