Na,K-ATPase alpha and beta subunit isoform distribution in the rat cochlear and vestibular tissues.

The distribution of five Na,K-ATPase subunit isoforms (alpha 1, alpha 2, alpha 3, beta 1 and beta 2) in rat cochlear and vestibular tissues was determined by immunocytochemical techniques using subunit isoform specific polyclonal antibodies. The expression of Na,K-ATPase alpha and beta subunit isoforms varied among different cell regions of the inner ear. The alpha 1 subunit isoform was more extensively distributed in all inner ear tissues than the alpha 2 or alpha 3 subunit isoforms. The beta 1 subunit isoform was distributed primarily in spiral ligament and inner hair cells of the cochlea, and in crista ampullaris and macula of the saccule. The beta 2 subunit isoform was most abundant in the stria vascularis, dark cells of the ampullae and utricle. The alpha 1 beta 1 subunit combination of Na,K-ATPase was most commonly found in the spiral ligament, while the alpha 1 beta 2 combination was most abundant in the stria vascularis. Similarly, alpha 1 beta 2 was confined more to the dark cells of the ampullae and utricle. The alpha 3 beta 1 subunit combination of Na,K-ATPase was identified in the inner hair cells of the cochlea and the sensory regions of the vestibular end organs. These observations may reflect functional diversity of Na,K-ATPase in the individual inner ear regions and may provide insight into the differences between fluid and ion transport in the inner ear and that of other transporting tissues. Overall, the distribution pattern further indicates that the different isoform combinations have specific roles.