Pivotal role of anionic phospholipids in determining dynamic behavior of lung surfactant

Phosphatidylglycerol (PG) and phosphatidylinositol (PI) are anionic phospho lipids (APLs) present in lung surfactant of virtually all species studied, although their specific contribution to function is unknown. This study exa mines how APLs influence surfactant monolayer stability and adsorption unde r static and dynamic conditions. Interfacial properties of surfactants reco nstituted with native phospholipids (PL), and phospholipids devoid of anion ic species (DAPL), were characterized by pulsating bubble surfactometry. Me asurements were made for PL and DAPL alone; with 3% surfactant proteins B a nd C (SP-B/C); with SP-B/C and 5% surfactant protein A (SP-A); and with SP- B/C, SP-A and 8% neutral lipids (NL). Equilibrium and dynamic properties of Pt. and DAPL were similar. However, whereas (DAPL + SP-B/C) and (DAPL + SP -B/C + SP-A) mixtures were similar to corresponding PL mixtures with respec t to gamma(equil), they displayed markedly different dynamic behavior. In p articular, the degree of film compression required to reach gamma(min) was significantly increased in DAPL mixtures (80 to 90% area reduction) compare d with PL, although both samples reached gamma(min) < 3.0 dynes/cm. The add ition of NL to (DAPL + SP-B/C + SP-A) produced an increase in gamma(min) to 15 to 20 dynes/cm during dynamic compression, whereas NL had no significan t impact on the behavior of (PL + SP-B/C + SP-A). Purified PG (5% wt/wt) re stored nearly normal dynamic properties to (DAPL + SP-B/C + SPA + NL), wher eas phosphatidylcholine (PC) (5% wt/wt) had no beneficial effect. These res ults suggest that APLs play a critical role in promoting surface film stabi lity during dynamic compression through interactions with nonlipid surfacta nt components, and prevent destabilization of the surface film by cholester ol and other NL.