Final answer:
The CFTR channel opens to allow Cl- ions through when ATP binds and is hydrolyzed, which causes the channel to change shape and permit ion flow down the concentration gradient.
Step-by-step explanation:
The opening of the CFTR channel to allow chloride ions (Cl-) to pass through is triggered by the binding and hydrolysis of ATP (adenosine triphosphate). CFTR is unique among ion channels because it conducts active transport of Cl- ions down their concentration gradient, which is typically a characteristic of passive transport. The ATP molecule provides the energy needed for the CFTR channel to change its shape and open, letting Cl- ions move from areas of high concentration inside the cell to areas of lower concentration outside the cell. This process is essential to maintain the osmotic balance and proper function of various tissues, such as those in the lungs, where CFTR-mediated transport keeps mucus fluid.