Microarray Analysis of Ion Transport‐Related Genes in Reissner’s Membrane

Abstract

Reissner’s membrane (RM) plays an important role in ion homeostasis of the cochlea; disregulation is thought to be involved in Meniere’s disease, a syndrome that is often treated with glucocorticoids. We demonstrated currents across gerbil RM that could be accounted for by active absorption of Na via apical epithelial Na channels (ENaC), basolateral K channels & Na,K-ATPase [Lee & Marcus, Neurosci. 2003]. We sought molecular evidence for mRNA expression of key elements of this pathway in rat and mouse RM using gene microarray and quantitative RT-PCR. Rat RM showed the same amiloride-sensitive Isc as in gerbil. Dexamethasone (DEX) led to an up-regulation of α-ENaC by a factor of 3 although the α1 subunit of Na,K-ATPase was unchanged. Gene array showed that DEX up-regulated all 3 subunits of ENaC (α: 3x; β : 1.2x; γ : 1.5x) and the α2 subunit of Na,K-ATPase in mouse RM. Transcripts for β 1, 2 & 3-Na,K-ATPase were slightly down-regulated. Other important genes in this pathway (sgk1, glucocorticoid receptor, Nedd 4-2, 11β HSD-1) were also present. RM has also been indirectly implicated in anion transport. Indeed, we found transcripts present for anion transporters (Na/K/2Cl- cotransporter; pendrin; anion exchanger-1,-2,-3,-4; Cl channels) and cAMP regulation (PKA, cAMP-dependent GEF, adenylyl cyclase, phosphodiesterase). These results support our earlier finding of an active amiloride-sensitive Na absorptive function in gerbil RM, extend these results to rat and mouse RM, demonstrate that this pathway is under control of glucocorticosteroids and provide a molecular basis for possible Cl transport function. NIH-NIDCD grants R01-DC00212, NCRR P20 RR17686 & P20 RR16475.