Altered channel gating mechanism for CFTR inhibition by a high-affinity thiazolidinone blocker

The thiazolidinone CFTR(inh)-172 was identified recently as a potent and selective blocker of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel. Here, we characterized the CFTR(inh)-172 inhibition mechanism by patch-clamp and short-circuit analysis using cells stably expressing wild-type and mutant CFTRs. CFTR(inh)-172 did not alter CFTR unitary conductance (8 pS), but reduced open probability by > 90% with K(i) approximate to 0.6 muM. This effect was due to increased mean channel closed time without changing mean channel open time. Short-circuit current experiments indicated similar CFTR(inh)-172 inhibitory potency (K(i) approximate to 0.5 muM) for inhibition of Cl(-) current in wild-type, G551D, and G1349D CFTR,however, K(i) was significantly reduced to 0.2 muM for DeltaF508 CFTR. Our studies provide evidence for CFTR inhibition by CFTR(inh)-172 by a mechanism involving altered CFTR gating. (C) 2004 Published by Elsevier B.V. on behalf of the federation of European Biochemical Societies.