The clarification of mechanism of regulation of the endolymphatic catio absorption in the outer sulcus cells in the cochlea

2003 Fiscal Year Final Research Report Summary

• Project/Area Number: 14571603
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Otorhinolaryngology
• Research Institution: Tohoku University
• Principal Investigator: CHIBA Toshihiko Tohoku University, graduate School of Medicine, Research Associate, 大学院・医学系研究科, 助手 (70280881)
• Co-Investigator(Kenkyū-buntansha): YOSHIDA Naohiro Tohoku University, Hospital, Research Associate, 医学部附属病院, 助手 (90291260) ; KAWASE Tetuaki Tohoku University, Graduate School of Medicine, Associate professor, 大学院・医学系研究科, 助教授 (50169728)
• Project Period (FY): 2002 – 2003
• Keywords: outer sulcus cells / cochlear K^+ recycling / Kir4.1 potassium channel / P2X(2)ATP receptor / cochlea / endocochlear potential (EP)

Research Abstract

The cation absorption, especially K^+ absorption, in the outer sulcus cells has been demonstrated in our previous literature. In this study, we investigated the K^+ transport mechanism in the outer sulcus cells in detail. We revealed the localization of P2X(2)ATP receptor, which absorb K^+ and Na^+ from endolymph into outer sulcus cells, in the apical membrane of the outer sulcus cells using patch clamp technique. We further investigated the localization of K^+ channels or K^+ transporter in the basolateral membrane of outer sulcus cells using immunohistochemistry, and revealed the localization of Kir4.1, an inward rectifier K^+ channels, in the outer sulcus cells. Kir4.1-like immunoreactivity was found in the stria vascularis, the basolateral plasma membrane of the supporting cells in the organ of Cord and the satellite cells surrounding the spiral ganglion cells, as shown in the previous. In the present investigation, we found new additional information that intense Kir4.1-like immun oreactivity was also distributed in the root process of outer sulcus cells, which is the outermost member of the epithelia cell gap junction system. Immunostaining of outer sulcus cells for Kir4.1 showed a longitudinal gradient between cochlear turns. The outer sulcus cells in the basal turn showed more intense staining than in upper turns. Based on theses results, we hypothesized K^+ ions recycling system in the cochlea as follows. Activation of hair cells by mechanical stimuli induces the influx of K^+ ions from the endolymph to sensory hair cells. The K^+ ions are expelled basolaterally to the extracellular space of the organ of Cord, from which they enter the supporting cells. They move through the epithelial cell gap junction system laterally to the lower part of the spiral ligament. The K^+ ions are also directly moved into outer sulcus cells from endolymph through P2X(2)ATP receptor in the apical membrane. The K^+ ions are released into the extracellular space within the spiral ligament by root process of outer sulcus cells, and are taken up by the Na,K-ATPase and Na-K-Cl cotransporter in the type II fibrocytes. Then, the K^+ are expelled to stria vascularis and recycled back into the endolymph.