title: Mosaic expression of claudins in thick ascending limbs of Henle results in spatial separation of paracellular Na+ and Mg2+ transport.
abstract: The thick ascending limb (TAL) of Henle's loop drives paracellular Na+, Ca2+, and Mg2+reabsorption via the tight junction (TJ). The TJ is composed of claudins that consist of four transmembrane segments, two extracellular segments (ECS1 and -2), and one intracellular loop. Claudins interact within the same (cis) and opposing (trans) plasma membranes. The claudins Cldn10b, -16, and -19 facilitate cation reabsorption in the TAL, and their absence leads to a severe disturbance of renal ion homeostasis. We combined electrophysiological measurements on microperfused mouse TAL segments with subsequent analysis of claudin expression by immunostaining and confocal microscopy. Claudin interaction properties were examined using heterologous expression in the TJ-free cell line HEK 293, live-cell imaging, and Förster/FRET. To reveal determinants of interaction properties, a set of TAL claudin protein chimeras was created and analyzed. Our main findings are that (i) TAL TJs show a mosaic expression pattern of either cldn10b or cldn3/cldn16/cldn19 in a complex; (ii) TJs dominated by cldn10b prefer Na+over Mg2+, whereas TJs dominated by cldn16 favor Mg2+over Na+; (iii) cldn10b does not interact with other TAL claudins, whereas cldn3 and cldn16 can interact with cldn19 to form joint strands; and (iv) further claudin segments in addition to ECS2 are crucial for trans interaction. We suggest the existence of at least two spatially distinct types of paracellular channels in TAL: a cldn10b-based channel for monovalent cations such as Na+and a spatially distinct site for reabsorption of divalent cations such as Ca2+and Mg2.
authors.affiliation: Institute of Physiology, Christian-Albrechts-University of Kiel, 24098 Kiel, Germany; s.milatz@physiologie.uni-kiel.de.
authors.forename: Susanne
authors.identifier: 0000-0001-9893-0473
authors.initials: S
authors.lastname: Milatz
authors.affiliation: Institute of Physiology, Christian-Albrechts-University of Kiel, 24098 Kiel, Germany.
authors.forename: Nina
authors.identifier: 0000-0002-2910-6728
authors.initials: N
authors.lastname: Himmerkus
authors.affiliation: Institute of Physiology, Christian-Albrechts-University of Kiel, 24098 Kiel, Germany.|Department of Nephrology and Hypertension, Hannover Medical School, 30625 Hannover, Germany.
authors.forename: Vera Christine
authors.initials: VC
authors.lastname: Wulfmeyer
authors.affiliation: Department of Anatomy, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors.forename: Hoora
authors.initials: H
authors.lastname: Drewell
authors.affiliation: Department of Anatomy, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors.forename: Kerim
authors.initials: K
authors.lastname: Mutig
authors.affiliation: Renal Division, Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO 63110.
authors.forename: Jianghui
authors.initials: J
authors.lastname: Hou
authors.affiliation: Institute of Clinical Physiology, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors.forename: Tilman
authors.initials: T
authors.lastname: Breiderhoff
authors.affiliation: Department of Pediatric Nephrology, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors.forename: Dominik
authors.initials: D
authors.lastname: Müller
authors.affiliation: Institute of Clinical Physiology, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Fromm
authors.affiliation: Institute of Physiology, Christian-Albrechts-University of Kiel, 24098 Kiel, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Bleich
authors.affiliation: Institute of Clinical Physiology, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors.forename: Dorothee
authors.initials: D
authors.lastname: Günzel
mesh_terms: D000818:Animals; D057167:Claudins / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D008138:Loop of Henle / Q000378:metabolism* / Q000502:physiology; D008274:Magnesium / Q000378:metabolism*; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D019108:Tight Junctions / Q000378:metabolism
chemical_list: D057167:Claudins; D012964:Sodium; D008274:Magnesium
keywords: FRET; claudin interaction; microperfusion; paracellular ion transport; tight junction