Fig. 1.

Cell model of the transport proteins in airway epithelial cells that mediate NaCl and water secretion into the periciliary layer in cells expressing wt-CFTR (cystic fibrosis transmembrane conductance regulator). wt-CFTR activates SLC26A4 (Cl⁻/$\mathrm{H}\mathrm{C}{\mathrm{O}}_{\mathrm{3}}^{\mathrm{-}}$ exchanger, also called pendrin) and ANO1 (anoctamine 1, also called TMEM16A) and inhibits ENaC (epithelial Na⁺ channel). NKCC1 (Na⁺-K⁺-2 Cl⁻ cotransporter, also known as SLC12A2), ATP (Na⁺-K⁺-ATPase), and NBC1 (Na⁺-$\mathrm{H}\mathrm{C}{\mathrm{O}}_{\mathrm{3}}^{\mathrm{-}}$ cotransporter, also known as SLC4A2) are located in the basolateral membrane. Na⁺ diffuses across the tight junctions down an electrochemical gradient into the pericilary space. Water is secreted into the periciliary space across the tight junctions and across cells via aquaporin water channels (not shown), due to the osmotic gradient across epithelial cells established by NaCl secretion into the periciliary fluid. [Printed with permission from William Scavone.]