CFTR and cystic fibrosis: This reflects hyper-absorption of Na+, and likely reflects higher than normal ENaC activity in CF patients due to the absence of the inhibitory regulation of the ENaC channel by the CFTR protein.34,36,52 In summary, the trans-epithelial potential of a CF patient is high under baseline conditions, is almost entirely amiloride-sensitive, and fails to increase in response to cAMP/PKA stimulation in the presence of amiloride.