Localization of mRNA encoding the P2X2 receptor subunit of the adenosine 5'-triphosphate-gated ion channel in the adult and developing rat inner ear by in situ hybridization.

Localization of expression of the adenosine 5'-triphosphate (ATP)-gated ion channel P2X2 receptor subunit (P2X2R) in the rat inner ear at different stages of development was achieved by using in situ mRNA hybridization. In the adult, P2X2R mRNA was strongly expressed in many of the cells bordering the cochlear endolymphatic compartment. This included the interdental cells of the spiral limbus, all cells of the inner sulcus and organ of Corti, and cells of the spiral prominence. In the vestibular labyrinth, strong expression was noted in the transitional cells at the base of the crista ampullaris and in the sensory epithelium of the crista and maculae. During development, P2X2R mRNA expression was evident in the precursors of these structures at the earliest period studied, embryonic day 12 (E12). Expression increased during the ontogeny in both the cochlear and the vestibular end organs. In addition, both the spiral and vestibular ganglia showed developmental expression. In contrast to the supporting cells of the organ of Corti, both inner and outer hair cells exhibited P2X2R mRNA only after postnatal day 10 (P10) through P12, concomitant with the onset of hearing. P2X2R expression levels in all cells fell from a maximum at P12-P18 to lower levels in the adult. In the adult, P2X2R mRNA levels were modest in outer hair cells in the basal (high-frequency) encoding region of the cochlea, and inner hair cell labeling was low throughout the cochlea. Reissner's membrane, which maintains an electrochemical barrier between scala vestibuli and scala media, showed considerable expression of P2X2R mRNA in early postnatal development, and expression was maintained at moderate levels in the adult cochlea. These data are consistent with a role for the P2X2R subunit in the processes of labyrinthine development and the regulation of the electrochemical gradients supporting auditory and vestibular sensory transduction.