Fig. 1.

Pendrin expression in the inner ear. A) The inner ear consists of six sensory organs including the cochlea for hearing, the saccule and utricle for sensing linear acceleration and three ampullae and semicircular canals for sensing angular acceleration. In addition, the inner ear contains a non-sensory structure, the endolymphatic duct and sac. All compartments of the inner ear are lined with epithelial cells and filled with endolymph. The epithelial compartments in the cochlea, utricle and saccule, ampullae and semicircular canals are surrounded by perilymph and epithelial compartment of the endolymphatic sac is surrounded by cerebrospinal fluid. B) Cross-section of one turn of the cochlea. The depicted morphology represents the mature stage of development which is acquired in mice during the second postnatal week. Pendrin is expressed in epithelial cells of the spiral prominence (long arrows) and in spindle cells of stria vascularis (short arrows). C–D) Cross-sections of the saccule or utricle and an ampulla. Pendrin is expressed in transitional cells, which are epithelial cells surrounding the maculae in the saccule and utricle and the cupulae in the ampullae. Transitional cells are engaged in cation absorption. E) Cross-sections of the endolymphatic duct and sac. The depicted simple morphology of the endolymphatic sac represents the late phase of embryonic development in the mouse. During the early postnatal period of development, the morphology of the endolymphatic sac becomes more complex with epithelial ridges and tubular infoldings. The endolymphatic duct penetrates through a canal in the bone, which is called the vestibular aqueduct. Pendrin is most prominently expressed in the apical membrane of mitochondria-rich cells in the endolymphatic sac (arrows). A similar diagram was contributed by the author to another paper [52].