Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB135

Poster Communications

Permeability properties of the proximal tubular tight junction changes along its course and depends on claudin-2 and -10a

N. Himmerkus1, S. Milatz1, T. Breiderhoff2, M. Brinkhus1, C. Quintanova1, D. Müller2, M. Bleich1, D. Günzel3

1. Institute of Physiology, Christian-Albrechts-University Kiel, Kiel, Germany. 2. Department of Pediatric Nephrology, Charité - Universitätsmedizin Berlin, Berlin, Germany. 3. Institute of Clinical Physiology, Charité - Universitätsmedizin Berlin, Berlin, Germany.

In the renal proximal tubule (PT) the paracellular pathway is crucial for bulk reabsorption of water and solutes via the so-called solvent drag mechanism. The perception of this pathway has changed from an unregulated and passive transport route to being a highly regulated and adaptable. It is regulated by the tight junction (TJ) complex and its selectivity is determined by claudin expression. For PT TJ, claudin-2 and claudin-10a are considered to be the main components. Claudin-2 has been described as cation and water permeable and claudin-10a as anion selective. The aim of this study was to investigate paracellular properties along the proximal tubular axis and the contribution of claudin-10a by using isoform-specific claudin-10a knock-out mice (KO). Micro-dissected PTs of KO and of wild-type controls (WT) were investigated in a double-barreled perfusion system. PT was sub-divided in early proximal convoluted tubule (early PCT), intermediate PCT (PCT), late PCT and proximal straight tubule (PST). To investigate paracellular permeability properties diffusion potentials (DPs) were generated by either replacing the basolateral solution by an isosmotic 30 mM NaCl solution or by replacing Cl- by 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. In WT, early PCT showed anion selectivity (PCl/PNa = 1.52 ± 0.07), the segments in between (PCT and late PCT) showed intermediate selectivity and in PST selectivity turned to cation selective (PNa/PCl = 1.26 ± 0.06). PT TJ showed higher Cl- than HCO3- permeability with the highest PCl/PHCO3 in late PCT (1.86 ± 0.25). Early PCT TJ were highly meandering and showed high claudin-10a expression in the TJ. This pattern attenuated gradually along the course of the PT and PST TJ were shorter, straight and dominated by claudin-2 expression. In addition, in this last segment of the PT, the tightening claudin-3 was expressed and co-localized to the TJ. In KO all proximal convoluted parts of PT lost anion selectivity completely but displayed high cation selectivity (PNa/PCl = 2.86 ± 0.45 in early PCT). In PST the differences were less pronounced but qualitative similar (PNa/PCl = 2.00 ± 0.14). KO late PCT, however, now preferred bicarbonate over Cl- (PHCO3/PCl = 1.37 ± 0.25). In all segments of KO, claudin-2 expression dominated TJ staining. In summary, claudin-10a confers anion selectivity with preference of Cl- over bicarbonate to the proximal tubular TJ with the exception of the slightly cation selective PST where claudin-2 dominated. Claudins 2 and 10a and their distribution along the course of the PT are responsible for the distinct properties of the paracellular pathway in this segment.

Where applicable, experiments conform with Society ethical requirements