Multiple mechanisms of lung surfactant inhibition

We studied the mechanisms by which C16:0 lysophosphatidylcholine (LPC) and albumin inhibit the surface activity of calf lung surfactant extract (CLSE) by using a pulsating bubble apparatus with a specialized hypophase exchang e system, plus adsorption and Wilhelmy balance measurements. In the absence of inhibitors, CLSE (1 mg phospholipid/mL) reached minimum surface tension (gamma(min)) < 1 mN/m within 5 min of bubble pulsation at 20 cycles/min at 37 degrees C. Mixtures of CLSE:LPC had impaired surface activity depending on LPC content: gamma(min) was raised to 5 mN/m by 14 wt % LPC, to 15 mN/m by 25-30 wt % LPC, and to >20 mN/m (67 wt % LPC), even at high CLSE concen trations (3 and 6 mg phospholipid/mL). In contrast, inhibition of CLSE by a lbumin was more easily abolished when surfactant concentration was raised. Mixtures of albumin (3 mg/mL) and CLSE (I mg phospholipid/mL) had gamma(min ) >20 mN/m, but normal values of gamma(min) < 1 mN/m were reached at higher CLSE concentration (3 mg phospholipid/mL) even when albumin concentration was increased 8-fold to 24 mg/mL. In hypophase exchange studies, LPC, but n ot albumin, was able to penetrate preformed CLSE surface films and raise ga mma(min). CLSE surface films with gamma(min) < 1 mN/m were isolated by an i nitial hypophase exchange with saline, and a second exchange with an LPC-co ntaining hypophase raised gamma(min) to similar to 10 mN/m. CLSE surface fi lms retained the ability to reach gamma(min) < I mN/m in analogous hypophas e exchange studies with albumin. The ability of LPC to penetrate surface fi lms of CLSE, although albumin could not, was also demonstrated in adsorptio n experiments in a Teflon dish, where diffusion was minimized by subphase s tirring. Wilhelmy balance experiments also demonstrated that LPC could mix and interact with CLSE or dipalmitoyl phosphatidylcholine in solvent-spread surface films. The ability of LPC or other cell membrane lipids to penetra te interfacial films and raise gamma(min) even at high surfactant concentra tion may increase their inhibitory actions during acute lung injury.