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 +8 0 mV. This so-called endocochlear potential (EP) is essential for hear ing. 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 perf usion of Ba2+, an inhibitor of inwardly rectifying K+ (Kir) channels, but not by either 4-aminopyridine or tetraethylammonium, we examined t he expression of Kir channel subunits in cochlear stria vascularis, th e tissue that is supposed to play the central role in the generation o f positive EP. Of 11 members of the Kir channel family examined with r everse transcription-PCR, we could detect only expression of K-AB-2 (K ir4.1) mRNA in stria vascularis. K-AB-2 immunoreactivity was specifica lly 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 muta nt mice (viable dominant spotting; W-V/W-V) expressed no K-AB-2 in the ir marginal cells. These results suggest that K-AB-2 in marginal cells may be critically involved in the generation of positive EP.