Amiloride-sensitive Na⁺ channel-like immunoreactivity in the luminal membrane of some non-sensory epithelia of the inner ear

Some non-sensory epithelia of the inner ear were examined for the localization of immunoreactivity to polyclonal antibodies raised against amiloride-sensitive Na⁺ channels from the bovine kidney. The pre-embedding immunogold technique was used for this purpose. Labelings were found on the membrane of the endolymphatic surface of strial marginal cells, epithelial cells of spiral prominence and Reissner's membrane, and ampullar dark cells. In contrast, no labeling was found on the luminal membrane of mesothelial cells of Reissner's membrane, the cells lining the supra-strial perilymphatic space, transitional cells and ampullar ceiling cells. Since the antibodies used may also label non-selective cation channels and non-functional sodium channel precursors as suggested by others, it was not possible to determine the labelings are solely due to amiloride-sensitive Na⁺ channels. However, the observed result was consistent with the previous studies that amiloride blocks ion transport in strial marginal cells and the semicircular canal. It is therefore likely that the observed labeling includes amiloride-sensitive Na⁺ channels. These labeled ion channels in a variety of epithelial cells lining the endolymphatic space could be important in the inner ear fluid regulation.