Surfactant protein interactions with neutral and acidic phospholipid films

The captive bubble tensiometer was employed to study interactions of phosph olipid (PL) mixtures of dipalmitoylphosphatidylcholine (DPPC) and 1-palmito yl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or 1-palmitoyl-2-oleoyl-sn-g lycero-3-[phospho-rac-(1-glycerol)] (POPG) at 50 mug/ml with physiological levels of the surfactant protein (SP) A SP-B, and SP-C alone and in combina tion at 37 degreesC. All surfactant proteins enhanced lipid adsorption to e quilibrium surface tension (gamma), with SP-C being most effective. Kinetic s were consistent with the presence of two adsorption phases. Under the con ditions employed, SP-A did not affect the rate of film formation in the pre sence of SP-B or SP-C. Little difference in gamma (min) was observed betwee n the acidic POPG and the neutral POPC systems with SP-B or SP-C with and w ithout SP-A. However, gamma (max) was lower with the acidic POPG system dur ing dynamic, but not during quasi-static, cycling. Considerably lower compr ession ratios were required to generate low gamma (min) values with SP-B th an SP-C. DPPC-POPG-SP-B was superior to the neutral POPC-SP-B system. Altho ugh SP-A had little effect on film formation with SP-B, surface activity du ring compression was enhanced with both PL systems. In the presence of SP-C , lower compression ratios were required with the acidic system, and with t his mixture, SP-A addition adversely affected surface activity. The results suggest specific interactions between SP-B and phosphatidylglycerol, and b etween SP-B and SP-A. These observations are consistent with the presence o f a surface-associated surfactant reservoir which is involved in generating low gamma during film compression and lipid respreading during film expans ion.