Reversible and irreversible inactivation of preformed pulmonary surfactant surface films by changes in subphase constituents.

Several mechanisms for surfactant inactivation have been reported. In this study, we have measured the reversibility of surfactant inactivation caused by various lipid or protein constituents of plasma or by pH changes. A surfactant of bovine origin was studied in a pulsating surfactometer either when surfactants were premixed with different serum constituents (inactivators) or when inactivators were introduced into subphase fluid surrounding surfactant films formed at an air-liquid interface. Subphase exchanges with sodium bicarbonate or sodium borate raised pH and raised minimal surface tensions either when premixed with surfactant or when introduced with saline subphase beneath a preformed surfactant surface film. The pH effects on surfactant film function were reversible for sodium bicarbonate but not for sodium borate when the subphase with bicarbonate or borate was replaced with saline. Lipids (platelet-activating factor or lysophosphatidylcholine) had non-reversible effects on preformed films. Proteins (fibrinogen or C reactive protein) had reversible effects at low concentrations, but reversibility was less evident at high concentrations. Effects with whole serum were non-reversible at low protein concentrations (0.5 mg/ml). These results add evidence that surfactant inactivation can be caused by multiple mechanisms, both reversible and irreversible.