• 1
    The sulphonylurea drug glibenclamide is a widely used inhibitor of the cystic fibrosis transmembrane conductance regulator (CFTR). To investigate how glibenclamide inhibits CFTR, we studied CFTR Cl channels using excised inside-out membrane patches from cells expressing wild-type human CFTR.
  • 2
    Addition of glibenclamide (10–100 μM) to the intracellular solution caused a concentration-dependent decrease in the open time of CFTR Cl channels, but closed times did not change. This suggests that glibenclamide is an open-channel blocker of CFTR.
  • 3
    Glibenclamide is a weak organic acid. Acidification of the intracellular solution relieved glibenclamide inhibition of CFTR, suggesting that the anionic form of glibenclamide inhibits CFTR.
  • 4
    To begin to identify the glibenclamide binding site in CFTR, we investigated whether glibenclamide competes with either MgATP or Cl ions for a common binding site. Glibenclamide inhibition of CFTR was unaffected by nucleotide-dependent stimulation of CFTR, suggesting that glibenclamide and intracellular MgATP interact with CFTR at distinct sites.
  • 5
    Glibenclamide inhibition of CFTR was voltage dependent and enhanced when the external Cl concentration was decreased. The data suggest that glibenclamide and Cl ions may compete for a common binding site located within a large intracellular vestibule that is part of the CFTR pore.