Journal
COMPREHENSIVE PHYSIOLOGY
Volume 2, Issue 3, Pages 1701-1744Publisher
WILEY
DOI: 10.1002/cphy.c110038
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Funding
- Deutsche Forschungsgemeinschaft
- Bundesministerium fur Bildung und Forschung
- European Union
- Prix Louis-Jeantet de Medecine
- Ernst-Jung Preis fur Medizin
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Proteins of the CLC gene family assemble to homo- or sometimes heterodimers and either function as Cl- channels or as Cl-/H+-exchangers. CLC proteins are present in all phyla. Detailed structural information is available from crystal structures of bacterial and algal CLCs. Mammals express nine CLC genes, four of which encode Cl- channels and five 2Cl(-)/H+-exchangers. Two accessory beta-subunits are known: (1) barttin and (2) Ostm1. ClC-Ka and ClC-Kb Cl- channels need barttin, whereas Ostm1 is required for the function of the lysosomal ClC-7 2Cl(-)/H+-exchanger. ClC-1, -2, -Ka and -Kb Cl- channels reside in the plasma membrane and function in the control of electrical excitability of muscles or neurons, in extra- and intracellular ion homeostasis, and in transepithelial transport. The mainly endosomal/lysosomal Cl-/H+-exchangers ClC-3 to ClC-7 may facilitate vesicular acidification by shunting currents of proton pumps and increase vesicular Cl- concentration. ClC-3 is also present on synaptic vesicles, whereas ClC-4 and -5 can reach the plasma membrane to some extent. ClC-7/Ostm1 is coinserted with the vesicular H+-ATPase into the acid-secreting ruffled border membrane of osteoclasts. Mice or humans lacking ClC-7 or Ostm1 display osteopetrosis and lysosomal storage disease. Disruption of the endosomal ClC-5 Cl-/H+-exchanger leads to proteinuria and Dent's disease. Mouse models in which ClC-5 or ClC-7 is converted to uncoupled Cl- conductors suggest an important role of vesicular Cl-accumulation in these pathologies. The important functions of CLC Cl- channels were also revealed by human diseases and mouse models, with phenotypes including myotonia, renal loss of salt and water, deafness, blindness, leukodystrophy, and male infertility. (C) 2012 American Physiological Society. Compr Physiol 2:1701-1744, 2012.
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