Phase separation in monolayers of pulmonary surfactant phospholipids at the air-water interface: composition and structure.

The phase behavior of monolayers containing the complete set of purified phospholipids (PPL) obtained from calf surfactant was investigated as a model for understanding the phase transitions that precede compression of pulmonary surfactant to high surface pressure. During compression, both fluorescence microscopy and Brewster angle microscopy (BAM) distinguished domains that separated from the surrounding film. Quantitative analysis of BAM grayscales indicated optical thicknesses for the PPL domains that were similar to the liquid condensed phase for dipalmitoyl phosphatidylcholine (DPPC), the most abundant component of pulmonary surfactant, and higher and less variable with surface pressure than for the surrounding film. BAM also showed the optical anisotropy that indicates long-range orientational order of tilted lipid chains for the domains, but not for the surrounding film. Fluorescence microscopy shows that addition of DPPC to the PPL increased the area of the domains. At fixed surface pressures from 20-40 mN/m, the total area of each phase grew in proportion with the mol fraction of DPPC. This constant variation allowed analysis of the DPPC mol fraction in each phase, construction of a simple phase diagram, and calculation of the molecular area for each phase. Our results indicate that the phase surrounding the domains is more expanded and compressible, and contains reduced amounts of DPPC in addition to the other phospholipids. The domains contain a mol fraction for DPPC of at least 96%.     

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.     

Content-dependent activity of lung surfactant protein B in mixtures with lipids

The content-dependent activity of surfactant protein (SP)-B was studied in mixtures with dipalmitoyl phosphatidylcholine (DPPC), synthetic lipids (SL), and purified phospholipids (PPL) from calf lung surfactant extract (CLSE). At fixed SP-B content, adsorption and dynamic surface tension lowering were ordered as PPL/SP-B approximately SL/SP-B > DPPC/SP-B. All mixtures were similar in having increased surface activity as SP-B content was incrementally raised from 0.05 to 0.75% by weight. SP-B had small but measurable effects on interfacial properties even at very low levels < or =0.1% by weight. PPL/SP-B (0.75%) had the highest adsorption and dynamic surface activity, approaching the behavior of CLSE. All mixtures containing 0.75% SP-B reached minimum surface tensions <1 mN/m in pulsating bubble studies at low phospholipid concentration (1 mg/ml). Mixtures of PPL or SL with SP-B (0.5%) also had minimum surface tensions <1 mN/m at 1 mg/ml, whereas DPPC/SP-B (0.5%) reached <1 mN/m at 2.5 mg/ml. Physiological activity also was strongly dependent on SP-B content. The ability of instilled SL/SP-B mixtures to improve surfactant-deficient pressure-volume mechanics in excised lavaged rat lungs increased as SP-B content was raised from 0.1 to 0.75% by weight. This study emphasizes the crucial functional activity of SP-B in lung surfactants. Significant differences in SP-B content between exogenous surfactants used to treat respiratory disease could be associated with substantial activity variations.     

The role of surfactant proteins in DPPC enrichment of surface films

A pressure-driven captive bubble surfactometer was used to determine the role of surfactant proteins in refinement of the surface film. The advantage of this apparatus is that surface films can be spread at the interface of an air bubble with a different lipid/protein composition than the subphase vesicles. Using different combinations of subphase vesicles and spread surface films a clear correlation between dipalmitoylphosphatidylcholine (DPPC) content and minimum surface tension was observed. Spread phospholipid films containing 50% DPPC over a subphase containing 50% DPPC vesicles did not form stable surface films with a low minimum surface tension. Addition of surfactant protein B (SP-B) to the surface film led to a progressive decrease in minimum surface tension toward 1 mN/m upon cycling, indicating an enrichment in DPPC. Surfactant protein C (SP-C) had no such detectable refining effect on the film. Surfactant protein A (SP-A) had a positive effect on refinement when it was present in the subphase. However, this effect was only observed when SP-A was combined with SP-B and incubated with subphase vesicles before addition to the air bubble containing sample chamber. Comparison of spread films with adsorbed films indicated that refinement induced by SP-B occurs by selective removal of non-DPPC lipids upon cycling. SP-A, combined with SP-B, induces a selective adsorption of DPPC from subphase vesicles into the surface film. This is achieved by formation of large lipid structures which might resemble tubular myelin.     

Studies on lung surfactant replacement in respiratory distress syndrome. Rapid film formation from binary mixed liposomes

Binary mixed liposomes were prepared from dipalmitoylphosphatidylcholine (DPPC) and a minor compound, e.g., egg phosphatidylglycerol (PG) at a ratio of 9:1. Using different preparative techniques, large unilamellar vesicles (LUV), small unilamellar vesicles (SUV) or multilamellar vesicles (MLV) were obtained and were studied with an electron microscope for morphology, with a Wilhelmy balance for spreading and surface tension lowering potential, and in the surfactant-depleted isolated rat lung for their ability to restore expiratory lung capacity. Only the simultaneous investigation of phospholipids by negative staining and thin sectioning allows unequivocal classification of liposomes. The surface-active structures prepared with the technique of Bangham et al. (Bangham, A.D., Hill, M.W. and Miller, N.G.A. (1974) in Methods in Membrane Biology (Korn, E., ed.), Vol. 1, pp. 1-68, Plenum Press, New York) at room temperature are LUV. LUV containing DPPC:PG at a ratio of 9:1 rapidly spread to a film with high surface tension lowering potential. Within 5 min after injection into the subphase they rise to the surface and form a film at the air/liquid interface able to lower the surface tension to less than 1 mN/m at compression. SUV of the same chemical composition, however, are immediately surface-active only when spread directly onto the surface. MLV exhibit poor surface activity. LUV or pure DPPC, applied onto the surface, are weakly surface active within 5 min. DPPC vesicles injected into the subphase at 37 degrees C do not adsorb to any film with surface tension lowering potential in this time. The minor compounds PE, PI, PS, PA, lysoPC enable DPPC to form surface-active films after application on saline at 37 degrees C. Removal of surfactant decreases the expiratory lung capacity of the isolated rat lung from 49.7 to 12.4% at 4 cmH2O. After substitution with natural surfactant, the expiratory lung capacity is twice that of the washed lung (25.9%), but the original distensibility of the native lung is not restituted. The effect of LUV containing DPPC:PG at a ratio of 9:1 is also remarkable (21.2%).     

Influence of lipid saturation grade and headgroup charge: a refined lung surfactant adsorption model

Rapid adsorption of surfactant material to the air/liquid interface of the lung is essential for maintaining normal lung function. The detailed mechanism of this process, however, remains unclear. In this study, we elucidate the influence of lipid saturation grade and headgroup charge of surface layer lipids on surfactant protein (SP)-induced vesicle insertion into monolayers spread at the air/water interface of a film balance. We used dipalmitoylphosphatidlycholine (DPPC),1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) as monolayer lipids doped with either hydrophobic surfactant-specific protein SP-B or SP-C (0.2 and 0.4 mol %, respectively). Vesicles consisting of DPPC/DPPG (4:1, mol ratio) were injected into a stirred subphase to quantify adsorption kinetics. Based on kinetic film balance and fluorescence measurements, a refined model describing distinct steps of vesicle adsorption to surfactant monolayers is presented. First, in a protein-independent step, lipids from vesicles bridged to the interfacial film by Ca²⁺ ions are inserted into defects of a disordered monolayer at low surface pressures. Second, in a SP-facilitated step, active material insertion involving an SP-B- or SP-C-induced flip-flop of lipids occurs at higher surface pressures. Negatively charged lipids obviously influence the threshold pressures at which this second protein-mediated adsorption mechanism takes place.     

Interfacial adsorption of simple lipid mixtures combined with hydrophobic surfactant protein from pig lung.

Hydrophobic pulmonary surfactant protein enriched in SP-C has been mixed in amounts up to 10% by weight with various phospholipids. The lipids used were dipalmitoyl phosphatidylcholine (DPPC), or DPPC plus unsaturated phosphatidylglycerol (PG), or phosphatidylinositol (PI) in molar ratios of 9:1 and 7:3. The protein enhanced the rate and extent of adsorption of each lipid preparation into the air-water interface, and its respreading after compression on a surface balance. Maximum surface pressures attained on compression of monolayers of mixtures of lipids were slightly higher in the presence of protein. The effects on rate and extent of adsorption were proportional to the amount of protein present. Mixtures containing 30 mol% PG or PI adsorbed more readily into the interface than those containing 10% acidic lipid or DPPC alone. Mixtures containing 30% PI were slightly more rapidly adsorbed than those containing 30% PG. The results suggest that mixtures of DPPC with either acidic lipid in the presence of surfactant protein could be effective in artificial surfactants.     

A biophysical mechanism by which plasma proteins inhibit lung surfactant activity

These in vitro experiments study a potential mechanism by which plasma proteins, found in the alveoli during pulmonary edema and hemorrhage, may act to inhibit the surface activity of pulmonary surfactant. The results indicate that the inhibition of the adsorption facility and surface tension lowering ability of a calf lung surfactant extract (CLSE) by albumin, hemoglobin, or fibrinogen may be completely abolished by centrifugation of the protein-surfactant mixture at 12,500 x g. Furthermore, albumin, hemoglobin and fibrinogen (1.25 mg/ml) were shown to inhibit the adsorption of high concentrations of CLSE (0.32 mg/ml), normally unaffected by the addition of exogenous proteins, when the CLSE was injected into the subphase under a preformed protein surface film. Similarly, injection of large amounts of these proteins (2.5 mg/ml) into the subphase beneath a preformed CLSE surface film was without effect, even though the CLSE concentration was only 0.06 mg/ml, a surfactant concentration which is normally inhibited by even small amounts of exogenous protein. Taken together, the data suggest that some proteins may inhibit surfactant function by preventing the surfactant phospholipids from adsorbing to the air-liquid interface, possibly by a competition between the proteins and CLSE phospholipids for space at the air-liquid interface rather than direct molecular interactions between proteins and surfactant.     

Surfactant protein B inhibits secretory phospholipase A2 hydrolysis of surfactant phospholipids

Hydrolysis of surfactant phospholipids (PL) by secretory phospholipases A(2) (sPLA(2)) contributes to surfactant damage in inflammatory airway diseases such as acute lung injury/acute respiratory distress syndrome. We and others have reported that each sPLA(2) exhibits specificity in hydrolyzing different PLs in pulmonary surfactant and that the presence of hydrophilic surfactant protein A (SP-A) alters sPLA(2)-mediated hydrolysis. This report tests the hypothesis that hydrophobic SP-B also inhibits sPLA(2)-mediated surfactant hydrolysis. Three surfactant preparations were used containing varied amounts of SP-B and radiolabeled tracers of phosphatidylcholine (PC) or phosphatidylglycerol (PG): 1) washed ovine surfactant (OS) (pre- and postorganic extraction) compared with Survanta (protein poor), 2) Survanta supplemented with purified bovine SP-B (1-5%, wt/wt), and 3) a mixture of dipalmitoylphosphatidylcholine (DPPC), 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC), and 1-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG) (DPPC:POPC:POPG, 40:40:20) prepared as vesicles and monomolecular films in the presence or absence of SP-B. Hydrolysis of PG and PC by Group IB sPLA(2) (PLA2G1A) was significantly lower in the extracted OS, which contains SP-B, compared with Survanta (P = 0.005), which is SP-B poor. Hydrolysis of PG and PC in nonextracted OS, which contains all SPs, was lower than both Survanta and extracted OS. When Survanta was supplemented with 1% SP-B, PG and PC hydrolysis by PLA2G1B was significantly lower (P < 0.001) than in Survanta alone. When supplemented into pure lipid vesicles and monomolecular films composed of PG and PC mixtures, SP-B also inhibited hydrolysis by both PLA2G1B and Group IIA sPLA2 (PLA2G2A). In films, PLA2G1B hydrolyzed surfactant PL monolayers at surface pressures ≤30 mN/m (P < 0.01), and SP-B lowered the surface pressure range at which hydrolysis can occur. These results suggest the hydrophobic SP, SP-B, protects alveolar surfactant PL from hydrolysis mediated by multiple sPLA(2) in both vesicles (alveolar subphase) and monomolecular films (air-liquid interface).     

膜脂的物理状态对G_s激活AC的影响

用生物膜的拆离与重建方法将从牛脑皮层膜中纯化的激活型ＧＴＰ结合蛋白（Ｇｓ）和腺苷酸环化酶（ＡＣ）在含有不同极性头部或不同脂肪酸侧链的磷脂组成的脂质体上重建形成脂酶体,测定脂酶体中ＡＣ的基础活力及Ｇｓ激活ＡＣ的活力。实验结果表明,磷脂影响ＡＣ的基础活力和Ｇｓ激活ＡＣ活力的顺序依次为：ＰＥ＞ＰＳ＞ＰＣ;含不同脂肪酸侧链的混合磷脂对Ｇｓ的激活活力的影响大于含单一脂肪酸侧链的纯磷脂,如ＰＥＤＰＰＥ,ＰＳＤＰＰＳ,ＰＣＤＰＰＣ。含不同脂肪酸侧链的磷脂影响Ｇｓ的活力的顺序为ＤＬＰＣ＞ＤＭＰＣ＞ＤＰＰＣ。用反映磷脂分子的堆积程度的荧光探剂ＭＣ５４０和脂双层的流动性变化的ＤＰＨ以及专一性标记蛋白质巯基（－ＳＨ）基团的荧光探剂ａｃｒｙｌｏｄａｎ的测定结果表明,不同磷脂影响Ｇｓ的活力的差异主要是由于脂质物理状态的不同所致。     

Chemical synthesis and surface activity of lung surfactant phospholipid analogs. III. Chiral N-substituted ether-amide phosphonolipids

A homologous series of chiral (R) ether-amide phosphonolipid analogs of naturally occurring (R) glycerophospholipids were synthesized and characterized for their interfacial behaviors. The phosphonolipids possess isoteric ether, amide, and phosphonate functions at positions corresponding to the sn-1, sn-2, and sn-3 ester functions, respectively, of naturally occurring glycerophospholipids. All compounds were synthesized with disaturated C16:0 alkyl/acyl moieties to give structural analogy with dipalmitoyl phosphatidylcholine (DPPC), the major glycerophospholipid component of lung surfactant. Further substitutions at the headgroup nitrogen were also used to generate differences in headgroup size and polarity in the synthetic compounds. The surface activity of the ether-amide phospholipids was investigated in terms of adsorption to the air-water interface, together with studies of dynamic respreading after monolayer collapse and surface tension lowering in dynamically compressed spread films and dispersions. Results showed that several ether-amide phosphonolipids had more rapid adsorption and improved dynamic respreading behavior compared to DPPC, plus the ability to lower surface tension into the range of less than 1 to 4 mN/m in spread films and in dispersions under dynamic conditions. In combination with a series of diether phosphonolipids synthetized in a companion study [1], these ether-amide compounds are useful in the development of molecular structure-surface activity correlates for lung surfactant-related materials, and should assist in investigating the specificity of interactions between phospholipids and other pulmonary biological molecules.     

Lipid model membranes for drug interaction study

The present work shows a structural study on the process of incorporation of a hydrophobic drug, Ellipticine (ELPT), into lipid model membranes for drug targeting purpose. The ELPT is an alkaloid that showed an anti-proliferation activity against several types of tumor cells and against the HIV1 virus. We used the zwitterionic lipid dipalmitoyl phosphatidylcholine (DPPC) and four different anionic lipids: cardiolipin (CL), dipalmitoyl phosphatidic acid (DPPA), dipalmitoyl phosphatidylglycerol (DPPG) and dipalmitoyl phosphatidylserine (DPPS), both spread on a Langmuir monolayer and deposited on a solid substrate to mimic a model membrane and study the interaction with the drug ELPT. X-ray reflectivity results pointed toward an increase in drug loading efficiency up to 13.5% mol/mol of ELPT into mixed systems DPPC/CL. This increase in loading efficiency was also accompanied by a slight distortion in the stacking of the bilayers less evidenced after optimization of the molar ratio between the co-lipids. Grazing incidence X-ray diffraction measurements revealed an in-plane lattice distortion due to the presence of hydrocarbon chain backbone ordering in pure systems of DPPC doped with ELPT. The same was not observed in mixed membranes with DPPC/CL and DPPC/DPPA.     

Nuclear magnetic resonance and thermal studies on the interaction between salicylic acid and model membranes

DSC and (1H and 31P) NMR measurements are used to investigate the perturbation caused by the keratolytic drug, salicylic acid (SA) on the physicochemical properties of the model membranes. Model membranes (in unilamellar vesicular (ULV) form) in the present studies are prepared with the phospholipids, dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylethanolamine (DPPE), dipalmitoyl phosphatidic acid (DPPA) and mixed lipid DPPC-DPPE (with weight ratio, 2.5:2.2). These lipids have the same acyl (dipalmitoyl) chains but differed in the headgroup. The molar ratio of the drug to lipid (lipid mixture), is in the range 0 to 0.4. The DSC and NMR results suggest that the lipid head groups have a pivotal role in controlling (i) the behavior of the membranes and (ii) their interactions with SA. In the presence of SA, the main phase transition temperature of (a) DPPE membrane decreases, (b) DPPA membrane increases and (c) DPPC and DPPC-DPPE membranes are not significantly changed. The drug increases the transition enthalpy (i.e., acyl chain order) in DPPC, DPPA and DPPC-DPPE membranes. However, the presence of the drug in DPPC membrane formed using water (instead of buffer), shows a decrease in the transition temperature and enthalpy. In all the systems studied, the drug molecules seem to be located in the interfacial region neighboring the glycerol backbone or polar headgroup. However, in DPPC-water system, the drug seems to penetrate the acyl chain region also.     

The role of the gel <=> liquid-crystalline phase transition in the lung surfactant cycle

Lipid polymorphism plays an important role in the lung surfactant cycle. A better understanding of the influence of phase transitions on the formation of a lipid film from dispersions of vesicles will help to describe the mechanism of action of lung surfactant. The surface pressure (or tension) of dispersions of DPPC, DMPC, and DPPE unilamellar vesicles was studied as a function of temperature. These aggregates rapidly fuse with a clean air-water interface when the system is at their phase transition temperature (Tm), showing a direct correlation between phase transition and film formation. Based on these results, an explanation on how fluid aggregates in the alveolar subphase can form a rigid monolayer at the alveolar interface is proposed.     

The role of hyaluronan in the pulmonary alveolus

The duplex nature of the lining of the pulmonary alveolus has long been appreciated. It appears that surfactant is present at the interface with air where it prevents the collapse of the alveolus by lowering surface tension and that the surfactant rests on an aqueous subphase. This subphase has enough structure to form a smooth, continuous surface over the projections of the epithelial cells and because of its hydrophilic nature it attracts the polar heads of surfactant phospholipids. The chemical composition of the subphase has not been addressed. Type II cells in the wall of the alveolus are specialized to produce surfactant and they also secrete hyaluronan (hyaluronic acid) into the subphase. In solution, molecules of hyaluronan appear to be flexible coils which self-aggregate. The resulting solutions are quite viscous and exhibit non-Newtonian behavior. Hyaluronan binds to cell surface receptors and to proteins in the extracellular matrix. The networks formed with self-aggregated hyaluronan with or without proteins create gels whose properties depend largely upon the molecular weight of the hyaluronan and its concentration. Hyaluronan is also known to interact with phospholipids and has hydrophobic regions which could bind to the hydrophobic surfactant proteins B and C. The working hypothesis presented herein states that hyaluronan interacts with itself and with proteins in the subphase to form a hydrophilic gel. At the epithelial cell layer the components are concentrated due to tethered HA molecules and the gel smooths over cell projections. At the air interface the components are so dilute that a layer which is essentially water is present. The surfactant phospholipids spread on the water. Direct interactions of HA and surfactant phospholipids may also occur and contribute to the stability of the surfactant layer.     

Natural and artificial lung surfactant replacement therapy in premature lambs

The effect of tracheal instillation of surface-active mixtures in premature lambs was studied as an animal model of exogenous surfactant replacement therapy for the respiratory distress syndrome (RDS). Specific mixtures studied were 7:3 (molar ratio) dipalmitoyl phosphatidylcholine (DPPC):egg phosphatidylglycerol (PG) and extracted mixed lipids (with 1% protein) from cow lung lavage (CLL). Preventilatory tracheal instillation of greater than 15 mg/kg of CLL in 10 ml 0.15 M NaCl to premature lambs gave improved alveolar-arterial O2 gradient and blood gases and increased lung compliance, compared with control lambs over a 15-h period. Lambs receiving 7:3 DPPC:PG dispersions were not improved over controls with regard to pressure-volume characteristics and were worse than controls in arterial oxygenation. In terms of in vitro surface properties, both extracted natural CLL and 7:3 DPPC:egg PG were able to lower aqueous surface tension to 1 dyn/cm under dynamic compression. However, the dynamic respreading of CLL films on successive surface cycles was superior to that of 7:3 DPPC:PG. Moreover, after dispersal in 0.15 M NaCl by vortexing (5 mg/80 ml), CLL adsorbed to surface pressure (tau values of 45 dyn/cm within 10 min. 7:3 DPPC:PG adsorbed to significantly lower tau values after subphase dispersal by a variety of methods.     

The cyclic antimicrobial peptide RTD-1 induces stabilized lipid-peptide domains more efficiently than its open-chain analogue

The effects of a mammalian cyclic antimicrobial peptide, rhesus theta defensin 1 (RTD-1) and its open chain analogue (oRTD-1), on the phase behaviour and structure of model membrane systems (dipalmitoyl phosphatidylcholine, DPPC and dipalmitoyl phosphatidylglycerol, DPPG) were studied. The increased selectivity of RTD-1 for anionic DPPG over zwitterionic DPPC was shown by differential scanning calorimetry. RTD-1, at a molar peptide-lipid ratio of 1:100, induced considerable changes in the phase behaviour of DPPG, but not of DPPC. The main transition temperature, Tm, was unchanged, but additional phase transitions appeared above Tm. oRTD-1 induced similar effects. However, the effects were not observable below a peptide:lipid molar ratio of 1:50, which correlates with the weaker biological activity of oRTD-1. Small- and wide-angle X-ray scattering revealed for DPPG the appearance of additional structural features induced by RTD-1 above Tm, which were interpreted as correlated lamellar structures, with increased order of the fatty acyl side chains of the lipid. It is proposed that after initial electrostatic interaction of the cationic rim of the peptide with the anionic DPPG headgroups, leading to stabilized lipid-peptide clusters, the hydrophobic face of the peptide assists in its interaction with the fatty acyl side chains eventually leading to membrane disruption.     

The collapse of monolayers containing pulmonary surfactant phospholipids is kinetically determined

Prior studies have shown that during and after slow compressions of monomolecular films containing the complete set of purified phospholipids (PPL) from calf surfactant at an air/water interface, surface pressures (pi) reach and sustain values that are remarkably high relative to expectations from simple systems with model lipids. Microscopy shows that the liquid-expanded, tilted-condensed, and collapsed phases are present together in the PPL films between 45 and 65 mN/m. The Gibbs phase rule restricts equilibrium coexistence of three phases to a single pi for films with two components but not for more constituents. We therefore determined if the surprising stability of PPL reflects release from the thermodynamic restrictions of simple model systems by the presence of multiple components. Experiments with binary films containing dioleoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine first tested the predictions of the phase rule. The onset of three-phase coexistence, determined by fluorescence microscopy, and its termination, established by relaxation of collapsing films on a captive bubble, occurred at similar pi. Experiments for PPL using the same methods suggested that the three phases might coexist over a range of pi, but limited to approximately 2 mN/m, and extending below rather than above the coexistence pi for the binary films. Our results show that the PPL films at high pi must deviate from equilibrium and that they must then be metastable.     

Adsorption of pulmonary surfactant protein SP-A to monolayers of phospholipids containing hydrophobic surfactant protein SP-B or SP-C: potential differential role for tertiary interaction of lipids, hydrophobic proteins, and SP-A

Surface balance techniques were used to study the interactions of surfactant protein SP-A with monolayers of surfactant components preformed at the air-water interface. SP-A adsorption into the monolayers was followed by monitoring the increase in the surface pressure Deltapi after injection of SP-A beneath the films. Monolayers of dipalmitoylphosphatidylcholine (DPPC):egg phosphatidylglycerol (PG) (8:2, mol/mol) spread at initial surface pressure pi(i) = 5 mN/m did not promote the adsorption of SP-A at a subphase concentration of 0.68 microg/mL as compared to its adsorption to the monolayer-free surface. Surfactant proteins, SP-B or SP-C, when present in the films of DPPC:PG spread at pi(i) = 5 mN/m, enhanced the incorporation of SP-A in the monolayers to a similar extent; the Deltapi values being dependent on the levels of SP-B or SP-C, 3-17 wt %, in the lipid films. Calcium in the subphase did not affect the intrinsic surface activity of SP-A but reduced the Deltapi values produced by the adsorption of the protein to all the preformed films independently of their compositions and charges. The divalent ions likely modified the interaction of SP-A with the monolayers through their effects on the conformation, self-association, and charge state of SP-A. Values of Deltapi produced by adsorption of SP-A to the films of DPPC:PG with or without SP-B or SP-C were a function of the initial surface pressure of the films, pi(i). In the range of pressures 5 相似文献   

Study of calix[4]resorcinarene-dopamine complexation in mixed phospholipid monolayers formed at the air-water interface

We have studied the physical properties of monolayers formed by calix[4]resorcinarene and in mixtures with dipalmitoyl phosphatidylcholine (DPPC) in various molar ratios formed at the air-water interface and at presence of dopamine in water subphase by means of measurements of surface pressure and dipole potential. We showed that both calix[4]resorcinarene as well as its mixture with DPPC form stable monolayers at the water subphase. The presence of dopamine resulted in an increase of the mean molecular area and in a decrease of the compressibility modulus of the monolayers. For mixed monolayers at higher content of calix[4]resorcinarene (> 0.2 molar fraction) a deviation from ideal miscibility took place especially for monolayers in a solid state. This can be connected with formation of aggregates of calix[4] resorcinarene. Lowest miscibility and weakest interaction of dopamine with a monolayer was observed for calix[4]resorcinarene molar fraction of 0.33 in the monolayer.