IMMUNOHISTOCHEMICAL LOCALIZATION OF THE NA-K-CL COTRANSPORTER (NKCC1)IN THE GERBIL INNER-EAR

We mapped the cellular and subcellular distribution of the Na-K-Cl co- transporter (NKCC) in the adult gerbil inner ear by immunostaining wit h a monoclonal antibody (MAb T4) generated against human colon NKCC. H eavy immunolabeling was seen in the basolateral plasma membrane of mar ginal cells in the stria vascularis and dark cells in the vestibular s ystem. Subpopulations of fibrocytes in the cochlear spiral ligament an d limbus and underlying the vestibular neurosensory epithelium also st ained with moderate to strong intensity, apparently along their entire plasmalemma. Because MAb T4 recognizes both the basolateral secretory (NKCC1) and the apical absorptive (NKCC2) isoforms of the co-transpor ter, we employed reverse transcription and the polymerase chain reacti on (RT-PCR) to explore isoform diversity in inner ear tissues. Using N KCC1 and NKCC2 isoform-specific PCR primers based on mouse and human s equences, only transcripts for NKCC1 were detected in the gerbil inner ear. The presence of abundant NKCC1 in the basolateral plasmalemma of strial marginal and Vestibular dark cells confirms conclusions drawn from pharmacological and physiological data. The co-expression of NKCC 1 and Na,K-ATPase in highly specialized subpopulations of cochlear and vestibular fibrocytes provides further evidence for their role in rec ycling K+ leaked or effluxed through hair cells into perilymph back to endolymph, as postulated in current models of inner ear ion homeostas is.