Presence of FXYD6 in the endolymphatic sac epithelia

A homeostasis of the electrochemical properties and volume of the endolymph in the inner ear is essential for hearing and equilibrium sensing and is maintained by ion-transport across an epithelial tissue, the endolymphatic sac. One of the key proteins in the maintenance is Na(+), K(+)-ATPase. Although we previously found that the Na(+), K(+)-ATPase in the sac plays a pivotal role in the control of the endolymphatic volume, the mechanism remains unclear. Therefore, in this study, we examined the expression of FXYD6, a functional modulator of the Na(+), K(+)-ATPase, in the epithelial cells of the endolymphatic sac using various approaches. Laser capture microdissection RT-PCR was used to identify FXYD6 mRNA in the endolymphatic sac. Immunolabeling with the specific antibody showed that FXYD6 was predominantly expressed in the intermediate portion of the endolymphatic sac, and it was colocalized with the Na(+), K(+)-ATPase. Because the Na(+), K(+)-ATPase in this region is known to exhibit a high level of activity, an interaction of FXYD6 with this transporter may be critically involved in the regulation of the characteristics of the endolymph.