CFTR CL- CHANNEL AND CFTR-ASSOCIATED ATP CHANNEL - DISTINCT PORES REGULATED BY COMMON GATES

The cystic fibrosis transmembrane conductance regulator (CFTR) is a ch loride channel that is regulated by phosphorylation of the R domain an d ATP hydrolysis at two nucleotide-binding domains (NBDs), It is contr oversial whether CFTR conducts ATP or,whether CFTR might be closely as sociated with a separate ATP conductance, To characterize ATP channels associated with CFTR, we analyzed Cl- and ATP single channel-currents in excised inside-out membrane patches from MDCK epithelial cells tra nsiently expressing CFTR, With 100 mM ATP in the pipette and 140 mM Cl - in the bath, ATP channels were associated with CFTR Cl- channels in two-thirds of patches that included CFTR, CFTR Cl- channels and CFTR-a ssociated ATP channels had slope conductances of 7.4 pS and 5.2 pS, re spectively, and had distinct reversal potentials and sensitivities to channel blockers, CFTR-associated ATP channels exhibited slow gating k inetics that depended on the presence of protein kinase A and cytoplas mic ATP, similar to CFTR Cl- channels, Gating kinetics of the ATP chan nels as well as the CFTR Cl- channels were similarly affected by non-h ydrolyzable ATP analogues and mutations in the CFTR R domain and NBDs. Our results indicate that phosphorylation- and nucleotide-hydrolysis- dependent gating of CFTR is directly involved in gating of an associat ed ATP channel. However, the permeation pathways for Cl- and ATP are d istinct and the ATP conduction pathway is not obligatorily associated with the expression of CFTR.