Barttin increases surface expression and changes current properties of ClC-K channels.
The term Bartter syndrome encompasses a heterogeneous group of autosomal recessive salt-losing nephropathies that are caused by disturbed transepithelial sodium chloride reabsorption in the distal nephron. Mutations have been identified in the NKCC2 (Na(+)-K(+)-2Cl(-)) cotransporter and ROMK potassium channel, which cooperate in the process of apical sodium chloride uptake, and ClC-Kb chloride channels, which mediate basolateral chloride release. Recently, mutations in barttin, a protein not related to any known ion transporter or channel, were described in BSND, a variant of Bartter syndrome associated with sensorineural deafness. Here we show that barttin functions as an activator of ClC-K chloride channels. Expression of barttin together with ClC-K in Xenopus oocytes increased ClC-K current amplitude, changed ClC-K biophysical properties, and enhanced ClC-K abundance in the cell membrane. Co-immunoprecipitation revealed a direct interaction of barttin with ClC-K. We performed in situ hybridization on rat kidney slices and RT-PCR analysis on microdissected nephron segments to prove co-expression of barttin, ClC-K1 and ClC-K2 along the distal nephron. Functional analysis of BSND-associated point mutations revealed impaired ClC-K activation by barttin. The results demonstrate regulation of a CLC chloride channel by an accessory protein and indicate that ClC-K activation by barttin is required for adequate tubular salt reabsorption.
Department of Pediatrics, Philipps University of Marburg, Deutschhausstr. 12, 35033 Marburg, Germany. siegfried.waldegger@mailer.uni-marburg.de
Siegfried
S
Waldegger
Nikola
N
Jeck
Petra
P
Barth
Melanie
M
Peters
Helga
H
Vitzthum
Konrad
K
Wolf
Armin
A
Kurtz
Martin
M
Konrad
Hannsjörg W
HW
Seyberth
D000818:Animals; D027321:Anion Transport Proteins; D001477:Bartter Syndrome / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D018118:Chloride Channels / Q000235:genetics / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D009399:Nephrons / Q000378:metabolism; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D017354:Point Mutation; D012333:RNA, Messenger / Q000032:analysis; D029867:Xenopus Proteins; D014982:Xenopus laevis
D027321:Anion Transport Proteins; C440005:BSND protein, human; C489932:CLCNKA protein, human; D018118:Chloride Channels; C486572:Clcnkb protein, rat; D008565:Membrane Proteins; D012333:RNA, Messenger; D029867:Xenopus Proteins; C486688:bsnd protein, rat; C489934:clcnka protein, Xenopus