Surface properties of binary mixtures of some pulmonary surfactant components.

The dynamic surface pressure-area properties of pure and binary mixed films of rac-1,2-dipalmitoyl-glycero-3-phosphocholine, 1,2-diocoyl-sn-glycero-3-phosphocholine and cholesterol were investigated at 23 degrees C and 37 degrees C. The pure films and binary mixtures of rac-1,2-dipalmitoyl-glycero-3-phosphocholine: 1,2-dioeoyl-sn-glycero-3-phosphocholine and rac-1,2-dipalmitoyl-glycero-3-phosphocholine:cholesterol were characterized both for dilute surface initial concentrations of 150 Angstrom 2/molecule and for surface excess initial values of 15-50 Angstrom 2/molecule. The results show that the addition of 1,2-dioeoyl-sn-glycero-3-phosphocholine or cholesterol in a binary film with rac-1,2 dipalmitoyl-glycero-3-phosphocholine acts to improve the surface reentry and respreading properties over those of pure rac-1,2-dipalmitoyl-glycero-3-phosphocholine films upon dynamic compression past collapse. This effect is even more pronounced at 37 degrees C than at 23 degrees C, as demonstrated by the application of a collapse plateau ratio criterion. The enhanced dynamic respreading correlates with the effect of 1,2-dioleoyl-sn-glycero-3-phosphocholine and cholesterol in decreasing the gel to liquid crystal transition temperature of rac-1,2-dipalmitoyl-glycero-3-phosphocholine water dispersons, as well as with their facilitation of post-collapse dynamic surface pressure relaxation in binary films with rac-1,2-dipalmitoyl-glycero-3-phosphocholine.