The membrane of various cells throughout the body contains CFTR protein channels, which control the transport of ions in and out of cells to maintain pH homeostasis, electrically charged chloride (salt) ions and fluid levels in epithelial tissues. Akabas (2000) describes CFTR as an ATP-binding cassette (ABC) membrane transporter gene. There are 1480 amino acids producing two halves connected by the cytoplasmic regulatory domain (R domain). The two halves create channels that allow negatively charged chloride ions to exit the cell (Thomson and Harris, 2008). As shown in the diagram above, the channel extends from the extracellular area through the cell membrane and narrows at the charge selective filter. it enters the cytoplasm of the cell and terminates after attachment of the anion binding site (Hwang & Sheppard, 2009). Figure 3 shows how the CFTR is composed of five domains; two transmembrane domains (MSDs) are purple and green, two nucleotide binding domains (NBDs) are blue and green, and a single regulatory domain (RD) is red (Hwang & Sheppard, 2009). Recent research by Hwang and Sheppard (2009) explains that MSDs form the selective pore for low conductance anions. Selection so that only chloride ions exit the cell. Gadsby and Nairn (1999) explain that the R domain is the site of phosphorylation. This is the prerequisite for the opening of chloride channels and it is the activity that determines the level of CFTR activation. It controls the transport of chloride ions. The more phosphorylation there is, the higher the probability of channel opening according to Akabas (2000). Multiple locations for phosphorylation include cAMP-dependent protein kinases (PKA) and protein kinase C (PKC) (Gadsby & Narin, 1...... middle of article ......sis /page3.htmConrad, M. (2014). Retrieved from http://www.medicinenet.com/cystic_fibrosis/page3.htmHwang, T., Sheppard, D. (2009). during channel gating diagram Retrieved from http://jp.physoc.org/content/587/10/2151.fullSequeriros, I., Jarad, N. (2012). .com/. pdfs-wm/34276.pdfSequeriros, I., Jarad, N. (2012). Axial lung CT image Retrieved from http://cdn.intechopen.com/pdfs-wm/34276.pdfMarieb, E., Hoehn, K. (2012). McWilliams, T,. Kolbe, J, (2000) 133 (1102), 6-8. 1102/2202/content.pdf Welsh, M., Smith A. (1995) Retrieved from https://www.msu.edu/~luckie/cfarticle.html.