Effect of the hydrophobic surfactant proteins on the surface activity of spread films in the captive bubble surfactometer

The main function of pulmonary surfactant, a mixture of lipids and proteins , is to reduce the surface tension at the air/liquid interface of the lung. The hydrophobic surfactant proteins SP-B and SP-C are required for this pr ocess. When testing their activity in spread films in a captive bubble surf actometer, both SP-B and SP-C showed concentration dependence for lipid ins ertion as well as for lipid film refinement. Higher activity in DPPC refine ment of the monolayer was observed for SP-B compared with SP-C. Further dif ferences between both proteins were found, when subphase phospholipid vesic les, able to create a monolayer-attached lipid reservoir, were omitted. SP- C containing monolayers showed gradually increasing minimum surface tension s upon cycling, indicating that a lipid reservoir is required to prevent lo ss of material from the monolayer. Despite reversible cycling dynamics, SP- B containing monolayers failed to reach near-zero minimum surface tensions, indicating that the reservoir is required for stable films. (C) 2000 Elsev ier Science Ireland Ltd. All rights reserved.