Fig. 6. Dose response of FRET ratio and CBF to cAMP and forskolin in permeabilized human airway epithelial cells. FRET ratio (black) and CBF changes (grey) were recorded from a single ciliated cell, in a previously permeabilized culture that was sequentially perfused on the basolateral side with 20 µM, 50 µM and 100 µM cAMP. Subsequent apical perfusion with 1 µM, 10 µM and 20 µM forskolin are shown. At about 7500 seconds ATP was removed from the basal chamber, which caused a rapid fall of CBF, confirming successful permeabilization of the cell. Thus, this last example does not show the delay of the CBF return to baseline compared to baseline with 20 µM forskolin (see Fig. 9).