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

Abstract

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.

Physiological Effects Of Extracellular Nucleotides In The Inner Ear

“… 51–53 A number of experiments suggest that this decline originates from the considerable P2X receptor shunt conductance of the various tissues that, in addition to the hair cells, line scala media, with the major exception of the marginal cells of the stria vascularis. 4,54 Analysis of the cochlear partition resistance during injection of ATP into endolymph shows a linear correlation between ATP‐induced decline in EP and decrease in resistance (increased conductance). 33 In cochleas treated with aminoglycoside antibiotics to selectively destroy the hair cells, the effect is still present.…”

“…As noted, the stria vascularis appears as the exception to the general expression of P2X 2 receptors by cells lining scala media. 4,54 Interestingly, the marginal cells within the stria are responsible for the K + influx into scala media and provide the electrical window for the generation of EP by the ion transporters associated with the confluence with the underlying intermediate cell layer. 49 This window into the endolymph occurs via K + channels assembled from KvLQT1 subunits and IsK regulatory subunits, which, in rat and gerbil (and humans), is regulated by a PKC phosphorylation site present on the IsK subunit.…”

“… 31 In contrast, P2X 2 receptor expression is consistently high in both embryonic, neonatal and adult inner ear tissues based on riboprobe in situ hybridization. 54 In the rat, P2X 2 expression is first evident in the otocyst at approximately E12, in presumptive sensorineural epithelium. Expression peaked in the cochlea between P8 and P12, which corresponds with the onset of hearing, before declining somewhat.…”

Immunohistochemical localization of adenosine 5`-triphosphate-gated ion channel P2X2 receptor subunits in adult and developing rat cochlea

“…Several studies have confirmed that the P2X 2 subunit of the ATP‐gated ion channel is abundantly expressed in cochlear tissues. P2X 2 receptor subunits have been identified in hair cells and supporting cells by using the reverse transcription‐polymerase chain reaction (RT‐PCR) technique (Glowatzki et al, 1995; Housley et al, 1995; Brändle et al, 1997, 1999; Housley and Ryan, 1997; Housley et al, 1999) and by in situ hybridization (Housley and Ryan, 1997; Housley et al, 1998b; Parker et al, 1998). P2X 2 subunits also have been detected in Reissner's membrane, which separates the endolymphatic from the perilymphatic compartment (King et al, 1998; Housley et al, 1999).…”

“…Given the putative roles of extracellular ATP and P2 receptors in hearing, it is of clear interest to know the spatiotemporal expression of P2X 2 receptors in the developing labyrinth. Expression of mRNA for P2X 2 was recently localized in the developing rat cochlea by using in situ hybridization (Housley et al, 1998b). Expression was detected in epithelial tissues of the otocyst as early as embryonic day 12 (E12).…”