Question

If the CFTR doesn't work correctly due to a mutation, Cl^- movement is blocked and an abnormally thick sticky mucus is produced on the outside of the cell. This mucus clogs the airways in the lungs, and increases the risk of infection by bacteria. Figure 2 illustrates a mutant CFTR channel in the epithelial cells lining the lung. Suppose the Na^+ channel in the figure was open. Why would more Na^+ enter a cell with mutant CFTR than a cell with normal CFTR? How is solute composition of the mucus layer (outside of cell) affected by mutant CFTR? What membrane protein not shown in this diagram would be important for maintaining ion homeostasis, and why is it important?

Answer 1

.....Suppose the Na+ channel in the figure was open, why would more Na enter the cell with mutant CFTR....

• Na+ ions within cell plasma membrane form sodium ion channels.
• These Na+ ions make the integral membrane proteins.
• These integral membrane proteins form the channels for conduction across the membrane and conduct only positively charged Na+ ions.
• CFTR gene provides a CFTR channel which transports negatively charged chloride ions.
• Allowing of chloride ions in a normal CFTR produces thin, freely flowing mucous which is necessary for proper functioning of digestive system, lungs, reproductive system.
• The movement of chloride ions into and out of cells helps in movement of water and thus production of sweat, mucous, digestive enzymes, saliva and lubrication of eyes in the form of tears.
• Na+ channels do not allow the negatively charged chloride ions to flow within them.
• CFTR also regulates the Na+ ion channels.
• A mutation in CFTR leads to CF, a genetic disease where the transport of chloride ions becomes interrupted.
• Due to gene mutation, the CFTR on the apical surface becomes non-functional and abnormal anion conductance could be seen.
• As the normal CFTR gene regulates conductance of cations across channel, a defect in CFTR gene leads to irregularities in Na+ conductance.