THE BINDING-SITE ON COCHLEAR STEREOCILIA FOR ANTISERA RAISED AGAINST RENAL NA+ CHANNELS IS BLOCKED BY AMILORIDE AND DIHYDROSTREPTOMYCIN

The mechanoelectrical transduction channels on hair cells have been su ggested to be operated by tip links that are stretched when the hair b undle is deflected in the direction of the tallest row of stereocilia. Localising these channels is therefore an important test of this hypo thesis. The transduction channels are known to be amiloride-sensitive and immunogold labelling with antibodies raised against the amiloride- sensitive epithelial Na+ channel from kidney (alpha NaCh), has suggest ed that sites with similar characteristics are located in the region w here the tips of the shorter stereocilia appear to come into contact w ith the sides of the adjacent taller stereocilia rather than being ass ociated directly with the tip links. Now, further immunocytochemical e xperiments have been performed to determine if amiloride and dihydrost reptomycin, both of which can block transduction, can affect this labe lling. Immunofluorescent labelling of the stereocilia is obtained when surface preparations of the organ of Corti are fixed and incubated wi th alpha NaCh followed by an appropriate secondary antibody. This labe lling is abolished by trypsinization prior to fixation but retained if the tissue is pretreated with amiloride and then trypsinized in its p resence, Because amiloride is known to protect amiloride-binding sites from degradation by trypsin, these results suggest that alpha NaCh is revealing amiloride-binding sites on the stereocilia. Similarly, immu nofluorescent labelling of the stereocilia is abolished if cochlear ti ssue is pretreated with dihydrostreptomycin (DHS) and fixed in its pre sence prior to incubation with alpha NaCh. Quantitative analysis of co lloidal gold labelling using transmission electron microscopy shows th at DHS treatment produces a significant reduction in the number of gol d particles on stereocilia, especially in the region of contact betwee n them. These results suggest that anti-Na+ recognises a site with cha racteristics similar to the mechanoelectrical transduction channels.