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  • br Acknowledgements This work was


    Acknowledgements This work was supported by National Natural Science Foundation of China (31701807, 31572000) and Jiangsu Province Science Foundation for Youths (BK20170491).
    Introduction Two Cl− channels of the ClC family, ClC-K1 and ClC-K2 (or their human orthologs ClC-Ka and ClC-Kb, respectively), play a pivotal role in transcellular Cl− Aclacinomycin A in the kidney. Located on the basolateral membrane, they are present throughout the distal nephron [1], [2], [3], but the specific distribution of each ClC-K is still uncertain owing to the lack of isoform-specific antibodies [4]. Mutations in human genes coding for ClC-Kb and the regulatory subunit, Barttin, are responsible for salt-losing tubulopathies, namely Bartter\'s syndrome types 3 and 4, respectively [5], [6], [7]. Rare types of Bartter\'s syndrome can also result from compound mutations in ClC-Kb and ClC-Ka [8]. Renal function has not been investigated in knockout mice for ClC-K2 because they die very early; ClC-K1-knockout mice display impaired urine concentration and nephrogenic diabetes insipidus [9]. In accordance with pathological and physiological data, localization studies suggest that ClC-K2 is highly expressed in the cortical part of the distal nephron, and that ClC-K1 is mostly restricted to the medullary part of the renal tubule [2], [3], [10], [11]. The functional expression of human and rat ClC-K remained controversial until their accessory subunit, Barttin, was identified. It promotes their insertion into the plasma membrane [2], [12]. This discovery made it possible to identify two fundamental properties of ClC-K channels. First, the relative permeability for anions follows the sequence Cl−>Br−>NO3−>I− for ClC-Ka, and Cl−>Br−=NO3−>I− for ClC-Kb; second, the currents are enhanced by a basic external pH and high external calcium concentrations [2], [12]. Interestingly, a glutamate residue that plays a critical role in the protopore gating of other ClC chloride channels is missing in the ClC-K channels, where it is replaced by a valine. For this reason, it has been suggested that the two protopores in the ClC-K dimers are constitutively open. Thus, the common gate (involving both subunits of the dimers) may act as the major regulator of the ClC-K channels. In recent studies on rat ClC-K1, Fahlke\'s group reintroduced the “gating” glutamate and observed profound effects on both conductance and gating [4], [13], [14]. We and others have identified several basolateral chloride channels in different parts of the renal tubule, particularly in the cortical thick ascending limb (CTAL), the distal convoluted tubule (DCT), the connecting tubule (CNT), and the cortical collecting duct (CCD) [15], [16], [17], [18], [19], [20], [21], [22], [23]. Two of these channels, with conductances of 45pS and 9pS, respectively, display properties that are compatible with those of ClC-K chloride channels [24]. Nevertheless, the precise molecular identity of these channels remains elusive, because heterologous expression data are incomplete and heterogeneous. Studies of recombinant channels have involved rat and human ClC-Ks, whereas most of those of the native renal tubule have involved mouse kidney. Furthermore, there are only a few single-channel recordings available for recombinant channels, and they all derive from studies on human ClC-Ka and rat ClC-K1 [4]. In this study, we investigated the properties of recombinant mouse ClC-K1 channels expressed in the presence or absence of mouse Barttin, in an attempt to establish a coherent basis for their correspondence with native chloride channels in the mouse renal tubule.
    Material and methods
    Acknowledgements This work was supported by grants from the Agence Nationale de la Recherche (ANR) (ANR07-PHYSIO-008-2 and BLAN 2010-111201), and by a grant from the BHFZ (Bayerisch-Französisches Hochschulzentrum; FK-13/09). S. L\'Hoste and O. Andrini hold ANR postdoctoral fellowships, and M. Keck, T. Grand and L. Pinelli PhD fellowships from the Ministère de l\'Enseignement Supérieur et de la Recherche. The English text was edited by M. Ghosh.