Kidney Week

Abstract: TH-PO485

Claudin-10a Confers Chloride Permeability to the Tight Junctions of the Proximal Tubule

Session Information

• Fluid and Electrolytes: Basic - I
  October 25, 2018 | Location: Exhibit Hall, San Diego Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Fluid and Electrolytes

• 901 Fluid and Electrolytes: Basic

Authors

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

Nina Himmerkus,

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

Susanne Milatz,

• Breiderhoff, Tilman, Charité - Universitätsmedizin Berlin, Berlin, Germany

Tilman Breiderhoff,

• Brinkhus, Merle, Christian-Albrechts-University Kiel, Kiel, Germany

Merle Brinkhus,

• Quintanova, Catarina, Christian-Albrechts-University Kiel, Kiel, Germany

Catarina Quintanova,

• Müller, Dominik, Charité - Universitätsmedizin Berlin, Berlin, Germany

Dominik Müller,

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

Markus Bleich,

• Günzel, Dorothee, Charité - Universitätsmedizin Berlin, Berlin, Germany

Dorothee Günzel,

Background

In the renal proximal tubule (PT) part of the bulk reabsorption of water and electrolytes takes place via the paracellular pathway. This paracellular pathway is regulated by the tight junction (TJ) complex which consists of a belt like structure around the apical pole of the epithelial cells. In contrast to most other epithelia where this belt is composed of multiple strands forming a meshwork, the PT shows only between one and five strands reflecting its high paracellular permeability. The selectivity of the TJ is mainly determined by the claudin composition of the TJ.

Methods

Micro-dissected PTs of claudin-10a specific knock-out animals (KO) and of wild-type controls (WT) were investigated in a double-barreled perfusion system. Diffusion potentials (DPs) were generated by either replacing the basolateral solution by an isosmotic 30 mM NaCl solution or by replacing Cl^- with HCO₃^-. DP were used to calculate relative permeability (P) ratios for Na⁺, Cl^- and HCO₃^-. Immunofluorescence against claudin-10, claudin-2 and claudin-3 was performed on single isolated tubules.

Results

In WT, the early convoluted part of the proximal tubule (early PCT) showed anion selectivity (P_Cl/P_Na = 1.52 ± 0.07), the last straight part (PST) showed cation selectivity (P_Na/P_Cl = 1.26 ± 0.06) and the convoluted segments in between showed intermediate selectivity. PT TJ showed higher permeability for Cl^- than for HCO₃^- with the highest P_Cl/P_HCO3 (1.86 ± 0.25) in late PCT. In PCT, claudin-10a expression was dominant in the TJ, in PST claudin-2 expression predominated. In addition, in this last segment of the PT, the tightening claudin-3 was expressed and co-localized to the TJ. In KO early PCT, claudin-2 moved to the TJ. Consequently, the early PCT lost anion selectivity completely and displayed high cation selectivity (P_Na/P_Cl = 2.86 ± 0.45). In KO late PCT, P_Cl was lower than P_HCO3 (P_Cl/P_HCO3 = 0.88 ± 0.15). In KO PST differences were less pronounced but qualitatively similar (P_Na/P_Cl = 2.00 ± 0.14; P_Cl/P_HCO3 = 1.05 ± 0.06).

Conclusion

In summary, PT TJ selectivity changes along its axis from anion to cation selectivity. The anion selectivity is further characterized by preference of Cl^- over HCO₃^- and is claudin-10a dependent.