Chlorzoxazone or 1-EBIO increases Na(+) absorption across cystic fibrosis airway epithelial cells

Previous studies demonstrated that chlorzoxazone or 1-ethyl-2-benzimidazolinone (1-EBIO) enhances transepithelial Cl(-) secretion by increasing basolateral K(+) conductance (G(K)) (Singh AK, Devor DC, Gerlach AC, Gondor M, Pilewski JM, and Bridges RJ. J Pharmacol Exp Ther 292: 778-787, 2000). Hence these compounds may be useful to treat cystic fibrosis (CF) airway disease. The goal of the present study was to determine whether chlorzoxazone or 1-EBIO altered ion transport across Delta F508-CF transmembrane conductance regulator homozygous CFT1 airway cells. CFT1 monolayers exhibited a basal short-circuit current that was abolished by apical amiloride (inhibition constant 320 nM) as expected for Na(+) absorption. The addition of chlorzoxazone (400 microM) or 1-EBIO (2 mM) increased the amiloride-sensitive I(sc) approximately 2.5-fold. This overlapping specificity may preclude use of these compounds as CF therapeutics. Assaying for changes in the basolateral G(K) with a K(+) gradient plus the pore-forming Antibiotic amphotericin B revealed that chlorzoxazone or 1-EBIO evoked an approximately 10-fold increase in clotrimazole-sensitive G(K). In contrast, chlorzoxazone did not alter epithelial Na(+) channel-mediated currents across basolateral-permeabilized monolayers or in Xenopus oocytes. These data further suggest that alterations in basolateral G(K) alone can modulate epithelial Na(+) transport.