Menthol-induced action potentials in Conocephalum conicum as a result of unspecific interactions between menthol and the lipid phase of the plasma membrane.

Our previous study has shown that the liverwort Conocephalum conicum generates action potentials (APs) in response to both temperature drop and menthol, which are also activators of the TRPM8 (transient receptor potential melastatin 8) receptor in animals. Not only similarities but also differences between electrical reactions to menthol and cooling observed in the liverwort aroused our interest in the action of menthol at the molecular level. Patch-clamp investigations have shown that menthol causes a reduction of current flowing through slow vacuolar (SV) channels to 29 ± 10% of the initial value (n = 9); simultaneously, it does not influence magnitudes of currents passing through a single SV channel. This may point to an unspecific interaction between menthol and the lipid phase of the membrane. An influence of menthol on lipid organization in membranes was investigated in two-component monomolecular layers formed with menthol and dipalmitoylphosphatidylcholine (DPPC) at the argon-water interface. Analyses of the mean molecular area parameters vs the molar fraction of the menthol component have shown over-additivity (approximately 20 Å(2) ) in the region of high molar fractions of menthol. Infrared absorption spectroscopy studies have shown that menthol, most probably, induces breaking of a hydrogen bond network formed by ester carbonyl groups and water bridges in the lipid membrane and binds to the polar head group region of DPPC. We conclude that the disruption in the lipid phase of the membrane influences ion channels and/or pumps and subsequently causes generation of APs in excitable plants such as C. conicum.

The melting of pulmonary surfactant monolayers.

Monomolecular films of phospholipids in the liquid-expanded (LE) phase after supercompression to high surface pressures (pi), well above the equilibrium surface pressure (pi(e)) at which fluid films collapse from the interface to form a three-dimensional bulk phase, and in the tilted-condensed (TC) phase both replicate the resistance to collapse that is characteristic of alveolar films in the lungs. To provide the basis for determining which film is present in the alveolus, we measured the melting characteristics of monolayers containing TC dipalmitoyl phosphatidylcholine (DPPC), as well as supercompressed 1-palmitoyl-2-oleoyl phosphatidylcholine and calf lung surfactant extract (CLSE). Films generated by appropriate manipulations on a captive bubble were heated from < or =27 degrees C to > or =60 degrees C at different constant pi above pi(e). DPPC showed the abrupt expansion expected for the TC-LE phase transition, followed by the contraction produced by collapse. Supercompressed CLSE showed no evidence of the TC-LE expansion, arguing that supercompression did not simply convert the mixed lipid film to TC DPPC. For both DPPC and CLSE, the melting point, taken as the temperature at which collapse began, increased at higher pi, in contrast to 1-palmitoyl-2-oleoyl phosphatidylcholine, for which higher pi produced collapse at lower temperatures. For pi between 50 and 65 mN/m, DPPC melted at 48-55 degrees C, well above the main transition for bilayers at 41 degrees C. At each pi, CLSE melted at temperatures >10 degrees C lower. The distinct melting points for TC DPPC and supercompressed CLSE provide the basis by which the nature of the alveolar film might be determined from the temperature-dependence of pulmonary mechanics.

Lung surfactant dysfunction in tuberculosis: effect of mycobacterial tubercular lipids on dipalmitoylphosphatidylcholine surface activity.

In pulmonary tuberculosis, Mycobacterium tuberculosis bacteria reside in the alveoli and are in close proximity with the alveolar surfactant. Mycolic acid in its free form and as cord factor, constitute the major lipids of the mycobacterial cell wall. They can detach from the bacteria easily and are known to be moderately surface active. We hypothesize that these surface-active mycobacterial cell wall lipids could interact with the pulmonary surfactant and result in lung surfactant dysfunction. In this study, the major phospholipid of the lung surfactant, dipalmitoylphosphatidylcholine (DPPC) and binary mixtures of DPPC:phosphatidylglycerol (PG) in 9:1 and 7:3 ratios were modelled as lung surfactant monolayers and the inhibitory potential of mycolic acid and cord factor on the surface activity of DPPC and DPPC:PG mixtures was evaluated using Langmuir monolayers. The mycobacterial lipids caused common profile changes in all the isotherms: increase in minimum surface tension, compressibility and percentage area change required for change in surface tension from 30 to 10 mN/m. Higher minimum surface tension values were achieved in the presence of mycolic acid (18.2+/-0.7 mN/m) and cord factor (13.28+/-1.2 mN/m) as compared to 0 mN/m, achieved by pure DPPC film. Similarly higher values of compressibility (0.375+/-0.005 m/mN for mycolic acid:DPPC and 0.197+/-0.003 m/mN for cord factor:DPPC monolayers) were obtained in presence of mycolic acid and cord factor. Thus, mycolic acid and cord factor were said to be inhibitory towards lung surfactant phospholipids. Higher surface tension and compressibility values in presence of tubercular lipids are suggestive of an unstable and fluid surfactant film, which will fail to achieve low surface tensions and can contribute to alveolar collapse in patients suffering from pulmonary tuberculosis. In conclusion a biophysical inhibition of lung surfactant may play a role in the pathogenesis of tuberculosis and may serve as a target for the development of new drug loaded surfactants for this condition.

Dipalmitoylphosphatidylcholine is not the major surfactant phospholipid species in all mammals.

Pulmonary surfactant, a complex mixture of lipids and proteins, lowers the surface tension in terminal air spaces and is crucial for lung function. Within an animal species, surfactant composition can be influenced by development, disease, respiratory rate, and/or body temperature. Here, we analyzed the composition of surfactant in three heterothermic mammals (dunnart, bat, squirrel), displaying different torpor patterns, to determine: 1) whether increases in surfactant cholesterol (Chol) and phospholipid (PL) saturation occur during long-term torpor in squirrels, as in bats and dunnarts; 2) whether surfactant proteins change during torpor; and 3) whether PL molecular species (molsp) composition is altered. In addition, we analyzed the molsp composition of a further nine mammals (including placental/marsupial and hetero-/homeothermic contrasts) to determine whether phylogeny or thermal behavior determines molsp composition in mammals. We discovered that like bats and dunnarts, surfactant Chol increases during torpor in squirrels. However, changes in PL saturation during torpor may not be universal. Torpor was accompanied by a decrease in surfactant protein A in dunnarts and squirrels, but not in bats, whereas surfactant protein B did not change in any species. Phosphatidylcholine (PC)16:0/16:0 is highly variable between mammals and is not the major PL in the wombat, dunnart, shrew, or Tasmanian devil. An inverse relationship exists between PC16:0/16:0 and two of the major fluidizing components, PC16:0/16:1 and PC16:0/14:0. The PL molsp profile of an animal species is not determined by phylogeny or thermal behavior. We conclude that there is no single PL molsp composition that functions optimally in all mammals; rather, surfactant from each animal is unique and tailored to the biology of that animal.

Rheological behavior and parameters of the in vitro model of lung surfactant systems: the role of the main phospholipid component.

The proposed in vitro model for studying the alveolar surface layer of the lungs enables one to investigate the surface intermolecular forces which influence the stability of the alveolus. The general role for the stability of the alveolus belongs to the phospholipids in the alveolar surfactant and predominantly to their main component dipalmitoylphosphatidylcholine (DPPC). The aim of the study was to investigate the rheological behavior of DPPC and exogenous surfactant preparations used in neonatal clinical practice. Data for the rheological behavior of the solutions of the commercially available surfactants, Infasurf, Exosurf and Survanta, as well as of DPPC (their main phospholipid component) at shear rates from 0.024 to 94.5 s(-1) under steady and transient flow conditions at 23 degrees C were obtained. Infasurf and Exosurf showed Newtonian rheological behavior, while Survanta revealed the shear-thinning behavior of a non-Newtonian pseudoplastic fluid. The rheological properties of aqueous solutions of DPPC containing 0.14 M NaCl at concentrations from 100 and 630 microg/ml of phospholipid (chosen from the dependence of the probability for bilayer film formation) were studied. Differences observed in the rheological properties of the exogenous surfactants were interpreted on the basis of their composition, the presence of other phospholipid components, certain additives and surfactant proteins, as well as the bulk structures formed from them. The relevance of the results for the delivery of exogenous surfactants and their spreading in replacement therapy is discussed.

Regulation of platelet-activating factor synthesis in human monocytes by dipalmitoyl phosphatidylcholine.

Platelet-activating factor (PAF) has a major role in inflammatory responses within the lung. This study investigates the effect of pulmonary surfactant on the synthesis of PAF in human monocytic cells. The pulmonary surfactant preparation Curosurf significantly inhibited lipopolysaccharide (LPS)-stimulated PAF biosynthesis (P<0.01) in a human monocytic cell line, Mono mac-6 (MM6), as determined by (3)H PAF scintillation-proximity assay. The inhibitory properties of surfactant were determined to be associated, at least in part, with the 1,2-dipalmitoyl phosphatidylcholine (DPPC) component of surfactant. DPPC alone also inhibited LPS-stimulated PAF biosynthesis in human peripheral blood monocytes. DPPC treatment did not affect LPS-stimulated phospholipase A(2) activity in MM6 cell lysates. However, DPPC significantly inhibited LPS-stimulated coenzyme A (CoA)-independent transacylase and acetyl CoA:lyso-PAF acetyltransferase activity. DPPC treatment of MM6 cells decreased plasma membrane fluidity as demonstrated by electron paramagnetic resonance spectroscopy coupled with spin labeling. Taken together, these findings indicate that pulmonary surfactant, particularly the DPPC component, can inhibit LPS-stimulated PAF production via perturbation of the cell membrane, which inhibits the activity of specific membrane-associated enzymes involved in PAF biosynthesis.

Discrepancy between phase behavior of lung surfactant phospholipids and the classical model of surfactant function.

The studies reported here used fluorescence microscopy and Brewster angle microscopy to test the classical model of how pulmonary surfactant forms films that are metastable at high surface pressures in the lungs. The model predicts that the functional film is liquid-condensed (LC) and greatly enriched in dipalmitoyl phosphatidylcholine (DPPC). Both microscopic methods show that, in monolayers containing the complete set of phospholipids from calf surfactant, an expanded phase persists in coexistence with condensed domains at surface pressures approaching 70 mN/m. Constituents collapsed from the interface above 45 mN/m, but the relative area of the two phases changed little, and the LC phase never occupied more than 30% of the interface. Calculations based on these findings and on isotherms obtained on the continuous interface of a captive bubble estimated that collapse of other constituents increased the mol fraction of DPPC to no higher than 0.37. We conclude that monolayers containing the complete set of phospholipids achieve high surface pressures without forming a homogeneous LC film and with a mixed composition that falls far short of the nearly pure DPPC predicted previously. These findings contradict the classical model.

Structure-selective anesthetic action of steroids: anesthetic potency and effects on lipid and protein.

Alphaxalone was a clinically used steroid anesthetic. Its analog delta 16-alphaxalone is nonanesthetic. The only difference between the two is the presence of a double bond at the hydrophobic end of the delta 16-alphaxalone molecule. This study determined the anesthetic potency of alphaxalone and delta 16-alphaxalone in goldfish and compared it with their effects on dipalmitoylphosphatidylcholine (DPPC) membranes and an alpha-helix polypeptide, poly(L-lysine). The goldfish EC50 values were: alphaxalone 5 mumol/L and delta 16-alphaxalone 80 mumol/L. Because these steroids are insoluble to water, the bulk of the steroid in water is absorbed by the fish. Larger containers hold more steroids than smaller containers at the same steroid concentrations. Then, EC50 values vary according to the size of the container. By assuming that the total amount of steroids in the container is distributed into the fish, the EC50 values expressed by the concentration in the fish body become 1.9 mmol/L for alphaxalone, and 30.5 mmol/L for delta 16-alphaxalone. A monoamino acid peptide, poly(L-lysine), can be formed into random-coil, alpha-helix, or beta-sheet. Addition of 0.07 mmol/L alphaxalone to the alpha-helix poly(L-lysine) partially transformed it to a beta-sheet structure. An equivalent change was observed with 3.0 mmol/L delta 16-alphaxalone. These values translate into 3.5 mmol/L for alphaxalone and 0.15 mol/L for delta 16-alphaxalone, when expressed by the concentration in the peptide. The change from alpha-helix to beta-sheet is accompanied by dehydration of the surface of poly(L-lysine). The steroids decreased the phase-transition temperature of DPPC membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of anaesthetics on the dynamic heterogeneity of lipid membranes.

The influence of membrane-perturbing drugs such as anaesthetics on the lipid membrane properties is analyzed theoretically on the basis of a general microscopic interaction model of the gel-to-fluid chain melting transition of one-component phospholipid membranes and phospholipid membranes with a low content of cholesterol. Monte Carlo computer simulation of the model shows that the gel-to-fluid transition of the lipid membrane, manifested in the formation of dynamically coexisting domains of gel and fluid lipids, is strongly influenced by the presence of anaesthetics. Macroscopically the effect of anaesthetics on the membrane properties is seen in a depression of the transition temperature and a smearing of thermodynamic response functions like the specific heat. Microscopically the calculations reveal that anaesthetics have a high affinity to the fluctuating domain interfaces that are dominated by kink-like lipid-chain conformations. This leads to formation of more interfaces and to a locally high concentration of anaesthetics in the interfacial regions, which is much larger than the global concentration in the membrane. Important membrane components like cholesterol, which also has been shown to be interfacially active, are found to decrease the absorption of anaesthetics and to squeeze out anaesthetics from the interfaces. The results of the general model study of anaesthetics-membrane interactions are discussed in relation to both general anaesthetics, like halothane, and local anaesthetics like cocaine-derivatives.

FTIR evidence for alcohol binding and dehydration in phospholipid and ganglioside micelles.

We theorize that intoxicants and modern anesthetics bind at the membrane-water interface and displace (dehydrate) bound water molecules by breaking the hydrogen bonds. We tested this hypothesis by examining the effect of butanol on the binding of water to the polar regions of lipids in reversed micelles. Understanding the mechanisms of intoxication requires studies in physiologically relevant systems such as systems containing sialoglycoconjugates, especially gangliosides, which concentrate in the synapses of neural tissue. Therefore, we compared butanol effects on phospholipid with effects on ganglioside. Hydrogen-bond breaking activity of 1-butanol was studied in reversed micelles made of dipalmitoylphosphotidylcholine (DPPC), ganglioside (GM1 and GT1b) or the lipid mixture in a D2O-CCl4 medium. Fourier transform infrared spectroscopy (FTIR) data indicated that 1-butanol binds to DPPC and to gangliosides. Adding GM1 to the DPPC micelles introduces a new binding site for the alcohol. GT1b binds more butanol than GM1, because of more binding sites provided by extra sialic acid moieties. Spectral red shifts indicate that both water and butanol bind to the C = O group of sialic acid. Butanol partially releases the surface-bound water by disrupting hydrogen bonds, as indicated by an appearance of a sharp new free OD stretching band of the released D2O molecules. However, control studies with lipid-free systems in CCl4 revealed that a free OD peak could occur from a deuterium exchange reaction between D2O and 1-butanol(ol-h).(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary surfactant secretion is regulated by the physical state of extracellular phosphatidylcholine.

Pulmonary alveolar type II cells synthesize, secrete, and recycle the components of pulmonary surfactant. In this report we present evidence that dipalmitoylphosphatidylcholine is a potent inhibitor of surfactant lipid secretion by type II cells. Monoenoic and dienoic phosphatidylcholines with fatty acids of 16 or 18 carbons are ineffective as inhibitors of surfactant lipid secretion. In contrast, disaturated phosphatidylcholines, with either symmetric or asymmetric pairs of fatty acids of 14, 16, or 18 carbons, exhibit inhibition of surfactant secretion that correlates extremely well with the phase transition temperature (Tc) of the phospholipid. The inhibitory activity of dipalmitoylphosphatidylcholine is not dependent upon lipid stereochemistry. N-Methylated derivatives of dipalmitoylphosphatidylethanolamine are significantly less effective than phosphatidylcholine as inhibitors. Phosphatidylcholines below their phase transition temperature are inhibitors of surfactant secretion, whereas those above their phase transition temperature are either ineffective or weakly inhibitory. The phase transition dependence of inhibition is observed when type II cells are incubated at 37 degrees C with different species of phosphatidylcholine. In addition, if type II cells are stimulated to secrete at different temperatures the efficacy of a given phospholipid as an inhibitor is dependent on its relationship to Tc (i.e. dipalmitoylphosphatidylcholine with a Tc of 41 degrees C significantly inhibits secretion at 37 degrees C but not at 42 degrees C). Inhibition of surfactant secretion by dipalmitoylphosphatidylcholine is abrogated when it is incorporated into the same liposome with dioleoylphosphatidylcholine as a 50:50 mixture. In contrast, the simultaneous addition of two separate populations of liposomes, one composed of dipalmitoylphosphatidylcholine and the other composed of dioleoylphosphatidylcholine, does not significantly alter the inhibitory activity found with dipalmitoylphosphatidylcholine alone. These data provide compelling evidence that the physical state of phosphatidylcholine can regulate surfactant secretion from alveolar type II cells and suggest a unique mechanism for regulating exocytosis in the alveolus of the lung.

Gastric mucosal barrier: barrier to hydrogen ions imparted by gastric surfactant in vitro.

A simple experiment is described which shows how the highly surface active ingredient of gastric surfactant (DPPC) can be deposited on a filter paper to reduce the rate of transmission of hydrogen ions by one to two orders of magnitude. This finding is compatible with previous studies implying that the hydrophobic layer of surface active phospholipid provides the gastric mucosal barrier as a distinct physical entity.

Comparisons of lipid dynamics and packing in fully interdigitated monoarachidoylphosphatidylcholine and non-interdigitated dipalmitoylphosphatidylcholine bilayers: cross polarization/magic angle spinning 13C-NMR studies.

13C-NMR spectra have been obtained at 50.3 MHz for monoarachidoylphosphatidylcholine (MAPC) and dipalmitoylphosphatidylcholine (DPPC) dispersions from 25 degrees C to 55 degrees C and for DPPC polycrystals at 25 degrees C using the cross polarization/magic angle spinning technique. Differential scanning calorimetric studies on DPPC and MAPC dispersions show comparable lipid phase transitions with transition temperatures at 41 degrees C and 45 degrees C, respectively, and thus enable the comparison of thermal, structural and dynamic differences between these two systems at corresponding temperatures. Conformational-dependent 13C chemical shift studies on DPPC dispersions demonstrate not only the coexistence of the tilted gel (L beta') and liquid-crystalline (L alpha) phases in the rippled gel (P beta') phase, but also the presence of an intermediate third microscopic phase as evidenced by three resolvable peaks for omega - 1 methylene carbon signals at the temperature interval between Tp and Tm. By comparing chemical shifts of MAPC in the hydrocarbon chain region with those of DPPC at similar reduced temperatures, it can be concluded that the packings are perturbed markedly in the middle segment of the fatty acyl chain during the lamellar to micellar transition. However, terminal methylene and methyl groups of interdigitated MAPC lamellae were found to be more ordered than those of non-interdigitated DPPC bilayers in the gel state. Interestingly, the terminal methyl groups of MAPC in the micelles remain to be relatively ordered; in fact, they are more ordered than the corresponding acyl chain end of DPPC in the liquid-crystalline state. Analysis of data obtained from rotating frame proton spin-lattice relaxation measurements shows a highly mobile phosphocholine headgroup, a rigid carbonyl group and an ordered hydrocarbon chain for lamellar MAPC in the interdigitated state. Furthermore, results suggest that free rotations of the glycerol C2-C3 bond within MAPC molecules may occur in the interdigitated bilayer, whereas intramolecular exchange between two conformations of the glycerol backbone in DPPC become possible at temperatures close to the pretransition temperature. Without isotope enrichment, we conclude that high-resolution solid-state 13C-NMR is indeed a useful technique which can be employed to study the packing and dynamics of phospholipids.

Oligolamellar lubrication of joints by surface active phospholipid.

Six studies have been undertaken to test the hypothesis that oligolamellar phospholipid adsorbed to the articular surface contributes to joint lubrication. Synovial fluid (SF) proved highly surface active, rapidly depositing phosphatidylcholine (DPPC) on glass surfaces, rendering them hydrophobic--a property of well rinsed articular surface removable by the same fat solvents known to increase joint friction by 150%. Electron microscope studies demonstrated lamellar bodies (surface active DPPC) on the articular surface and in SF and lamellated phospholipid in light scrapings of joint surfaces. These were consistent with the quantity of phospholipid recovered by solvent rinsing. Friction measurements in vitro demonstrated excellent boundary lubrication imparted by multimolecular layers of DPPC under high load with coefficients of kinetic friction reaching physiological ranges (0.002-0.005).

Mixtures of low molecular weight surfactant proteins and dipalmitoyl phosphatidylcholine duplicate effects of pulmonary surfactant in vitro and in vivo.

Pulmonary surfactant proteins SP-B and SP-C were isolated from lavage fluids of bovine lungs and recombined (lipid/proteins, 9/1, wt/wt) with dipalmitoyl phosphatidylcholine for testing in vitro and in surfactant-deficient adult rats. Using a pulsating bubble surfactometer, we found that inflation pressures of bubbles at minimum radii in these mixtures were 0.34 +/- 0.05 cm H2O (+/- SD, n = 24) after 1 min. These values were not affected by increasing amounts of surfactant protein relative to dipalmitoyl phosphatidylcholine (DPPC). Minimum inflation pressures were similar to those of modified bovine surfactant, surfactant Tokyo Akita (TA) (0.33 +/- 0.05 cm H2O, n = 7). In vivo testing was carried out in adult rats made surfactant deficient by repeated lavage and ventilated with 100% oxygen. Rats received tracheal instillations of either air, DPPC, DPPC/SP-B,C (9:1), or surfactant TA at 50 mg/kg body weight. Surfactant TA and DPPC/SP-B, SP-C mixtures resulted in similar immediate and sustained improvements in arterial oxygenation (308 +/- 66 torr, n = 10 and 312 +/- 101 torr, n = 6 at 30 min posttreatment) that were significantly greater than those of sham (76 +/- 24 torr, n = 17) and DPPC-treated rats (64 +/- 32 torr, n = 7). Rats treated with either DPPC/SP-B,C mixtures or surfactant TA showed similar postmortem static lung compliances (2.3 +/- 0.8 ml/cm H2O/kg, n = 8 and 1.9 +/- 0.4 ml/cm H2O/kg, n = 5, respectively) that were significantly larger than sham (1.3 +/- 0.3 ml/cm H2O/kg, n = 14) and DPPC-treated rats (1.2 +/- 0.2 ml/cm H2O/kg, n = 6).(ABSTRACT TRUNCATED AT 250 WORDS)

A differential scanning calorimetry study of the interaction of alpha-tocopherol with mixtures of phospholipids.

When alpha-tocopherol was included in multibilayer vesicles of dimyristoylphosphatidylcholine, dipalmitoylphosphatidylcholine and distearoylphosphatidylcholine it induced a broadening of the main transition and a displacement of this transition to lower temperatures, as seen by differential scanning calorimetry. This effect was quantitatively more important in the samples of distearoylphosphatidylcholine than in those of the other phosphatidylcholines. Alpha-Tocopherol when present in equimolar mixtures of dimyristoylphosphatidylcholine and diastearoylphosphatidylcholine, which show monotectic behaviour, preferentially partitions in the most fluid phase. The effect of alpha-tocopherol on the phase transition of dilauroylphosphatidylethanolamine and dipalmitoylphosphatidylethanolamine is qualitatively different of that observed on phosphatidylcholines, and several peaks are observed in the calorimetric profile, probably indicating the formation of separated phases with different contents in alpha-tocopherol. The effect was more apparent in dipalmitoylphosphatidylethanolamine than in dilauroylphosphatidylethanolamine. The inclusion of alpha-tocopherol in equimolar mixtures of dilauroylphosphatidylethanolamine and dipalmitoylphosphatidylcholine, which show cocrystallization, only produced a broadening of the phase transition and a shift to lower temperatures. However, in the case of equimolar mixtures of dipalmitoylphosphatidylcholine which also show cocrystallization, the effect was to cause lateral phase separation with the formation of different mixtures of phospholipids and alpha-tocopherol. Alpha-Tocopherol was also included in equimolar mixtures of phosphatidylethanolamine and phosphatidylcholine showing monotectic behaviour, and in this case alpha-tocopherol preferentially partitioned in the most fluid phase, independently of whether this was composed mainly of phosphatidylcholine or of phosphatidylethanolamine.

The role of the low-molecular weight (less than or equal to 15,000 daltons) apoproteins of pulmonary surfactant.

An artificial surfactant was prepared by combining synthetic dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylglycerol and the low-molecular weight (less than or equal to 15,000 daltons) surfactant apoproteins in the proportions 80:20:5. In the Wilhelmy balance, this surfactant formed a film with an equilibrium surface tension of 29 mN/m; surface tension was reduced to nearly zero during cyclic film compression, with effective respreadability during multiple compression-expansion cycles; similar surface properties were recorded with a pulsating bubble. When instilled into the airways of artificially ventilated immature newborn rabbits, the apoprotein-based artificial surfactant produced a five-fold increase in tidal volumes at insufflation pressure 25 cm H2O; this effect is similar to that obtained in previous experiments with natural surfactant phospholipids, administered in equal concentration (5 mg/ml). Higher concentration of the apoprotein-based surfactant could not be evaluated in vivo due to the high viscosity of the material. Systematic studies should be undertaken to find out whether an even more effective artificial surfactant could be prepared from the low-molecular weight apoproteins and other combinations of synthetic phospholipids.