Molecular mechanism of arachidonic acid inhibition of the CFTR chloride channel

Arachidonic acid inhibits the activity of a number of different Cl^- channels, however its molecular mechanism of action is not known. Here we show that inhibition of cystic fibrosis transmembrane conductance regulator (CFTR) Cl^- channels by arachidonic acid is weakened following mutagenesis of two positively charged pore-lining amino acids. Charge-neutralizing mutants K95Q and R303Q both increased the K_d for inhibition from ∼ 3.5 μM in wild type to ∼ 17 μM. At both sites, the effects of mutagenesis were dependent of the charge of the substituted side chain. We suggest that arachidonic acid interacts electrostatically with positively charged amino acid side chains in the cytoplasmic vestibule of the CFTR channel pore to block Cl^- permeation.