Identification of a new outwardly rectifying Cl- channel that belongs to a subfamily of the ClC Cl- channels

Abstract

A new outwardly rectifying Cl- channels (ORCC) that belongs to CIC Cl- channel family has been identified from rat kidney and designated as CIC-5. CIC-5 cDNA encodes a polypeptide of 746 amino acids, which is indicated by hydrophobicity analysis to have structural features that are common of the CIC family. However, the amino acid sequence was weakly homologous to those of other CIC Cl- channels except for CIC-3, which we recently identified as a Ca2+-sensitive OHCC. Northern blot analysis of rat tissues showed that CIC-5 mRNA was predominantly expressed in the kidney and colon. To characterize the functional properties of CIC-5 by whole cell patch-clamp technique, we established the stably transfected CHO-K1 cell line using intranuclear microinjection technique. The transfected cells induced outwardly rectifying and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid- sensitive Cl- currents on whole cell configuration. Following the identification of two highly homologous ORCCs, CIC-3 and CIC-5, a new subfamily encoding ORCC has emerged in the CIC family. Furthermore, CIC-5 was almost identical to a partial sequence of human cDNA that is related to Dent's disease. The molecular structure and functional properties of CIC-5 will provide an important insight into ORCCs and the pathogenesis of Dent's disease.