Characterization of constitutive and acid-induced outwardly rectifying chloride currents in immortalized mouse distal tubular cells

Publication date: Available online 5 May 2017
Source:Biochimica et Biophysica Acta (BBA) - General Subjects
Author(s): William C. Valinsky, Rhian M. Touyz, Alvin Shrier
Thiazides block Na⁺ reabsorption while enhancing Ca²⁺ reabsorption in the kidney. As previously demonstrated in immortalized mouse DCT (MDCT) cells, chlorothiazide application induced a robust plasma membrane hyperpolarization, which increased Ca²⁺ uptake. This essential thiazide-induced hyperpolarization was prevented by the Cl⁻ channel inhibitor 5-Nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), implicating NPPB-sensitive Cl⁻ channels, however the nature of these Cl⁻ channels has been rarely described in the literature. Here we show that MDCT cells express a dominant, outwardly rectifying Cl⁻ current at extracellular pH7.4. This constitutive Cl⁻ current was more permeable to larger anions (Eisenman sequence I; I⁻>Br⁻≥Cl⁻) and was substantially inhibited by >100mM [Ca²⁺]o, which distinguished it from ClC-K2/Barttin. Moreover, the constitutive Cl⁻ current was blocked by NPPB, along with other Cl⁻ channel inhibitors (DIDS, FFA). Subjecting the MDCT cells to an acidic extracellular solution (pH<5.5) induced a substantially larger outwardly rectifying NPPB-sensitive Cl⁻ current. This acid-induced Cl⁻ current was also anion permeable (I⁻>Br⁻>Cl⁻), but was distinguished from the constitutive Cl⁻ current by its rectification characteristics, ion sensitivities, and response to FFA. In addition, we have identified similar outwardly rectifying and acid-sensitive currents in immortalized cells from the inner medullary collecting duct (mIMCD-3 cells). Expression of an acid-induced Cl⁻ current would be particularly relevant in the acidic IMCD (pH<5.5). To our knowledge, the properties of these Cl⁻ currents are unique and provide the mechanisms to account for the Cl⁻ efflux previously speculated to be present in MDCT cells.



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