LOCALIZATION OF MESSENGER-RNA ENCODING THE P2X(2) RECEPTOR SUBUNIT OFTHE 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)-gate d ion channel P2X(2) receptor subunit (P2X(2)R) in the rat inner ear a t different stages of development was achieved by using in situ mRNA h ybridization. In the adult, P2X(2)R mRNA was strongly expressed in man y 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. I n the vestibular labyrinth, strong expression was noted in the transit ional cells at the base of the crista ampullaris and in the sensory ep ithelium of the crista and maculae. During development, P2X(2)R mRNA e xpression was evident in the precursors of these structures at the ear liest period studied, embryonic day 12 (E12). Expression increased dur ing the ontogeny in both the cochlear and the vestibular end organs. I n addition, both the spiral and vestibular ganglia showed developmenta l expression. In contrast to the supporting cells of the organ of Cort i, both inner and outer hair cells exhibited P2X(2)R mRNA only after p ostnatal day 10 (P10) through P12, concomitant with the onset of heari ng. P2X(2)R expression levels in all cells fell from a maximum at P12- P18 to lower levels in the adult. In the adult, P2X(2)R mRNA levels we re modest in outer hair cells in the basal (high-frequency) encoding r egion of the cochlea, and inner hair cell labeling was low throughout the cochlea. Reissner's membrane, which maintains an electrochemical b arrier between scala vestibuli and scala media, showed considerable ex pression of P2X(2)R mRNA in early postnatal development, and expressio n was maintained at moderate levels in the adult cochlea. These data a re consistent with a role for the P2X(2)R subunit in the processes of labyrinthine development and the regulation of the electrochemical gra dients supporting auditory and vestibular sensory transduction. (C) 19 98 Wiley-Liss, Inc.