Samuel Schürch

Surface tension at low lung volumes: Dependence on time and alveolar size

We measured surface tension in individual alveoli by observing the spreading properties of fluid droplets placed by micropipette on the alveolar surfaces. The test fluids were calibrated on monolayers of dipalmitoyl phosphatidylcholine spread at the air-saline interface of a captive bubble. The air bubble was floated by buoyancy against a ceiling of 0.5% agar. The bubble surface tension could be altered by inflating or deflating the bubble, and the value of the surface tension was determined by shape analysis for the sessile drop. Test fluid droplets were placed by micropipette onto the upper, flat bubble surface and the diameters of these droplets were measured with a microscope. In cat lungs held at 40% total lung capacity and 37 degrees C the surface tension remained below 1 mN . m -1 for about 10 min, and then increased slowly in a linear fashion to 9 mN . m -1 in 70 min. During stepwise deflation from 70% to 40% total lung capacity the surface tension changed from approximately 10 mN . m -1 to less than 1 mN . m -1. At each step during deflation we compared surface tension in alveoli of differing size and location. At any given lung volume in the range between 70% and 40% total lung capacity we found equal values for the alveolar surface tension regardless of alveolar size and location.

Alveolar surface tensions in excised rabbit lungs: Effect of temperature

In excised, perfused rabbit lungs the alveolar surface tension was measured in individual alveoli over the entire P-V loop at different temperatures (22 and 37 degrees C), using an improved microdroplet method. Additional in vitro experiments are reassuring that the microdroplets do not affect the properties of the alveolar surface film. The in situ measurements show that the alveolar surface tension and the surface tension to volume relation are essentially the same at 22 and 37 degrees C. A maximal surface tension of about 30 mN X m-1 was measured at TLC, and there is a substantial surface tension to volume hysteresis, which amounts to almost 10 mN X m-1 in the middle volume range of a complete pressure volume cycle of the lung. However, with respect to the absolute values of alveolar surface tension, and the shape and width of the hysteresis, these directly obtained results are different from previous findings.

Determination of cell/medium interfacial tensions from contact angles in aqueous polymer systems

The contact angles on cell layers of a series of polymeric droplets from aqueous two-phase systems of dextran and poly(ethylene glycol) have been used to determine the critical or limiting interfacial tension for spreading on the cell layers. Test droplets of the denser dextran-rich phase were formed in the lighter poly(ethylene glycol)-rich phase. The interfacial tensions, gamma, between the phases were determined with the pendant drop method, and a linear relationship was found between gamma-1/2 and the cosine of the angle the droplets made with the cell layers (Good-Girifalco plot). We were thus able to determine the limiting or critical interfacial tension, gamma c, for spreading on the cell layers. The value of gamma c is a measure of the interfacial energy of the cell/bathing medium interface. Values of gamma c obtained by this method include the following: 0.65 and 0.84 microN . m-1 for human erythrocytes and neutrophils, respectively; 0.93 microN . m-1 for porcine pulmonary macrophages; 0.75--3.60 microM . m-1 for various transformed murine lymphoid cell lines, and 2.53 microN . m-1 for Balb/c murine spleen lymphocytes. Exposure to various agents has differing effects on gamma c. Concanavalin A reduces gamma c, and bacterial lipopolysaccharide increases gamma c of murine spleen lymphocytes. The calcium ionophore, A23187, increases gamma c of both porcine pulmonary macrophages and murine spleen lymphocytes. This new method provides a quantitative approach to the cell surface energy and hydrophobicity which are thought to play an important role in membrane-mediated phenomena and in cell adhesion.

Interfacial tensions at lipid—water interfaces. comparison of equation-of-state predictions with direct experimental measurements

Studies of interfacial tensions in solid/liquid/vapor systems usually take as their starting point the equation derived by Young in 1805. However, both the derivation and the application of the equation of state have so far been limited to solid/liquid/vapor interfaces in 2-component, 3-phase systems. There are a number of solid/liquid/liquid systems where determination of vapor/solid interfaces would be of considerable interest. There appears to be no intuitive objection to the applicability of the equation of state at such interfaces, but it is possible, for example, that entropic effects at an oil-water interface could introduce errors which play little role at the more well-behaved solid/vapor interface. Accordingly, the application of the equation of state at lipid/water/oil interface has been investigated where interfacial tensions may be measured directly from deformation measurements and compared with indirect estimates from contact angle data and the equation of state. 10 references.

Interference of bronchographic agents with lung surfactant.

Dionosil Oily (a suspension of propyliodone crystals in peanut oil and powdered tantalum were introduced into the right principal bronchi of rabbit lungs. The left lungs were used as controls. Pressure-volume characteristics of excised lungs with Dionosil Oily or peanut oil demonstrated significantly reduced compliance on inflation at a pressure of 3-4 cm H2O. These lungs also retained less air on deflation and therefore demonstrated a significantly reduced stability index. Histological sections revealed microatelectasis closely associated with crystals and/or peanut oil. Lungs with tantalum powder were not measurably influenced by the bronchographic agents. Surface balance experiments with lung surfactant and synthetic dipalmitoyl phosphatidylcholine (DPPC) demonstrated an increased minimum surface tension due to the oil suspension of propyliodone, peanut oil and particles (propyliodone and tantalum). There is good evidence that the oil suspension of propyliodone reduced the surface activity of lung surfactant in situ. Particles also may prevent the minimum surface tension from reaching relatively low values if they enter the alveoli in sufficient quantities.

A synthetic emulsion reproduces the functional properties of pulmonary surfactant

An effective substitute for pulmonary surfactant must be able to reduce water-vapour surface tensions to under 1 mN/m and it must spread rapidly and spontaneously at the air interface from the aqueous phase. Pure dipalmitoylphosphatidylcholine meets the former requirement, but not the latter. A synthetic surfactant is described which meets both of these criteria. The surfactant is prepared as a DPPC monolayer stabilizing an aqueous emulsion of an inert fluorocarbon oil; it spreads rapidly at the air/liquid interface, lowers the surface tension to under 1 mN/m during compression at the air/liquid interface and restores normal pressure-volume characteristics to surfactant-depleted lungs.

Membrane glycoprotein and surface free energy changes in hypoxic fibroblast cells

Hypoxia affects the biochemistry of mammalian cells and thus alters their sensitivity to subsequent chemo- and radiotherapy. When V79 Chinese hamster lung fibroblasts were grown under conditions of extreme hypoxia (less than 10 ppm O2) there was a significant shift in the membrane glycoprotein composition. Scanning electron microscopy revealed altered cell surface morphology including loss of pseudopodial projections. Experiments to determine changes in interfacial free energy of these cells using equilibrium two phase systems of poly(ethylene glycol) (PEG) and dextran were carried out. Test fluid droplets of the denser dextran-rich phase were formed on layers of cells in the PEG-rich phase as the bathing medium, and the contact angles the droplets made with the cell layers were measured from photomicrographs. The contact angles on cells in the plateau phase increased significantly with time of exposure to hypoxia, from 25 degrees (zero time) to 35 degrees (6 h) to 60 degrees (9 h). Contact angles on cells in the exponential phase increased from 80 degrees (zero time) to 150 degrees after 20 h of hypoxia. It appears that the altered contact angles reflect changes in cell surface hydrophobicity that may, in part, reflect alterations in the membrane glycoprotein composition.

Differential adhesive properties of the surface of human blood flukes Schistosoma mansoni. Sexual, regional, and developmental differences in interfacial free energies and structure of glycocalyx.

While infecting a vertebrate host, blood flukes (Schistosoma mansoni) must continually resist adhesions by immune effector cells. However, the male and female schistosomes must adhere to one another in order to establish and maintain the sexual pairing process after 4 wk postinfection. Using a contact angle method, the relative adhesiveness of male and female parasites were determined. Results indicate that schistosomes restrict effector cell adhesion through developmental, sexual, and regional differences in adhesive properties.While infecting a vertebrate host, blood flukes (Schistosoma mansoni) must continually resist adhesions by immune effector cells. However, the male and female schistosomes must adhere to one another in order to establish and maintain the sexual pairing process after 4 wk postinfection. Using a contact angle method, the relative adhesiveness of male and female parasites were determined. Results indicate that schistosomes restrict effector cell adhesion through developmental, sexual, and regional differences in adhesive properties.

The effect of leukotrienes on porcine alveolar macrophage function

The ability of the synthetic leukotrienes LTB4, LTC4, LTD4 and LTE4 to stimulate porcine AM was compared with that of two known AM stimuli: zymosan, a particulate stimulus and phorbol myristate acetate (PMA), a soluble stimulus. The criteria for AM stimulation were: increased generation of superoxide anion (O2-), the release of the lysosomal enzymes N-acetyl-beta-D-glucosaminidase (NABG) and arylsulfatase and an increase in surface free energy. Whereas zymosan and PMA both stimulated AM according to each of the three criteria, the effect of leukotrienes was relatively minor. LTB4 (10(-6) M) and LTD4 (10(-6) M) caused a modest reduction in spontaneous O2- release by AM. LTD4 (10(-6) M) also caused a small (18%), but significant (p less than 0.05), reduction in the additional O2- release induced by PMA. LTC4 and LTE4 did not alter spontaneous O2- release. Neither spontaneous nor stimulated enzyme release was systematically altered by any of the leukotrienes. LTD4 caused a cysteine-inhibitable, dose-dependent increase in surface free energy with a plateau at concentrations above 10(-8) M. The increased surface free energy induced by LTD4 may be a consequence of binding to a surface dipeptidase.

Rabbit bladder-surface mucin: A thermodynamic mechanism for inhibiting bacterial adhesion

SummaryA possible thermodynamic mechanism for the inhibition of bacterial adhesion to the epithelial bladder surface was investigated in rabbits. Contact angles of aqueous polymeric droplets were measured to assess the relative hydration and surface-free energy, of normal and mucinfree bladder surfaces. We measured an angle of 91.2±1.2° (SEM), n=37 for the intact mucin surface and an angle of 120.5±1.2°, n=46 for the epithelium after the mucin was removed with acid. These results indicate that mucin makes the epithelial surface significantly more hydrophilic and so produces a very low free energy interface with the urine environment. Such a low energy surface would inhibit bacterial adhesion because the surface already exists at its free energy minimum.