Author contributions: M Ju, TS Scott-Ward, J Liu and P Khuituan are co-first author.
Loop diuretics are open-channel blockers of the cystic fibrosis transmembrane conductance regulator with distinct kinetics
Article first published online: 10 DEC 2013
© 2013 The British Pharmacological Society
British Journal of Pharmacology
Volume 171, Issue 1, pages 265–278, January 2014
How to Cite
Ju, M., Scott-Ward, T. S., Liu, J., Khuituan, P., Li, H., Cai, Z., Husbands, S. M. and Sheppard, D. N. (2014), Loop diuretics are open-channel blockers of the cystic fibrosis transmembrane conductance regulator with distinct kinetics. British Journal of Pharmacology, 171: 265–278. doi: 10.1111/bph.12458
- Issue published online: 10 DEC 2013
- Article first published online: 10 DEC 2013
- Accepted manuscript online: 10 OCT 2013 05:31AM EST
- Manuscript Accepted: 26 SEP 2013
- Manuscript Revised: 21 SEP 2013
- Manuscript Received: 11 MAY 2013
- Cystic Fibrosis Trust
- University of Bristol
- Overseas Research Students Awards Scheme of Universities UK
- Strategic Scholarships Fellowships Frontier Research Networks
- Office of the Higher Education Commission of Thailand
- ATP-binding cassette transporter;
- chloride ion channel;
- open-channel blockade;
- epithelial ion transport;
- loop diuretics;
Background and Purpose
Loop diuretics are widely used to inhibit the Na+, K+, 2Cl− co-transporter, but they also inhibit the cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel. Here, we investigated the mechanism of CFTR inhibition by loop diuretics and explored the effects of chemical structure on channel blockade.
Using the patch-clamp technique, we tested the effects of bumetanide, furosemide, piretanide and xipamide on recombinant wild-type human CFTR.
When added to the intracellular solution, loop diuretics inhibited CFTR Cl− currents with potency approaching that of glibenclamide, a widely used CFTR blocker with some structural similarity to loop diuretics. To begin to study the kinetics of channel blockade, we examined the time dependence of macroscopic current inhibition following a hyperpolarizing voltage step. Like glibenclamide, piretanide blockade of CFTR was time and voltage dependent. By contrast, furosemide blockade was voltage dependent, but time independent. Consistent with these data, furosemide blocked individual CFTR Cl− channels with ‘very fast’ speed and drug-induced blocking events overlapped brief channel closures, whereas piretanide inhibited individual channels with ‘intermediate’ speed and drug-induced blocking events were distinct from channel closures.
Conclusions and Implications
Structure–activity analysis of the loop diuretics suggests that the phenoxy group present in bumetanide and piretanide, but absent in furosemide and xipamide, might account for the different kinetics of channel block by locking loop diuretics within the intracellular vestibule of the CFTR pore. We conclude that loop diuretics are open-channel blockers of CFTR with distinct kinetics, affected by molecular dimensions and lipophilicity.