DYNAMIC SURFACE-ACTIVITY OF FILMS OF LUNG SURFACTANT PHOSPHOLIPIDS, HYDROPHOBIC PROTEINS, AND NEUTRAL LIPIDS

Surface pressure-area (pi-A) isotherms during dynamic cycling were mea sured for films of dipalmitoyl phosphatidylcholine (DPPC) and column-s eparated fractions of calf lung surfactant extract (CLSE). Emphasis wa s on defining the relative importance of lung surfactant phospholipids (PPL), neutral lipids (N), and hydrophobic proteins (SP) in facilitat ing dynamic respreading and surface tension lowering within the interf acial him itself Solvent-spread films in a Wilhelmy balance were studi ed at 23 degrees and 37 degrees C over a range of cycling rates for in itial concentrations giving both monomolecular and surface-excess film s. A striking finding was that PPL films containing the complete mix o f surfactant phospholipids had greatly improved dynamic respreading co mpared to DPPC, particularly in surface excess films (30 and 15 Angstr om(2)/molecule). Hydrophobic SP gave an additional increase in dynamic respreading in SP&PL compared to PPL films for initial concentrations of 60, 30, and 15 Angstrom(2)/molecule. Neutral lipids also improved respreading slightly in N&PL versus PPL films, but maximum surface pre ssures in N&PL films at 37 degrees C were consistently the lowest of a ny surfactant subfraction. Spread films of SP&PL at 60 and 30 Angstrom (2)/molecule had lower maximum pressures than PPL, but maximum pressur es were slightly larger for SP&PL films at high initial concentration (15 Angstrom(2)/molecule). Supplementary oscillating bubble studies in volving both adsorption and film dynamics at rapid cycling rate (20 cy cles/min) showed that dispersions of CLSE and SP&PL lowered surface te nsion to <1 mN/m, while PPL and N&PL had elevated minimums of 21 mN/m. These results show that secondary surfactant phospholipids in additio n to DPPC are important in the film behavior of pulmonary surfactant, giving improved respreading and overall pi-A isotherms very different from disaturated phospholipids. Hydrophobic SP also increase respreadi ng in the interfacial film, in addition to their known action in incre asing surfactant adsorption. SP may also improve film stability at hig h interfacial concentrations of phospholipid, although they were desta bilizing in more dilute films. Neutral lipids contributed minor increa ses in surfactant respreading, but were consistently detrimental to su rface tension lowering.