Abstract
The ClC-7 chloride channel is crucial for bone resorption as it is part of osteoclast acid secretion mechanism, and the ClC-7 gene (ClCN7) KO mice shows sever osteoporosis. Heterozygous mutations in ClCN7 suggest to be responsible for autosomal osteopetorosis type II (ADOII). Although an extracellular acidification dependent Cl− current was reported in ClCN7-expressing Xenopus oocytes, the characterization and structure-functional relationships of ClC-7 channel were still unknown. To clarify the future of ClC-7 channel in osteoclasts, we cloned the ClCN7 in mouse osteoclasts and investigated Cl− currents in ClCN7-expressing HEK293 cells. Extracellular acidification to pH 6.0 evoked strongly Cl− currents in ClCN7-expressing HEK293 cells, but slightly in mock-transfected cells. The acidification dependent Cl− currents showed properties of outward rectification, Ca2+-independency and anion permeability order of Cl−≥I−>Br−>gluconate−, indicating that it is different from swelling-activated Cl− currents. We also detected the expression of ClC-7 channel in membrane fraction of ClCN7 cDNA-transfecting HEK293 cells using Western blot analysis. A point mutation (G215R) of ClCN7 dramatically suppressed the acidification dependent Cl− currents.These results suggested that the ClC-7 chloride channel in osteoclasts may only activate in acidic microenvironment during bone resorption and mutations in ClCN7 may be caused by dysfunction of osteoclasts in ADOII patients. [Jpn J Physiol 55 Suppl:S133 (2005)]
