Nasal potential difference measurements in cystic fibrosis

Examples of nasal PD tracings in a normal patient (Panel A) and in a patient with cystic fibrosis (Panel B). The x-axis is time (minutes) as described, and the y-axis is nasal PD (mV; upward is polarizing). The normal phenotype includes a lower (less polarized) baseline PD in solution #1, a small depolarizing change in PD after amiloride perfusion (solution #2), and a repolarizing PD after perfusion with low-chloride (0 [CI-]) and low-chloride + isoproterenol (solutions #3 and #4: continued presence of amiloride). The cystic fibrosis phenotype includes a higher (more polarized) baseline PD, a large depolarizing change in PD after amiloride perfusion, and absent repolarization after perfusion with 0 [CI-] and 0 [CI-] + isoproterenol. ATP-stimulated PD (solution #5, reflecting stimulation of calcium-activated chloride conductance) is retained in normal subjects and in subjects with cystic fibrosis.