Dynamic surface properties of phosphatidylglycerol-dipalmitoylphosphatidylcholine mixed films

Abstract

This paper studies the dynamic surface pressure-area (π-A) behavior of phosphatidylglycerol (PG) with a mixed fatty acid distribution (bacterial) in pure and binary mixed films with dipalmitoyl phosphatidylcholine (DPL). At 23°C, bacterial PG films generate maximum dynamic surface pressures of only 48–49 dyn/cm on a 0.15 M sodium chloride subphase for both dilute and surface excess initial conditions. By contrast, binary mixed films of 90:10 DPL/PG reach maximum π values of the order of 70 dyn/cm at similar conditions, the same as for pure DPL films. A collapse plateau ratio criterion is used to show that respreading after dynamic compression past film collapse is enhanced in 90:10 DPL/PG films as compared to pure DPL for a dilute surface initial condition, but not for the surface excess condition, at room temperature. Respreading in pure bacterial PG films is also slightly improved over corresponding pure DPL films for some initial conditions at 23°C, but the magnitude of this effect is not as large as might be expected from the significant unsaturated and cyclopropane fatty acid percentage present in bacterial PG. Differential Scanning Calorimetry (DSC) measurements on DPL/PG mixtures show decreasing T c with peak broadening as the percentage of bacterial PG is increased. The experiments here do not establish a clearly required functional role for 10% PG in pulmonary surfactant surface behavior. Further surface studies are suggested before long-term clinical trials of PG containing mixtures for exogenous replacement therapy in Neonatal Respiratory Distress Syndrome (RDS) are initiated on a widespread basis.