An ATP-dependent inwardly rectifying potassium channel, K-AB-2 (Kir4.1), in cochlear stria vascularis of inner ear: Its specific subcellular localization and correlation with the formation of endocochlear potential

Cochlear endolymph has a highly positive potential of approximately +80 mV. This so-called endocochlear potential (EP) is essential for hearing. Although pivotal roles of K+ channels in the formation of EP have been suggested, the types and distribution of K+ channels in cochlea have not been characterized. Because Ep was depressed by vascular perfusion of Ba2+, an inhibitor of inwardly rectifying K+ (Kir) channels, but not by either 4-aminopyridine or tetraethylammonium, we examined the expression of Kir channel subunits in cochlear stria vascularis, the tissue that is supposed to play the central role in the generation of positive EP. Of 11 members of the Kir channel family examined with reverse transcription-PCR, we could detect only expression of K-AB-2 (Kir4.1) mRNA in stria vascularis. K-AB-2 immunoreactivity was specifically localized at the basolateral membrane of marginal cells but not in either basal or intermediate cells. Developmental expression of K-AB-2 in marginal cells paralleled formation of EP. Furthermore, deaf mutant mice (viable dominant spotting; W-V/W-V) expressed no K-AB-2 in their marginal cells. These results suggest that K-AB-2 in marginal cells may be critically involved in the generation of positive EP.