ALVEOLAR TYPE-II CELL CNOS ACTIVITY AND ATP LEVELS ARE INCREASED BY LUNG SURFACTANT OR DPPC VESICLES

In a previous study, we reported that nitric oxide (. NO) affects surf actant synthesis and ATP levels in alveolar type II cells and suggeste d that there is constitutive nitric oxide synthase (cNOS) activity in the cells. In the present study, we performed experiments to confirm f urther the presence of cNOS and to determine the effects of lung sulfa ctant on type II cell . NO and ATP levels. The supernatant from freshl y isolated cells contains . NO (0.26 +/- 0.08 nmol/10(6) cells). Durin g incubation, the cells produce additional . NO at a rate of similar t o 0.3 nmol . 10(6) cells(-1) h(-1). . NO formation is inhibited by 28- 46% by three inhibitors of cNOS and inducible NOS (iNOS), N-G-monometh yl-L-arginine (L-NMMA), L-N5-(1-iminoethyl)ornithine hydrochloride, an d NG-nitro-L-arginine methyl ester, but a specific inhibitor of iNOS, aminoguanidine, has no effect. The production of . NO is reduced in Ca 2+-free medium, is stimulated by the Ca2+ ionophore A-23187, and is in dependent of extracellular L-arginine. One known type of cNOS, endothe lial NOS (eNOS), can be detected in the cells by using Western blot an alysis. Incubation of the cells with lung surfactant leads to a relati vely rapid (similar to 15 min), concentration-dependent increase in . NO formation that reaches levels as high as 238 +/- 14% of control. Th e surfactant effects appear to be caused by its major component, dipal mitoyl phosphatidylcholine (DPPC). Exposure of type II cells to DPPC r esults in maximal increases in . NO formation, ATP content, and Og con sumption, which are 268 +/- 32, 234 +/- 24, and 131 +/- 6% of control, respectively. The DPPC-induced increases in . NO, ATP, and O-2 consum ption, are inhibited by L-NMMA. These results confirm the presence of type II cell cNOS and suggest that it may have a role in the cellular processing of lung surfactant.