Kidney Week

Abstract: TH-OR077

Paracellular Properties of the Cortical Collecting Duct

Session Information

• Na+, K+, Cl- Transport: Regulation and Molecular Mechanisms
  November 02, 2017 | Location: Room 285, Morial Convention Center
  Abstract Time: 05:42 PM - 05:54 PM

Category: Fluid, Electrolytes, and Acid-Base

• 703 Na+, K+, Cl- Basic

Authors

• Himmerkus, Nina, Christian-Albrechts-University Kiel, Kiel, Germany

Nina Himmerkus, MD



http://www.physiologie.uni-kiel.de/en/research/physiology-of-membrane-transport

• Isermann, Julian, Christian-Albrechts-University Kiel, Kiel, Germany

Julian Isermann,

• Jarck, Lieske, Christian-Albrechts-University Kiel, Kiel, Germany

Lieske Jarck,

• Gong, Yongfeng, Washington University School of Medicine, Saint Louis, Missouri, United States

Yongfeng Gong,

• Milatz, Susanne, Christian-Albrechts-University Kiel, Kiel, Germany

Susanne Milatz,

• Hou, Jianghui, Washington University School of Medicine, Saint Louis, Missouri, United States

Jianghui Hou,

• Bleich, Markus, Christian-Albrechts-University Kiel, Kiel, Germany

Markus Bleich,

Background

Collecting duct salt and water transport is involved in the regulation of extracellular volume and blood pressure. Ions are transported either transcellularly or through the paracellular pathway following electrochemical driving forces. Claudins are the major determinants of tight junction permeability. They form the paracellular pathway and claudin-4 and -8 have been discussed to be involved in paracellular chloride transport.

Methods

Cortical collecting ducts (CCD) from principal cell-specific claudin-4 knockout animals (KO) and their respective controls (Ctrl) were investigated under normal diet and low salt diet. CCD were isolated by manual dissection, perfused in vitro and investigated for their basic trans- and paracellular transport properties. Transepithelial voltage (V_te), transepithelial resistance (R_te) and equivalent short circuit current (I’_sc) were measured before and after luminal application of 50 µM amiloride and 100 µM hydrochlorothiazide to inhibit transcellular ion transport. A diffusion potential was generated by changing the basolateral solution from 145 to 30 mM NaCl (isotonic) to test for paracellular ion selectivity and the permeability ratio P_Cl/P_Na was calculated. Immunofluorescence was used to localize and quantify claudin-4 expression along the nephron and particularly in the collecting duct.

Results

Under normal diet CCDs of Ctrl as well as of KO showed similar transcellular amiloride dependent lumen negative V_te. Under inhibition of transcellular transport, however, R_te was lower in KO CCD (111±8 Ωcm²) vs. Ctrl CCD (151±11 Ωcm²), respectively. P_Cl/P_Na values showed chloride selectivity in Ctrl CCD (1.36±0.08) but hardly any selectivity in KO CCD (1.07±0.03). Low salt diet increased amiloride dependent V_te in both genotypes to a similar extend, however, with increased R_te in KO CCD (192±16 Ωcm²) vs. in Ctrl CCD (147±11 Ωcm²), under inhibition of transcellular transport, respectively. P_Cl/P_Na did neither change in Ctrl CCD (1.24±0.05) nor in KO CCD (1.04±0.03). Immunofluorescence confirmed claudin-4 knockout with residual low expression of claudin-4 in intercalated cells.

Conclusion

In summary, claudin-4 is expressed in both, principal and intercalated cells of CCD and claudin-4 deficiency leads to the loss of Cl^- selectivity.

Funding

• Other NIH Support