Barttin modulates trafficking and function of ClC-K channels.
Barttin is an accessory subunit of a subgroup of ClC-type chloride channels expressed in renal and inner ear epithelia. In this study, we examined the effects of barttin on two ClC-K channel isoforms, rat ClC-K1 and human ClC-Kb, using heterologous expression, patch clamping, confocal imaging, and flow cytometry. In the absence of barttin, only a small percentage of rClC-K1 and hClC-Kb channels are inserted into the plasma membrane. Coexpression of barttin enhances surface membrane insertion and furthermore modifies permeation and gating of ClC-K channels. hClC-Kb channels are nonfunctional without barttin and require the coexpressed accessory subunit to become anion conducting. In contrast, rClC-K1 channels are active without barttin, but at the cost of reduced unitary conductance as well as altered voltage dependence of activation. We mapped the separate functions of barttin to structural domains by a deletion analysis. Whereas the transmembrane core is necessary and sufficient to promote ClC-K channel exit from the endoplasmic reticulum, a short cytoplasmic segment following the second transmembrane helix modifies the unitary conductance. The entire cytoplasmic carboxyl terminus affects the open probability of ClC-K channels. The multiple functions of barttin might be necessary for a tight adjustment of epithelial Cl(-) conductances to ensure a precise regulation of body salt content and endocochlear potential.
Scholl
Ute
U
Abteilung Neurophysiologie, Medizinische Hochschule Hannover, 30625 Hannover, Germany.
Hebeisen
Simon
S
Janssen
Audrey G H
AG
Müller-Newen
Gerhard
G
Alekov
Alexi
A
Fahlke
Christoph
C
D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D018118:Chloride Channels / Q000737:chemistry / Q000502:physiology*; D003593:Cytoplasm / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D017353:Gene Deletion; D006801:Humans; D007668:Kidney / Q000378:metabolism; D008565:Membrane Proteins / Q000502:physiology*; D008954:Models, Biological; D009154:Mutation; D011487:Protein Conformation; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary
C440005:BSND protein, human; C489932:CLCNKA protein, human; C412733:CLCNKB protein, human; D018118:Chloride Channels; D008565:Membrane Proteins; D020033:Protein Isoforms