The contact angle induced by DPL at pulmonary epithelial surfaces.

A contact angle has been measured at the surface of dog tracheal epithelium by means of two surface balances simultaneously monitoring the apparent surface tension of the same film in a Langmuir trough - one method dependent upon contact angle and the other independent of contact angle. This was confirmed by direct observation. The contact angle was absent for Ringer's solution alone but was induced by DPL deposited on the fluid surface in physiological concentrations. The contact angle varied from 9 degrees to 67 degrees for compression of the DPL film from 100% to 27.5% of its original area and displayed hysteresis with respect to area. These findings show that DPL has unusual surface properties in reducing surface tension yet decreasing wettability, i.e. acting as an anti-wetting agent. The physiological advantages of this unusual combination of properties are discussed in relation to maintaining pulmonary homeostasis and the forward propulsion of mucus which could be facilitated by the differential wettability of cilia induced by DPL. One possible disadvantage of DPL is indicated where fluid plugs might seal an airway - such as in the newborn.