Nitric oxide inhibits Na1 absorption across cultured alveolar type II monolayers

Guo, Yi, Michael D. DuVall, John P. Crow, and Sadis Matalon. Nitric oxide inhibits Na1 absorption across cultured alveolar type II monolayers. Am. J. Physiol. 274 (Lung Cell. Mol. Physiol. 18): L369–L377, 1998.—We examined the mechanisms by which nitric oxide (zNO) decreased vectorial Na1 transport across confluent monolayers of rat alveolar type II (ATII) cells grown on permeable supports. Amiloride (10 μM) applied to the apical side of monolayers inhibited ,90% of the equivalent (Ieq) and the short-circuit (Isc) current, with an half-maximal inhibitory concentration (IC50) of 0.85 μM, indicating that Na1 entry into ATII cells occurred through amiloride-sensitive Na1 channels. zNO generated by spermine NONOate and papa NONOate added to both sides of the monolayers decreased Ieq and increased transepithelial resistance in a concentration-dependent fashion (IC50 5 0.4 μM zNO). These changes were prevented or reversed by addition of oxyhemoglobin (50 μM). Incubation of ATII monolayers with 8-bromoguanosine 38,58-cyclic monophosphate (400 μM) had no effect on transepithelial Na1 transport. When the basolateral membranes ofATII cells were permeabilized with amphotericin B (10 μM) in the presence of a mucosal-to-serosal Na1 gradient (145:25 mM), zNO (generated by 100 μM papa NONOate) inhibited ,60% of the amiloride-sensitive Isc. In addition, after permeabilization of the apical membranes, zNO inhibited the Isc [a measure of Na1-K1-adenosinetriphosphatase (ATPase) activity] by ,60%. We concluded that zNO at noncytotoxic concentrations decreased Na1 absorption across cultured ATII monolayers by inhibiting both the amiloride-sensitive Na1 channels and Na1-K1-ATPase through guanosine 38,58-cyclic monophosphate-independent mechanisms.