SURFACE-ACTIVITY OF RABBIT PULMONARY SURFACTANT SUBFRACTIONS AT DIFFERENT CONCENTRATIONS IN A CAPTIVE BUBBLE

This study investigates the surface activity of rabbit pulmonary surfa ctant subfractions at different concentrations in a new pressure-drive n captive bubble surfactometer, which provides more rigorous testing c onditions than heretofore applied to this material. Subfractions were separated by centrifugation of lavage return into a third (P3; 1,000 X average g, 20 min), a fourth (P4; 60,000 X average g, 60 min), and a fifth (P5; 100,000 X average g, 16 h) pellet. At 2.0 mg phospholipid/m l, P3 and P4 demonstrated more rapid adsorption, lower minimum surface tensions on first and subsequent compressions, and lower monolayer co mpressibilities than did P5. This surface activity of P3 and P4 increa sed with concentration between 0.1 and 2.0 mg phospholipid/ml. Adsorpt ion rate constants were similar to 10,000 times faster than desorption constants. We conclude that, in a normal lung, components of P3 and P 4 determine alveolar surface tension. We speculate that under special circumstances even the less surface active P5 could have an important influence at the air-water interface.