Colloid Osmotic Pressure in Erythroblastosis Fetalis

Measurements were made of total proteins, albumin, and colloid osmotic pressure on cord blood samples from 15 infants with erythroblastosis fetalis (six of whom were hydropic) and from 151 non-rhesus non-hydropic control infants. The erythroblastotic infants had levels of total protein and albumin which fell within the normal range for gestational age, but their colloid osmotic pressures were abnormally low. It seems that low colloid osmotic pressure may provide a reasonable explanation for the occurrence of hydrops fetalis.     

Continuous measurement of protein osmotic pressure in blood and lymph of sheep

We have continuously measured protein osmotic pressure of blood and lymph in sheep to compare two kinds of needle osmometers (rigid and flexible) with a membrane osmometer (Wescor). We also compared the averaged values of the continuous measurement with osmotic pressure calculated from total protein and albumin fraction, using the Yamada equation. The rigid-needle and membrane osmometers showed excellent correlation (y = 1.00x + 0.06; r greater than 0.99). The flexible-needle osmometer tended to overestimate osmotic pressure (avg 16%). We used the rigid-needle osmometer for continuous measurements of protein osmotic pressure of blood and lymph in anesthetized or unanesthetized sheep to observe changes in protein osmotic pressure of blood and lymph through the three different interventions. The relationship between the theoretical values (x) and the continuous measurements (y) of osmotic pressure was good (y = 0.99x + 0.16, r = 0.97), but after various interventions, the continuously measured protein osmotic pressure tended to exceed the calculated measurements. The continuous measurement should be monitored with spot samples measured in a stationary osmometer or by calculation of osmotic pressure from total protein concentration and albumin fraction.     

Virial coefficients of protein solutions

An osmometer capable of measuring protein osmotic pressures up to 100 cms. of mercury pressure has been described. The principle of the osmometer is to set a given pressure and to permit the protein concentration to equilibrate with the pressure. The higher virial osmotic coefficients of egg albumin in various electrolytes and in 1 m urea as well as a function of NaCl concentration are reported. The virial coefficients of bovine serum albumin and of bovine methemoglobin in 1 m NaCl are also given. It appears that the primary cause for the departure of the osmotic pressure from ideality is due to the covolumes of the proteins.     

Plasma protein osmotic pressure equations and nomogram for sheep

The equations developed by Landis and Pappenheimer (Handbook of Physiology. Circulation, 1963, p. 961-1034) for calculating the protein osmotic pressure of human plasma proteins have been frequently used for other animal species without regard to the fractional albumin concentration or correction for protein-protein interaction. Using an electronic osmometer, we remeasured the protein osmotic pressure of purified sheep albumin and sheep plasma partially depleted of albumin. We measured protein osmotic pressures of serial dilutions over the concentration range 0-180 g/l for albumin and 0-100 g/l for the albumin-depleted proteins at room temperature (26 degrees C). Using a nonlinear least squares parameter-fitting computer program, we obtained the equation of best fit for purified albumin, and then we used that equation together with the measured albumin fraction to obtain the best-fit equation for the nonalbumin proteins. The equation for albumin is IIcmH2O,39 degrees C = 0.382C + 0.0028C2 + 0.000013C3, where C is albumin concentration in g/l. The equation for the nonalbumin fraction is IIcmH2O,39 degrees C = 0.119C + 0.0016C2. Up to 200- and 100-g/l protein concentration, respectively, these equations give the least standard error of the estimate for each of the virial coefficients. The computed number-average molecular weight for the nonalbumin proteins is 222,000. Using the new equations, we constructed a nomogram, based on the one of Nitta and co-workers (Tohoku J. Exp. Med. 135: 43-49, 1981). We tested the nomogram using 144 random samples of sheep plasma and lymph from 31 sheep. We obtained a correlation coefficient of 0.99 between the measured and nomogram estimates of protein osmotic pressure.     

Interstitial albumin concentration measured during growth of perivascular cuffs in liquid-filled rabbit lung.

The growth rate and albumin concentration of interstitial fluid cuffs were measured in isolated rabbit lungs inflated with albumin solution (3 g/dl) to constant airway (Paw) and vascular pressures for up to 10 h. Cuff size was measured from images of frozen lung sections, and cuff albumin concentration (Cc) was measured from the fluorescence of Evans blue labeled albumin that entered the cuffs from the alveolar space. At 5-cmH2O Paw, cuff size peaked at 1 h and then decreased by 75% in 2 h. The decreased cuff size was consistent with an osmotic absorption into the albumin solution that filled the vascular and alveolar spaces. At 15-cmH2O Paw, cuff size peaked at 0.25 h and then remained constant. Cc rose continuously at both pressures, but was greater at the higher pressure. The increasing Cc with a constant cuff size was modeled as diffusion through epithelial pores. Initial Cc-to-airway albumin concentration ratio was 0.1 at 5-cmH2O Paw and increased to 0.3 at 15 cmH2O, a behavior that indicated an increased permeability with lung inflation. Estimated epithelial reflection coefficient was 0.9 and 0.7, and equivalent epithelial pore radii were 4.5 and 6.1 nm at 5- and 15-cmH2O Paw, respectively. The initial cuff growth occurred against an albumin colloid osmotic pressure gradient because a high interstitial resistance reduced the overall epithelial-interstitial reflection coefficient to the low value of the interstitium.     

Theoretical and experimental studies on freezing point depression and vapor pressure deficit as methods to measure osmotic pressure of aqueous polyethylene glycol and bovine serum albumin solutions

For survival in adverse environments where there is drought, high salt concentration or low temperature, some plants seem to be able to synthesize biochemical compounds, including proteins, in response to changes in water activity or osmotic pressure. Measurement of the water activity or osmotic pressure of simple aqueous solutions has been based on freezing point depression or vapor pressure deficit. Measurement of the osmotic pressure of plants under water stress has been mainly based on vapor pressure deficit. However, differences have been noted for osmotic pressure values of aqueous polyethylene glycol (PEG) solutions measured by freezing point depression and vapor pressure deficit. For this paper, the physicochemical basis of freezing point depression and vapor pressure deficit were first examined theoretically and then, the osmotic pressure of aqueous ethylene glycol and of PEG solutions were measured by both freezing point depression and vapor pressure deficit in comparison with other aqueous solutions such as NaCl, KCl, CaCl(2), glucose, sucrose, raffinose, and bovine serum albumin (BSA) solutions. The results showed that: (1) freezing point depression and vapor pressure deficit share theoretically the same physicochemical basis; (2) theoretically, they are proportional to the molal concentration of the aqueous solutions to be measured; (3) in practice, the osmotic pressure levels of aqueous NaCl, KCl, CaCl(2), glucose, sucrose, and raffinose solutions increase in proportion to their molal concentrations and there is little inconsistency between those measured by freezing point depression and vapor pressure deficit; (4) the osmotic pressure levels of aqueous ethylene glycol and PEG solutions measured by freezing point depression differed from the values measured by vapor pressure deficit; (5) the osmotic pressure of aqueous BSA solution measured by freezing point depression differed slightly from that measured by vapor pressure deficit.     

Analysis using a linear viscoelastic model of the in vitro osmotic kinetics of polydisperse synthetic colloids

This study clarifies the contribution to overall osmotic kinetics of colloid osmotic pressure (Pi) and the interaction of synthetic colloids with the membrane. Solutions (6%) of dextran with weight average molecular weight (MW(w)) 68 800 (DEX 70), dextran with MW(w) 40 000 (DEX 40), hydroxyethyl starch with MW(w) 70 000 (HES 70), gelatin with MW(w) 60 000 and albumin were tested. An osmotic flow cell fitted with membranes of molecular weight cutoff size 30 000 or 50 000 was used to measure time-dependent changes in Pi for each of these solutions. A linear viscoelastic model was fitted to the curve describing changes to Pi as a function of time. Values of total effective Pi for DEX 40 and DEX 70 were larger than those for HES 70, gelatin, and albumin. As an index of solute-solvent exchange rate at the membrane surface, these values were in the order DEX 40 > DEX 70, HES 70 > gelatin, albumin. The findings suggest that DEX 40 may be preferable for the temporary restoration of plasma volume because of a heightened initial osmotic force. In contrast, the osmotic force exerted by gelatin is slower to increase but is likely to be longer lasting in vivo as a result of the inhibition of gelatin from penetrating the capillary membrane due to its interaction with negatively charged groups in the endothelial glycocalyx.     

Protein osmotic pressure and the state of water in frog myoplasm

We measured the osmotic pressure of diffusible myoplasmic proteins in frog (Rana temporaria) skeletal muscle fibers by using single Sephadex beads as osmometers and dialysis membranes as protein filters. The state of the myoplasmic water was probed by determining the osmotic coefficient of parvalbumin, a small, abundant diffusible protein distributed throughout the fluid myoplasm. Tiny sections of membrane (3.5- and 12-14-kDa cutoffs) were juxtaposed between the Sephadex beads and skinned semitendinosus muscle fibers under oil. After equilibration, the beads were removed and calibrated by comparing the diameter of each bead to its diameter measured in solutions containing 3-12% Dextran T500 (a long-chain polymer). The method was validated using 4% agarose cylinders loaded with bovine serum albumin (BSA) or parvalbumin. The measured osmotic pressures for 1.5 and 3.0 mM BSA were similar to those calculated by others. The mean osmotic pressure produced by the myoplasmic proteins was 9.7 mOsm (4 degrees C). The osmotic pressure attributable to parvalbumin was estimated to be 3.4 mOsm. The osmotic coefficient of the parvalbumin in fibers is approximately 3.7 mOsm mM(-1), i.e., roughly the same as obtained from parvalbumin-loaded agarose cylinders under comparable conditions, suggesting that the fluid interior of muscle resembles a simple salt solution as in a 4% agarose gel.     

A freeze-fracture transmission electron microscopy and small angle x-ray diffraction study of the effects of albumin, serum, and polymers on clinical lung surfactant microstructure

Freeze-fracture transmission electron microscopy shows significant differences in the bilayer organization and fraction of water within the bilayer aggregates of clinical lung surfactants, which increases from Survanta to Curosurf to Infasurf. Albumin and serum inactivate all three clinical surfactants in vitro; addition of the nonionic polymers polyethylene glycol, dextran, or hyaluronic acid also reduces inactivation in all three. Freeze-fracture transmission electron microscopy shows that polyethylene glycol, hyaluronic acid, and albumin do not adsorb to the surfactant aggregates, nor do these macromolecules penetrate the interior water compartments of the surfactant aggregates. This results in an osmotic pressure difference that dehydrates the bilayer aggregates, causing a decrease in the bilayer spacing as shown by small angle x-ray scattering and an increase in the ordering of the bilayers as shown by freeze-fracture electron microscopy. Small angle x-ray diffraction shows that the relationship between the bilayer spacing and the imposed osmotic pressure for Curosurf is a screened electrostatic interaction with a Debye length consistent with the ionic strength of the solution. The variation in surface tension due to surfactant adsorption measured by the pulsating bubble method shows that the extent of surfactant aggregate reorganization does not correlate with the maximum or minimum surface tension achieved with or without serum in the subphase. Albumin, polymers, and their mixtures alter the surfactant aggregate microstructure in the same manner; hence, neither inhibition reversal due to added polymer nor inactivation due to albumin is caused by alterations in surfactant microstructure.     

Effects of haemorrhage on colloid osmotic pressure in the pigeon

1. Colloid osmotic pressure, plasma osmolality and plasma protein concentration, percentage composition and A/G ratio were measured before and after haemorrhage in the pigeon. 2. Colloid osmotic pressure, total protein, albumin and beta-globulin concentrations decreased significantly immediately post-haemorrhage, but were significantly elevated after one week. 3. Osmolality and A/G ratio values were significantly increased post-haemorrhage. 4. The results are discussed in relation to fluid exchange across capillaries.     

Effective hard particle model for the osmotic pressure of highly concentrated binary protein solutions

The experimentally measured concentration dependence of the osmotic pressure of an equimolar mixture of hen egg ovalbumin and bovine serum albumin at pH 7.0 and 25°C in the presence of 0.15 M NaCl is shown to be quantitatively accounted for by a model in which each protein species is represented by an effective hard sphere. The size of this sphere is determined by analysis of the concentration dependence of the osmotic pressure of the isolated protein.     

A model to explain the osmotic pressure behavior of hemoglobin and serum albumin

Previously published osmotic pressure data on hemoglobin and bovine serum albumin were used to determine the osmotically unresponsive solvent volume per unit dry mass of protein. A model is presented that accounts for the osmotic pressure of globular proteins based on a surface-associated osmotically unresponsive solvent volume. The model also accounts for changes in the osmotically unresponsive solvent volume owing to changes in pH, cosolute salt concentration, protein conformation, and protein aggregation.     

THE KINETICS OF OSMOSIS

It is shown that by combining the osmotic pressure and rate of diffusion laws an equation can be derived for the kinetics of osmosis. The equation has been found to agree with experiments on the rate of osmosis for egg albumin and gelatin solutions with collodion membranes.     

DONNAN EQUILIBRIUM AND THE PHYSICAL PROPERTIES OF PROTEINS : II. OSMOTIC PRESSURE.

1. It had been shown in previous publications that the osmotic pressure of a 1 per cent solution of a protein-acid salt varies in a characteristic way with the hydrogen ion concentration of the solution, the osmotic pressure having a minimum at the isoelectric point, rising steeply with a decrease in pH until a maximum is reached at pH of 3.4 or 3.5 (in the case of gelatin and crystalline egg albumin), this maximum being followed by a steep drop in the osmotic pressure with a further decrease in the pH of the gelatin or albumin solution. In this paper it is shown that (aside from two minor discrepancies) we can calculate this effect of the pH on the osmotic pressure of a protein-acid salt by assuming that the pH effect is due to that unequal distribution of crystalloidal ions (in particular free acid) on both sides of the membrane which Donnan''s theory of membrane equilibrium demands. 2. It had been shown in preceding papers that only the valency but not the nature of the ion (aside from its valency) with which a protein is in combination has any effect upon the osmotic pressure of the solution of the protein; and that the osmotic pressure of a gelatin-acid salt with a monovalent anion (e.g. Cl, NO₃, acetate, H₂PO₄, HC₂O₄, etc.) is about twice or perhaps a trifle more than twice as high as the osmotic pressure of gelatin sulfate where the anion is bivalent; assuming that the pH and gelatin concentrations of all the solutions are the same. It is shown in this paper that we can calculate with a fair degree of accuracy this valency effect on the assumption that it is due to the influence of the valency of the anion of a gelatin-acid salt on that relative distribution of the free acid on both sides of the membrane which Donnan''s theory of membrane equilibrium demands. 3. The curves of the observed values of the osmotic pressure show two constant minor deviations from the curves of the calculated osmotic pressure. One of these deviations consists in the fact that the values of the ascending branch of the calculated curves are lower than the corresponding values in the curves for the observed osmotic pressure, and the other deviation consists in the fact that the drop in the curves of calculated values occurs at a lower pH than the drop in the curves of the observed values.     

The effect of osmotic and mechanical pressures on water partitioning in articular cartilage

X-ray diffraction measurements on native and proteoglycan-free articular cartilage have been made in order to test the dependence of the lateral packing of the collagen molecules on the osmotic pressure gradient, either naturally occurring or externally applied, between the intra- and extrafibrillar compartments. From the information on collagen packing we have been able to calculate, albeit with several assumptions, the amount of intrafibrillar water as a function of pressure. In parallel with the above measurements, we have quantitated, using serum albumin partitioning, the intrafibrillar water in proteoglycan-free cartilage, as a function of mechanically applied pressure. The results of both sets of experiments lead to the conclusion that the molecular packing density, and hence the intrafibrillar water content, are a function of the osmotic pressure difference between the extrafibrillar and intrafibrillar spaces or the equivalent mechanically applied pressure. The determination of intrafibrillar water has enabled us to calculate, from measured values of fixed charge density, the internal osmotic pressure of cartilage specimens, both in compressed and uncompressed states.     

ION SERIES AND THE PHYSICAL PROPERTIES OF PROTEINS. I

1. This paper contains experiments on the influence of acids and alkalies on the osmotic pressure of solutions of crystalline egg albumin and of gelatin, and on the viscosity of solutions of gelatin. 2. It was found in all cases that there is no difference in the effects of HCl, HBr, HNO₃, acetic, mono-, di-, and trichloracetic, succinic, tartaric, citric, and phosphoric acids upon these physical properties when the solutions of the protein with these different acids have the same pH and the same concentration of originally isoelectric protein. 3. It was possible to show that in all the protein-acid salts named the anion in combination with the protein is monovalent. 4. The strong dibasic acid H₂SO₄ forms protein-acid salts with a divalent anion SO₄ and the solutions of protein sulfate have an osmotic pressure and a viscosity of only half or less than that of a protein chloride solution of the same pH and the same concentration of originally isoelectric protein. Oxalic acid behaves essentially like a weak dibasic acid though it seems that a small part of the acid combines with the protein in the form of divalent anions. 5. It was found that the osmotic pressure and viscosity of solutions of Li, Na, K, and NH₄ salts of a protein are the same at the same pH and the same concentration of originally isoelectric protein. 6. Ca(OH)₂ and Ba(OH)₂ form salts with proteins in which the cation is divalent and the osmotic pressure and viscosity of solutions of these two metal proteinates are only one-half or less than half of that of Na proteinate of the same pH and the same concentration of originally isoelectric gelatin. 7. These results exclude the possibility of expressing the effect of different acids and alkalies on the osmotic pressure of solutions of gelatin and egg albumin and on the viscosity of solutions of gelatin in the form of ion series. The different results of former workers were probably chiefly due to the fact that the effects of acids and alkalies on these proteins were compared for the same quantity of acid and alkali instead of for the same pH.     

Theoretical and Practical Aspects of Albumin Esterase Activity

Russian Journal of Bioorganic Chemistry - Unlike many other plasma proteins, albumin is barely glycosylated and plays an important role in maintaining the colloidal osmotic blood pressure; it can...     

The origin and consequences of concentration dependence in gel chromatography

Concentration dependence of elution volume was determined for Blue Dextran 2000, Dextran 500, Dextran sulphate 500 and bovine serum albumin on columns of Sephadex G-100 equilibrated with sodium phosphate buffer, I 0.1, pH6.8. From the results for Dextran 500, it was shown that a linear relation exists between elution volume and the corresponding osmotic pressure calculated for the same concentration and incorporating the term containing the second virial coefficient. This relationship was used to predict the concentration dependence of elution volume for bovine serum albumin and myoglobin, proteins that partially penetrate Sephadex G-100. Possible consequences of osmotic effects are considered in relation to various types of column experiments, including differential chromatography.     

A sensitive and accurate gel osmometer

1. A bilayer strip, cut from a thin layer of cross-linked polyacrylamide gel cast on to cellulose tissue, forms an open circular loop whose ends are close together. Shrinkage of the gel, in response to the osmotic pressure of a non-penetrating solution, causes a proportional separation of the ends of the loop. This is measured with a microscope and micrometer eyepiece. 2. The resulting effective sensitivity is about 30 times that of the Sephadex-bead osmometer (Ogston & Wells, 1970), i.e. of the order of 5Pa, comparable with that of a membrane osmometer. Use of gel up to 70% (w/v) allows the measurement of molecular weights, as low as 1500 in favourable cases, with an accuracy of 1-2%. The useful range of osmotic pressure is up to 5kPa. A single measurement requires 0.5ml of solution. Equilibration is completed in 20-30min. 3. The method is illustrated by measurements on human serum albumin, ovalbumin, cytochrome c, samples of dextrans, polyvinyl alcohol, and polyethylene glycols 6000 and 1000.     

Constant-volume hydrogel osmometer: a new device concept for miniature biosensors

A new type of biosensor is proposed that combines the recognition properties of "intelligent" hydrogels with the sensitivity and reliability of microfabricated pressure transducers. In the proposed device, analyte-induced changes in the osmotic swelling pressure of an environmentally responsive hydrogel are measured by confining it within a small implantable enclosure between a rigid semipermeable membrane and the diaphragm of a miniature pressure transducer. Proof-of-principle tests of this device were performed in vitro using pH-sensitive hydrogels, with osmotic deswelling data for the same hydrogels used as a benchmark for comparison. The swelling pressure of the hydrogel was accurately determined from osmotic deswelling measurements against reservoirs of known osmotic stress. Values of swelling pressure vs salt concentration measured with a preliminary version of the sensor agree well with osmotic deswelling results. Through modification of the hydrogel with various enzymes or pendant binding moieties, the sensor has the potential to detect a wide range of biological analytes with good specificity.