Characterization of the outer hair cell's lateral wall membranes

We examined the properties of outer hair cell (OHC) lateral wall membranes by application of 2 fluorescent membrane probes. The markers, C6-NBD-Ceramide and DiOC6, have been used in other cell types to label Golgi apparatus and endoplasmic reticulum, respectively. In living isolated OHCs NBD-Ceramide demonstrated uninterrupted fluorescence along the OHC lateral wall, while DiOC6 labeling proved punctate and notably less uniform in this region. In aldehyde-fixed isolated OHCs both probes exhibited distinct, continuous lateral wall fluorescence. Fixed preparations of the organ of Corti labeled with each probe demonstrated diffuse fluorescence throughout the inner hair cell cytoplasm unlike the uniform, circumferential lateral wall fluorescence seen in OHCs. OHCs exposed to salicylate following NBD-Ceramide labeling displayed patchy, less distinct labeling along the OHC lateral wall. The thickness of lateral wall fluorescence in salicylate exposed cells was 49% greater than control OHCs. We interpreted the salicylate induced change in lateral wall labeling as a fluorescent representation of previously described ultrastructural dilatation and vesiculation of the subsurface cisternae. The distribution of these 2 fluorescent probes along OHC lateral wall membranes suggests that the OHC's subsurface cisternae are neither Golgi nor ER, but share characteristics of both.