diagnostic procedure by site Transepithelial nasal potential difference measurement 2025-06-01T10:28:35Z In vitro, freshly excised airway epithelial tissues can be studied in Ussing chambers, and when the transepithelial electric potential difference (PD) is clamped to zero (short-circuited), basal patterns of ion transport can be directly determined by isotopic measurements of the transepithelial flux of specific electrolytes, including Na+ and Cl- ions. Thus, there are defined correlates of ion flux and bioelectric parameters of active ion transport and tissue (barrier) resistance. Because the PD generated by the airway epithelium reflects the relationship between the magnitude and direction of the net transepithelial active ion transport and the epithelial ion conductance, the transepithelial PD (voltage) serves as an index of ion transport and ionic conductances (permeability). Individuals with cystic fibrosis have a characteristic pattern of bioelectric properties which reflect accelerated Na+ transport (absorption), and (absent) or reduced Cl- secretion.