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 μM). 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-induced 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.