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

Abstract

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≈0.6 μM. 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≈0.5 μM) for inhibition of Cl⁻ current in wild‐type, G551D, and G1349D CFTR; however, K _i was significantly reduced to 0.2 μM for ΔF508 CFTR. Our studies provide evidence for CFTR inhibition by CFTR_inh‐172 by a mechanism involving altered CFTR gating.