CFTR and cystic fibrosis: We detected noticeable responses in CFTR-mediated short-circuit current (Isc) to cAMP increase by forskolin and the cAMP phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) in WT but not CF IEC monolayer derived transwell cultures (Fig. 4b, **p < 0.001).