Bestrophin 1 and 2 are components of the Ca2+ activated Cl- conductance in mouse airways

Ca2+ activated Cl- transport is found in airways and other organs and is abnormal in cystic fibrosis, polycystic kidney disease and infectious diarrhea. The molecular identity of Ca2+ activated Cl- channels (CaCC) in the airways is still obscure. Bestrophin proteins were described to form CaCC and to regulate voltage gated Ca2+ channels. The present Ussing chamber recordings on tracheas of bestrophin 1 knockout (vmd2(-/-)) mice indicate a reduced Cl- secretion when activated by the purinergic agonist ATP (0.1-1 mu M). As two paralogs, best1 and best2, are present in mouse tracheal epithelium, we examined the contribution of each paralog to Ca2+ activated Cl- secretion. In whole cell patch-clamp measurements on primary airway epithelial cells from vmd2(-/-) tracheas, ATP activated Cl- currents were reduced by 50%. Additional knockdown of mbest2 in vmd2(-/-) cells by short interfering RNA further suppressed ATP-incluced Cl- currents down to 20% of that observed in cells from vmd2(+/+) animals. Moreover, RNAi-suppression of both mbest1 and mbest2 reduced CaCC in vmd2(+/+) cells. Direct activation of CaCC by increase of intracellular Ca2+ was also reduced in whole cell recordings of vmd2(-/-) cells. These results clearly suggest a role of bestrophin 1 and 2 for Ca2+ dependent Cl- secretion in mouse airways. (C) 2008 Elsevier B.V. All rights reserved.