Effect of serum albumin on dynamic force-area curve of dipalmitoyl lecithin

In line with previous findings at 25 degrees C, solutions of serum albumin in the subphase stabilized the surface activity of DPL spread films at 25 degrees C as well as 37 degrees C. In contrast, films adsorbed from mixtures of DPL and albumin exhibitied a marked inhibitory action of the albumin on DPL activity. The inhibitory effect increased with the relative protein concentration but, with albumin/DPL ratios smaller than 2, the DPL activity was regained gradually with cycling. With larger albumin/DPE negative effect of albumin was counteracted by higher temperatures (37 degrees C vs 25 degress C) and modest cholesterol concentrations; with greater cholesterol concentrations the known inhibitory effect of cholesterol prevailed. The inhibitory effect of albumin was potentiated by humidity; saturation of the atmosphere with water vapor at 37 degrees C abolished the DPL character of DPL-RSA mixtures and prevented its return (zero surface tension) upon reversal of the atmosphere from saturated water vapor to dry air. The data are important in the interpretation of the surface activity of pulmonary washings and other pulmonary extracts.