Differential effects of polycationic protein on Cl- secretory and Na+ absorptive airways

Effects of cationic proteins on electrolyte transport depend on the specific channels and electrochemical driving forces expressed by epithelia. The bioelectric responses of canine tracheal and bronchial epithelia (CTE and CBE, respectively) to a polycationic protein, protamine, were therefore compared. CTE exhibited a brief transient inhibition of shortcircuit current (I(SC)) followed by a prolonged increase of 18 microA/cm2. The apical membrane transiently hyperpolarized and then depolarized by 11 mV. The increase in I(SC) was inhibited by bumetanide. Adenosine 3',5'-cyclic monophosphate, ionomycin, and thapsigargin attenuated the response whereas indomethacin or hypotonic solution had no effect, indicating that latent cystic fibrosis transmembrane regulator Cl- channels were activated. CBE preparations exhibited a 4-microA/cm2 decrease in I(SC), 2 mV hyperpolarization of the apical membrane, and an increase in fractional resistance of the apical membrane on exposure to protamine. These results were consistent with inhibition of the Na+ conductance in the apical membrane of CBE and confirmed that polycationic proteins exert differential effects on Cl- secretory and Na+ absorptive airways.