Of the individual potentials which comprise the potential profile of a membrane, the least well understood is the dipole potential. In general, the dipole potential is manifested between the hydrocarbon interior of the membrane and the first few water layers adjacent to the lipid head groups. Changes in dipole potential caused by spreading a lipid at an air- or oil-water interface can be measured directly and the dipole potential of bilayers can be estimated from the conductances of hydrophobic ions. For a typical phospholipid, like phosphatidylcholine, its measured value is approximately 400 mV in monomolecular films and approximately 280 mV in bilayer membranes, with the hydrocarbon region being positive relative to the aqueous phase. The difference between dipole potentials measured in monolayers and bilayer membranes appears to arise from the use of the lipid-free air- or oil-water interface as the reference point for monolayer measurements and can be corrected for. The species-specific correction term is a lipid concentration-independent potential, the existence of which suggests the ability of lipid headgroups to globally reorganize water structure at the interface. The dipole potential arises from the functional group dipoles of the terminal methyl groups of aliphatic chains, the glycerol-ester region of the lipids and the hydrated polar head groups. Classical methods for obtaining partial dipole moments for each of the three contributing regions are all based on questionable assumptions and give conflicting results. More sophisticated mean-field models of dipole potential origin recognize the important role of interfacial water in determining its value but still cannot adequately describe the microscopic nature of the interactions from which it arises. In part this is because the dipole potential develops in a region over which the dielectric constant of the medium is changing from 2 to 80. Despite of our limited understanding of the dipole potential, it is an important regulator of membrane structure and function. Membrane-membrane and membrane-ligand interactions are regulated by the hydration force, the value of which can be related to the dipole potential of the membrane. For thermotropically phase-separated or multicomponent membranes the size and shape of lipid domains is controlled by the balance between the line tension at the domain borders and the difference in dipole density between the domains. Line tension tends to make the domains compact and circular whereas dipole repulsion promotes transitions to complex domain shapes with larger perimeters.(ABSTRACT TRUNCATED AT 400 WORDS)

When spread from organic solvents onto electrolyte solutions, the Ca2+ ionophores A23187 (I) and X537A (II) formed films with relatively high surface pressures potentials. Ionophores I had collapse pressures between 16 and 19 dynes/cm and nearly equal surface activity on distilled water and on 1000 mEq of either sodium chloride or calcium chloride. Film pressure did not reveal appreciable ion selectivity. However, the surface potential of I on calcium chloride solution was higher than that on sodium chloride, and the potential difference, delta(deltaV), of 40 mv was independent of the electrolyte concentration. In contrast, the ion selectivity of II was dependent on the electrolyte concentrations since the delta(deltaV) value between calcium chloride and sodium chloride was maximal (130 mv) on 1000 mEq and negligible on 500- and 2000-mEq salt solutions. The isotherms of phospholipid-ionophore films were markedly different from those of the individual components, although they revealed ionophore characteristics at low film pressures and phospholipid behavior at high film pressures. The magnitude of the surface potential indicated that dipalmitoyl phosphatidylcholine enhanced, whereas mitochondrial lipid and cardiolipin reduced, the preference of the two ionophores for Ca2+ over Na+. Since the ion selectivity was manifested most at both high electrolyte and high lecithin concentrations, the ionophore probably prefers the low dielectric constant of neutral lipid membranes to complex with the selected cation.

Hemolytic delta-toxin from Staphylococcus aureus was soluble in either water, methanol or chloroform/methanol (2 : 1, v/v). The toxin spread readily from distilled water into films with pressures (pi) of 10 dynes/cm on water and 30 dynes/cm on 6 M urea; from chloroform/methanol it produced 40 dynes/cm pressure on distilled water. The toxin adsorbed barely from water (pi = 1 dyne/ cm) but it did rapidly from 6 M urea (pi = 35 dynes/cm). The protein films had unusually high surface potentials, which increased with the film pressure and decreased with increasing both pH and urea concentration in the aqueous phase. The fluorescence of 1-aniline 8-naphthalene sulfonate with delta-toxin was much greater than that with RNAase and dipalmitoyl phosphatidylcholine itself, indicating probably a marked lipid-binding character of the toxin. By circular dichroism the alpha-helix content of delta-toxin was 42% in water, 45% in methanol, 24% in 6 M urea. Infrared spectroscopy showed predominant alpha-helix in both 2H2O and deuterated chloroform/methanol as well as in films spread from either solvent on 2H2O. In spreading from 6 M [2H]urea, in which the major infrared absorption was that of [2H]urea with peaks at 1600 and 1480 cm(-1), the delta-toxin film showed prevalently non-alpha-helix structures with major peak intensities at 1633 cm(-1)> 1680 cm(-1), indicating the appearance of new beta-aggregated and beta-antiparallel pleated sheet structures in the film. The data prove that (1) high pressure protein films can consist of alpha-helix as well as non-alpha-helix structures and, differently from another cytolytic protein, melittin, delta-toxin does not resume the alpha-helix conformation in going into the film phase from the extended chain in 6 M urea;(2) conformational changes are important in the transport of proteins from aqueous to lipid or membrane phase;(3) delta-toxin is by far more versatile in structural dynamics and more surface active than alpha-toxin.

When spread from organic solvents onto electrolyte solutions, the Ca2+ ionophores A23187 (I) and X537A (II) formed films with relatively high surface pressures potentials. Ionophores I had collapse pressures between 16 and 19 dynes/cm and nearly equal surface activity on distilled water and on 1000 mEq of either sodium chloride or calcium chloride. Film pressure did not reveal appreciable ion selectivity. However, the surface potential of I on calcium chloride solution was higher than that on sodium chloride, and the potential difference, delta(deltaV), of 40 mv was independent of the electrolyte concentration. In contrast, the ion selectivity of II was dependent on the electrolyte concentrations since the delta(deltaV) value between calcium chloride and sodium chloride was maximal (130 mv) on 1000 mEq and negligible on 500- and 2000-mEq salt solutions. The isotherms of phospholipid-ionophore films were markedly different from those of the individual components, although they revealed ionophore characteristics at low film pressures and phospholipid behavior at high film pressures. The magnitude of the surface potential indicated that dipalmitoyl phosphatidylcholine enhanced, whereas mitochondrial lipid and cardiolipin reduced, the preference of the two ionophores for Ca2+ over Na+. Since the ion selectivity was manifested most at both high electrolyte and high lecithin concentrations, the ionophore probably prefers the low dielectric constant of neutral lipid membranes to complex with the selected cation.

Transformed cells from human lung carcinoma (Line A549), resembling type II pneumocytes, were cultured in monolayer at 37 degrees C and incubated for five hours with 3H-choline and 14C-palmitate in the presence of various concentrations of prostaglandins (PGS) E2 and F2alpha. In the control (no PG) the level of % palmitate incorporation was 13.5 x as high as that of choline, after taking isotope dilution into account. Between the concentrations studied, 0.1 and 10 muM, both prostaglandins stimulated markedly the incorporation of both precursors, though choline up to 3 x better than palmitate. This was indicated by a change in the palmitate/choline incorporation ratio from 13.5 to as low as 4.2. At the lowest PG concentration, 0.1 muM, PGE2 was much more effective than PGF2alpha in stimulating the incorporation of both precursors.

In line with previous findings at 25 degrees C, solutions of serum albumin in the subphase stabilized the surface activity of DPL spread films at 25 degrees C as well as 37 degrees C. In contrast, films adsorbed from mixtures of DPL and albumin exhibitied a marked inhibitory action of the albumin on DPL activity. The inhibitory effect increased with the relative protein concentration but, with albumin/DPL ratios smaller than 2, the DPL activity was regained gradually with cycling. With larger albumin/DPE negative effect of albumin was counteracted by higher temperatures (37 degrees C vs 25 degress C) and modest cholesterol concentrations; with greater cholesterol concentrations the known inhibitory effect of cholesterol prevailed. The inhibitory effect of albumin was potentiated by humidity; saturation of the atmosphere with water vapor at 37 degrees C abolished the DPL character of DPL-RSA mixtures and prevented its return (zero surface tension) upon reversal of the atmosphere from saturated water vapor to dry air. The data are important in the interpretation of the surface activity of pulmonary washings and other pulmonary extracts.

Ketamine solutions did not form a film (pi=0) but had an appreciable surface potential (delta V=500 mv), indicating a significant array of +/- oriented charge dipoles at the air-water interface, as opposed to calcium chloride solutions whose delta V was zero. The delta V values of ganglioside films spread on the aqueous phase varied in the order water less than sodium chloride less than calcium chloride less than ketamine hydrochloride. At equivalent concentrations, calcium chloride was 500 times as effective as sodium chloride, and ketamine at the clinical concentrations of 10-20 microgram/ml (36-72 micrometer) was 6000 times as effective as calcium chloride in raising the surface potential of gangliosides; the delta V effect with mitochondrial lipid was in the reverse order; water less than sodium chloride = ketamine hydrochloride less than calcium chloride. This calcium-ketamine inversion indicates a unique specificity of ketamine for gangliosides. Since ketamine acts on the brain and did not affect mitochondrial respiration, the surface potential data suggest that part of the mechanism of action of ketamine could be its interaction with synaptic surfaces and, specifically, with the sialic acid of gangliosides and/or glycoproteins present on the synaptic membrane surface.

Cell lines derived from type II lung cells were used to study interplays of substances affecting incorporation of labeled precursors [1(-14)C]palmitate and [methyl-3H]choline into phosphatidyl choline. Ethanol stimulated markedly biosynthesis of dipalmitoyl phosphatidyl choline in cloned rabbit lung cells; the stimulating action of ethanol was reduced very much by cortisol and less by ritodrine. In the presence of 0.1 microM isoproterenol, two prostaglandins, E2 and F2alpha, caused marked depressions in the incorporation of both precursors by cell line A 549 derived from human lung adenocarcinoma. One concluded that among the agents studied, ethanol and cortisol are potent antagonists, and so were also the prostaglandins and isoproterenol.

Both high pH at 25 degrees C and humidity at 37 degrees C prevent DPL films from attaining zero surface tension, whereas humidity at 25 degrees C and high pH at 37 degrees C do not. At 37 degrees C DPL lowered surface tension to zero when spread from organic solvent or when absorbed from aqueous 0.15 M NaCl in the surface balance in which the surface film was exposed to the room air (dry film). Upon saturation of the atmosphere with water vapor in equilibrium with the aqueous phase at 37 degrees C in a closed chamber, DPL lost the ability to produce zero surface tension, and the gamma min of the DPL film increased from zero to 22 dyne/cm. Addition of DPL in chloroform to distilled water before dispersion by sonication did not prevent the effect of the humidity. However, when the chloroform solution of DPL was added to 0.15 M NaCl before sonication, the adsorbed film produced immediately a stable gamma min of zero in a saturated atmosphere, 37 degrees C. In the absence of chloroform, with DPL adsorbed from either distilled water or 0.15 M NaCl, the effect of humidity was reversed either by removing the chamber and returning the wet film to room air or by introducing small quantities of dispersing agents such as cholesteryl palmitate. However, whereas the effect of humidifying the air was reversible indefinitely, the effect of cholesteryl palmitate (zero surface tension, wet or dry film) was irreversible. This means that there are substances or conditions that can assist DPL films in maintaining zero surface tension when such films are exposed to humidity-saturated air at 37 degrees C.