| 14668136 |
Scott-Ward TS, Li H, Schmidt A, Cai Z, Sheppard DN: Direct block of the cystic fibrosis transmembrane conductance regulator Cl (-) channel by niflumic acid. Mol Membr Biol. 2004 Jan-Feb;21(1):27-38.
Niflumic acid is widely used to inhibit Ca (2+) -activated Cl (-) channels. However, the chemical structure of niflumic acid resembles that of diphenylamine-2-carboxylate, a drug that inhibits the cystic fibrosis transmembrane conductance regulator (CFTR) Cl (-) channel. To investigate how niflumic acid inhibits CFTR Cl (-) channel, we studied recombinant wild-type human CFTR in excised inside-out membrane patches. When added to the intracellular solution, niflumic acid caused a concentration- and voltage-dependent decrease of CFTR Cl (-) current with half-maximal inhibitory concentration (K (i)) of 253 microM and Hill co-efficient of approximately 1, at -50 mV. Niflumic acid inhibition of single CFTR Cl (-) channels was characterized by a very fast, flickery block that decreased dramatically current amplitude without altering open-probability. Consistent with these data, spectral analysis of CFTR Cl (-) currents suggested that channel block by niflumic acid was described by the closed <--> open <--> blocked kinetic scheme with blocker on rate (k (on)) = 13.9 x 10 (6) M (-1) s (-1), off rate (k (off))=3348 s (-1) and dissociation constant (K (d)) = 241 microM, at -50 mV. Based on these data, we tested the effects of niflumic acid on transepithelial Cl (-) secretion and cyst growth using type I MDCK epithelial cells. Niflumic acid (200 microM) inhibited cAMP-stimulated, bumetanide-sensitive short-circuit current by 55%. Moreover, the drug potently retarded cyst growth. We conclude that niflumic acid is an open-channel blocker of CFTR that inhibits Cl (-) permeation by plugging the channel pore. It or related agents might be of value in the development of new therapies for autosomal dominant polycystic kidney disease. |
86(1,1,1,6) |