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Sodium selectivity of Reissner's membrane epithelial cells.
BMC Physiol. 2011 Feb 01; 11:4.BP

Abstract

BACKGROUND

Sodium absorption by Reissner's membrane is thought to contribute to the homeostasis of the volume of cochlear endolymph. It was previously shown that the absorptive transepithelial current was blocked by amiloride and benzamil. The most commonly-observed target of these drugs is the epithelial sodium channel (ENaC), which is composed of the three subunits α-,β- and γ-ENaC. However, other less-selective cation channels have also been observed to be sensitive to benzamil and amiloride. The aim of this study was to determine whether Reissner's membrane epithelial cells could support parasensory K+ absorption via amiloride- and benzamil-sensitive electrogenic pathways.

RESULTS

We determined the molecular and functional expression of candidate cation channels with gene array (GEO GSE6196), RT-PCR, and whole-cell patch clamp. Transcript expression analysis of Reissner's membrane detected no amiloride-sensitive acid-sensing ion channels (ASIC1a, ASIC2a, ASIC2b) nor amiloride-sensitive cyclic-nucleotide gated channels (CNGA1, CNGA2, CNGA4, CNGB3). By contrast, α-,β- and γ-ENaC were all previously reported as present in Reissner's membrane. The selectivity of the benzamil-sensitive cation currents was observed in whole-cell patch clamp recordings under Cl--free conditions where cations were the only permeant species. The currents were carried by Na+ but not K+, and the permeability of Li+ was greater than that of Na+ in Reissner's membrane. Complete replacement of bath Na+ with the inpermeable cation NMDG+ led to the same inward current as with benzamil in a Na+ bath.

CONCLUSIONS

These results are consistent with the amiloride/benzamil-sensitive absorptive flux of Reissner's membrane mediated by a highly Na+-selective channel that has several key characteristics in common with αβγ-ENaC. The amiloride-sensitive pathway therefore absorbs only Na+ in this epithelium and does not provide a parasensory K+ efflux route from scala media.

Authors+Show Affiliations

Cellular Biophysics Laboratory, Department of Anatomy & Physiology, Kansas State University, Manhattan, KS 66506, USA.No affiliation info availableNo affiliation info available

Pub Type(s)

Comparative Study
Journal Article
Research Support, N.I.H., Extramural

Language

eng

PubMed ID

21284860

Citation

Yamazaki, Muneharu, et al. "Sodium Selectivity of Reissner's Membrane Epithelial Cells." BMC Physiology, vol. 11, 2011, p. 4.
Yamazaki M, Kim KX, Marcus DC. Sodium selectivity of Reissner's membrane epithelial cells. BMC Physiol. 2011;11:4.
Yamazaki, M., Kim, K. X., & Marcus, D. C. (2011). Sodium selectivity of Reissner's membrane epithelial cells. BMC Physiology, 11, 4. https://doi.org/10.1186/1472-6793-11-4
Yamazaki M, Kim KX, Marcus DC. Sodium Selectivity of Reissner's Membrane Epithelial Cells. BMC Physiol. 2011 Feb 1;11:4. PubMed PMID: 21284860.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Sodium selectivity of Reissner's membrane epithelial cells. AU - Yamazaki,Muneharu, AU - Kim,Kyunghee X, AU - Marcus,Daniel C, Y1 - 2011/02/01/ PY - 2010/10/22/received PY - 2011/02/01/accepted PY - 2011/2/3/entrez PY - 2011/2/3/pubmed PY - 2011/11/15/medline SP - 4 EP - 4 JF - BMC physiology JO - BMC Physiol VL - 11 N2 - BACKGROUND: Sodium absorption by Reissner's membrane is thought to contribute to the homeostasis of the volume of cochlear endolymph. It was previously shown that the absorptive transepithelial current was blocked by amiloride and benzamil. The most commonly-observed target of these drugs is the epithelial sodium channel (ENaC), which is composed of the three subunits α-,β- and γ-ENaC. However, other less-selective cation channels have also been observed to be sensitive to benzamil and amiloride. The aim of this study was to determine whether Reissner's membrane epithelial cells could support parasensory K+ absorption via amiloride- and benzamil-sensitive electrogenic pathways. RESULTS: We determined the molecular and functional expression of candidate cation channels with gene array (GEO GSE6196), RT-PCR, and whole-cell patch clamp. Transcript expression analysis of Reissner's membrane detected no amiloride-sensitive acid-sensing ion channels (ASIC1a, ASIC2a, ASIC2b) nor amiloride-sensitive cyclic-nucleotide gated channels (CNGA1, CNGA2, CNGA4, CNGB3). By contrast, α-,β- and γ-ENaC were all previously reported as present in Reissner's membrane. The selectivity of the benzamil-sensitive cation currents was observed in whole-cell patch clamp recordings under Cl--free conditions where cations were the only permeant species. The currents were carried by Na+ but not K+, and the permeability of Li+ was greater than that of Na+ in Reissner's membrane. Complete replacement of bath Na+ with the inpermeable cation NMDG+ led to the same inward current as with benzamil in a Na+ bath. CONCLUSIONS: These results are consistent with the amiloride/benzamil-sensitive absorptive flux of Reissner's membrane mediated by a highly Na+-selective channel that has several key characteristics in common with αβγ-ENaC. The amiloride-sensitive pathway therefore absorbs only Na+ in this epithelium and does not provide a parasensory K+ efflux route from scala media. SN - 1472-6793 UR - https://www.unboundmedicine.com/medline/citation/21284860/Sodium_selectivity_of_Reissner's_membrane_epithelial_cells_ L2 - https://bmcphysiol.biomedcentral.com/articles/10.1186/1472-6793-11-4 DB - PRIME DP - Unbound Medicine ER -