Pflugers Arch 2003 Jan 01;4454:513-21. doi: 10.1007/s00424-002-0957-z.

cAMP-dependent activation of CFTR inhibits the epithelial sodium channel (ENaC) without affecting its surface expression.

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The cystic fibrosis transmembrane conductance regulator (CFTR) is thought to modulate epithelial sodium channel (ENaC) function in various preparations. However, the molecular nature and (patho-)physiological significance of the CFTR/ENaC interaction is still unclear and may vary in different tissues. Co-expression experiments in Xenopus laevis oocytes are a popular approach to investigate a possible functional interaction of CFTR and ENaC but have revealed controversial results. We could confirm previous reports that in oocytes co-expressing ENaC and CFTR the amiloride-sensitive current was reduced during cAMP-mediated stimulation of CFTR. In contrast, co-expression of CFTR per se had no effect on baseline ENaC currents. ENaC with Liddle's syndrome mutation is also inhibited during activation of CFTR, suggesting that the C-terminus of the ENaC beta-subunit is not important for this functional interrelation. Single-channel patch-clamp recordings demonstrated that co-expression of CFTR does not alter the single-channel conductance of ENaC. Using a chemiluminescence assay we demonstrated that the inhibition of ENaC during cAMP-dependent activation of CFTR was not associated with a decrease in ENaC surface expression. We conclude that the inhibitory effect of cAMP-activated CFTR on ENaC is due to a decrease in channel open probability.

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Species referenced: Xenopus laevis
Genes referenced: camp cftr