sodium selectivity of reissners membrane epithelial cells赖斯纳氏膜上皮细胞钠选择性.pdf

Yamazaki et al. BMC Physiology 2011, 11:4 /1472-6793/11/4 RESEARCH ARTICLE Open Access Sodium selectivity of Reissner’s membrane epithelial cells 1,2 1 1* Muneharu Yamazaki , Kyunghee X Kim , Daniel C Marcus 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 a-,b- and g-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, a-,b- and g-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 w