title: P2Y4-mediated regulation of Na+ absorption in the Reissner's membrane of the cochlea.
abstract: The epithelial cells of Reissner's membrane (RM) are capable of transporting Na(+) out of endolymph via epithelial Na(+) channel (ENaC). However, much remains to be known as to mechanism of regulation of Na(+) absorption in RM. We investigated P2Y signaling as a possible regulatory mechanism of ENaC in gerbil RM using voltage-sensitive vibrating probe technique and immunohistochemistry. Results showed that UTP induced partial inhibition of the amiloride-sensitive short-circuit current but did not change short-circuit current when applied in the presence of amiloride. The inhibitory effect of UTP was not completely reversible in minutes. The response to UTP was inhibited by reactive blue-2 and 2',3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate but not by suramin or pyridoxalphosphate-6-azophenyl-2', 4'-disulfonic acid, which indicates this P2Y receptor as the P2Y(4) subtype. The phospholipase C (PLC) inhibitors 1-[6[[(17beta)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione and 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine markedly inhibited the effect of UTP on ENaC. In contrast, neither modulation of protein kinase C nor application of 2-aminoehoxydiphenyl borate affected P2Y(4)-mediated inhibition of ENaC. Immunoreactive staining for P2Y(4) was observed in the RM, apical membrane of stria vascularis, spiral ligament, and organ of Corti, including outer hair cell, inner hair cell, outer pillar cell, Deiters' cell, and Hensen cell. These results suggest that the physiological role of P2Y(4) receptor in RM is likely to regulate Na(+) homeostasis in the endolymph. The acute inhibition of ENaC activity by activation of P2Y(4) receptor is possibly mediated by decrease of phosphatidylinositol 4,5-biphosphate in the plasma membrane through PLC activation.
authors.affiliation: Department of Otorhinolaryngology, Seoul National University College of Medicine, Sensory Organ Research Institute, Seoul National University Medical Research Center, Chongro-gu, Seoul 110-744, Korea.
authors.forename: Chang-Hee
authors.initials: CH
authors.lastname: Kim
authors.forename: Hye-Young
authors.initials: HY
authors.lastname: Kim
authors.forename: Ho Sun
authors.initials: HS
authors.lastname: Lee
authors.forename: Sun O
authors.initials: SO
authors.lastname: Chang
authors.forename: Seung-Ha
authors.initials: SH
authors.lastname: Oh
authors.forename: Jun Ho
authors.initials: JH
authors.lastname: Lee
mesh_terms: D000042:Absorption / Q000502:physiology; D000818:Animals; D003051:Cochlea / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004710:Endolymph / Q000187:drug effects / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D053503:Epithelial Sodium Channels / Q000502:physiology*; D005849:Gerbillinae; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2 / Q000502:physiology*; D012964:Sodium / Q000378:metabolism*; D014544:Uridine Triphosphate / Q000494:pharmacology
chemical_list: D053503:Epithelial Sodium Channels; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2; C104749:purinoceptor P2Y4; D012964:Sodium; D014544:Uridine Triphosphate