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http://crossmark.crossref.org/dialog/?doi=10.1007/s00424-016-1853-2&domain=pdf
Web End = Pflugers Arch - Eur J Physiol (2016) 468:16091619 DOI 10.1007/s00424-016-1853-2
http://crossmark.crossref.org/dialog/?doi=10.1007/s00424-016-1853-2&domain=pdf
Web End = SENSORY PHYSIOLOGY
The unique ion permeability profile of cochlear fibrocytes and its contribution to establishing their positive resting membrane potential
Takamasa Yoshida1,2,3 & Fumiaki Nin1,2 & Shingo Murakami4,5 & Genki Ogata1,2 &
Satoru Uetsuka1,2,6 & Samuel Choi7,8 & Takashi Nakagawa3 & Hidenori Inohara6 &
Shizuo Komune3,9 & Yoshihisa Kurachi4,5 & Hiroshi Hibino1,2,8
http://orcid.org/0000-0003-0688-1489
Web End = Received: 29 February 2016 /Revised: 30 May 2016 /Accepted: 14 June 2016 /Published online: 25 June 2016 # Springer-Verlag Berlin Heidelberg 2016
Abstract Eukaryotic cells exhibit negative resting membrane potential (RMP) owing to the high K+ permeability of the plasma membrane and the asymmetric [K+] between the extracellular and intracellular compartments. However, cochlear fibrocytes, which comprise the basolateral surface of a multilayer epithelial-like tissue, exhibit a RMP of +5 to +12 mV in vivo. This positive RMP is critical for the formation of an endocochlear potential (EP) of +80 mV in a K+-rich extracellular fluid, endolymph. The epithelial-like tissue bathes fibrocytes in a regular extracellular fluid, perilymph, and apically faces the endolymph. The EP, which is essential for hearing, represents the potential difference across the tissue. Using in vivo electrophysiological approaches, we describe a potential mechanism underlying the unusual RMP of guinea pig fibrocytes. The RMP was +9.0 3.7 mV when fibrocytes were exposed to an artificial control perilymph (n = 28 cochleae). Perilymphatic perfusion of a solution containing low [Na+]
(1 mM) markedly hyperpolarized the RMP to 31.1 11.2 mV (n = 10; p < 0.0001 versus the control, Tukey Kramer test after one-way ANOVA). Accordingly, the EP decreased. Little change in RMP was observed when the cells were treated with a high [K+] of 30 mM (+10.4 2.3 mV; n = 7; p = 0.942 versus the control). During the infusion of a low [Cl] solution (2.4 mM), the RMP moderately hyperpolarized to 0.9 3.4 mV (n = 5; p < 0.01 versus the control), although the membranes, if governed by Cl permeability, should be depolarized. These observations imply that the fibrocyte membranes are more permeable to Na+ than K+ and Cl, and this unique profile and [Na+] gradient across the membranes contribute to the positive RMP.
Keywords Endocochlear...