SP-B refining of pulmonary surfactant phospholipid films

Pulmonary surfactant stabilizes the alveoli by lining the air-fluid interfa ce with films that reduce surface tension to near 0 mN/m (gamma(min)). Surf actant protein B (SP-B) enhances the surface activity of surfactant phospho lipids. A captive bubble tensiometer (CBT) was used to study the properties of adsorbed films of dipalmitoylphosphatidylcholine (DPPC) with acidic 1-p almitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (POPG) or neutral 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine with (7:3) and without 1 % dimeric SP-B. SP-B enhanced the adsorption rate of DPPC-containing neutra l or acidic lipid suspensions (1 mg/ml) to a similar extent. Quasi-static c ycling of these films revealed that SP-B significantly decreased the film a rea reduction required to reach gamma(min), for the acidic but not for the neutral system. The results obtained with DPPC-phosphatidylglycerol (PG)-SP -B were consistent with selective DPPC adsorption into the surface monolaye r during film formation. Film area reduction required to reach gamma(min), with this system (with and without calcium) approached that of pure DPPC, s uggesting selective DPPC insertion and PG squeeze-out. Dynamic cycling of s uch films showed that larger film area reductions were required to reach ga mma(min),for the neutral than for acidic system, even after 20 cycles. Fluo rescence microscopy of solvent-spread DPPC-POPG-SP-B planar films revealed highly condensed structures at similar to 25 mN/m, although no specific PG phase-segregated structures could be identified. The study suggests that sp ecific interactions of SP-B with acidic phospholipids of surfactant may be involved in the generation and maintenance of DPPC-rich films in the alveol i.