Normal CFTR protein channels

Normal Cystic Fibrosis Transmembrane Conductance Regulators (CFTR) transport chloride and bicarbonate ions through the cell membrane of epithelial cells. This helps to regulate fluid and electrolyte balance in the epithelial tissues throughout the body. Epithelial tissue is found in the lungs, sinuses, pancreas, intestines, reproductive system, and sweat glands. When ion flow fails, the ionic concentration of the secretions is modified. The epithelia no longer maintains surface hydration and can cause the duct lumens to obstruct. 

CFTR activity is determined by the quantity of CFTR channels at the cell surface, the amount of time each channel is open (gating), and the amount of ions conducted in a given time in each channel (conductance). CFTR quantity is determined by gene transcription, proper splicing, and mRNA translation, processing and trafficking and the maturation of the CFTR protein and the delivery of it to the cell's surface, and surface stability- the amount of time a CFTR channel is at the surface before being removed and recycled.

According to in vitro experimentation (Bompadre SG, Sohma Y, Li M, Hwang TC. G551D and G1349D), CFTR protein channels have an open probability of ~40%, meaning they are open approximately 40% of the time.