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PubMed1954

Membrane potentials in the Donnan equilibrium. II.

Measurements were made of electromotive force in the Donnan equilibrium of systems containing dilute solutions of protein and acid. Removal of the membrane produced a decrease of no more than 2 to 4 mv. in electromotive force, while the membrane potentials, as estimated by the usual arbitrary assumption, were of the order of 12 to 34 mv. Ion ratios, as calculated from analyses for total chloride, were definitely greater than those calculated from the electromotive force of cells with salt bridges, as if there had been combination of some of the chloride ion with protein.

Chlorides↗
PubMed1956

Osmotic diuresis and its effect on total electrolyte distribution in plasma and urine of the aglomerular teleost, Lophius americanus.

Quantitative evaluations have been made of the chief anions and cations in plasma, urine, and pericardial fluid taken both from freshly captured goosefish and from those undergoing "laboratory diuresis." Measurements included: Na, K, Ca, Mg, Cl, SO(4), PO(4), protein, HCO(3), NH(3), pH, titratable acidity, freezing point depression, creatine, trimethylamine oxide, and plasma volume. The total patterns of electrolyte distribution in these body fluids are presented. The morphologically undifferentiated aglomerular tubule acts as a barrier to the free diffusion of monovalent electrolytes, while transporting actively the divalent ions, especially Mg. Urine taken from freshly captured fish is hypotonic to plasma, low in electrolyte, and as much as 50 per cent of its total osmolarity is accounted for by nitrogenous components. Of these creatine is transported most actively by the renal tubule cells. With the onset of diuresis immediately after capture, plasma osmolarity slowly rises and urine suddenly becomes isotonic with plasma as chloride floods into the urine. The active movement of Mg continues during diuresis and urine/plasma concentration ratios of 100 or more are sustained for days while the animals are kept in the laboratory. Na follows chloride and never reaches 50 per cent of plasma values, and K never appears in urine in more than mere traces. Electrolytes in this system are viewed as not being in true equilibrium but rather as constituting a biological steady state with the distribution across renal cells being maintained against passive diffusion by the expenditure of cellular energy.

Animals↗
PubMed1956

The role of water in protoplasmic permeability and in antagonism.

The behavior of the cell depends to a large extent on the permeability of the outer non-aqueous surface layer of the protoplasm. This layer is immiscible with water but may be quite permeable to it. It seems possible that a reversible increase or decrease in permeability may be due to a corresponding increase or decrease in the water content of the non-aqueous surface layer. Irreversible increase in permeability need not be due primarily to increase in the water content of the surface layer but may be caused chiefly by changes in the protoplasm on which the surface layer rests. It may include desiccation, precipitation, and other alterations. An artificial cell is described in which the outer protoplasmic surface layer is represented by a layer of guaiacol on one side of which is a solution of KOH + KCl representing the external medium and on the other side is a solution of CO(2) representing the protoplasm. The K(+) unites with guaiacol and diffuses across to the artificial protoplasm where its concentration becomes higher than in the external solution. The guaiacol molecule thus acts as a carrier molecule which transports K(+) from the external medium across the protoplasmic surface. The outer part of the protoplasm may contain relatively few potassium ions so that the outwardly directed potential at the outer protoplasmic surface may be small but the inner part of the protoplasm may contain more potassium ions. This may happen when potassium enters in combination with carrier molecules which do not completely dissociate until they reach the vacuole. Injury and recovery from injury may be studied by measuring the movements of water into and out of the cell. Metabolism by producing CO(2) and other acids may lower the pH and cause local shrinkage of the protoplasm which may lead to protoplasmic motion. Antagonism between Na(+) and Ca(++) appears to be due to the fact that in solutions of NaCl the surface layer takes up an excessive amount of water and this may be prevented by the addition of suitable amounts of CaCl(2). In Nitella the outer non-aqueous surface layer may be rendered irreversibly permeable by sharply bending the cell without permanent damage to the inner non-aqueous surface layer surrounding the vacuole. The formation of contractile vacuoles may be imitated in non-living systems. An extract of the sperm of the marine worm Nereis which contains a highly surface-active substance can cause the egg to divide. It seems possible that this substance may affect the surface layer of the egg and cause it to take up water. A surface-active substance has been found in all the seminal fluids examined including those of trout, rooster, bull, and man. Duponol which is highly surface-active causes the protoplasm of Spirogyra to take up water and finally dissolve but it can be restored to the gel state by treatment with Lugol solution (KI + I). The transition from gel to sol and back again can be repeated many times in succession. The behavior of water in the surface layer of the protoplasm presents important problems which deserve careful examination.

Animals↗
PubMed1956

The freezing point depression of mammalian tissues in relation to the question of osmotic activity of cell fluid.

The freezing point depression of freshly excised frozen tissues, pulverized in a hydraulic press or in a mortar, is greater than that of plasma. Even at 0 degrees C. the freezing point depression of such homogenates increases significantly with time. Dilution data indicate that such freezing point data are valid. The presence of intact cells has been shown in smears of tissues pulverized in a mortar, but not in smears of those crushed in a hydraulic press. The osmolarity of various diluent solutions affects the calculated osmotic activity of tissue homogenates presumably because of delayed diffusion between the diluent and cell fluid. With a hypertonic NaCl diluent, spuriously low values of tissue osmotic activity are found from calculations assuming instantaneous mixing between homogenates and diluents. The limitations of data from cryoscopic experiments and from tissue-swelling experiments are discussed in relation to the basic question of whether or not cell fluid is isotonic to extracellular fluid.

Animals↗
PubMed1957

Electroosmosis in Nitella.

The role of electroosmosis was studied directly in Nitella. The cells were mounted in a water-tight barrier between two chambers containing reversible electrodes for the application of potentials, and fitted with calibrated capillaries to measure water movement. No water movement was found when small existing bioelectric potentials were short-circuited through an external connection, nor when external potentials up to 1 or 2 volts were applied (producing currents up to 5 microa). Higher potentials (up to 10 volts) caused small movements of water, toward the negative pole. Larger and often irreversible water movements were produced by potentials up to 20 volts-sometimes persisting after current flow. A variety of evidence suggests that the effects are caused by injury at the cathodal end of the cell, allowing water to be attracted osmotically at the intact end and forced out at the injured end (transosmosis). This injury is reversible under small applied potentials, irreversible after large ones (100 to 200 times the natural bioelectric values). Such water flows persist in low salt concentrations (up to 0.09 M NaCl) but almost completely vanish in isotonic (0.26 M) mannitol. This confirms the osmotic, rather than the electroosmotic nature of the water movement. It is estimated that electroosmosis cannot account for more than 1 per cent of the water movement (or turgor) in Nitella cells. The dead cellulose walls display a small electroosmotic water flow at very high current densities (under 20 volts applied potential).

Electroosmosis↗
PubMed1959

Electrokinetic membrane processes in relation to properties of excitable tissues. I. Experiments on oscillatory transport phenomena in artificial membranes.

An artificial system is studied consisting of salt solutions of different concentrations separated by a porous, "charged" membrane, through which a constant electric current is passed. Experiments on such systems demonstrate rhythmic variations of the transmembrane potential and the membrane resistance, which are concomitant with an oscillatory streaming of water solution across the membrane. The repetitive oscillations can be of a damped or undamped type dependent on the "stimulating" current density. A qualitative discussion of the mechanism of the oscillations is given. It centers around the periodic resistance changes in the membrane, which result from a complicated interplay between the driving forces present. The importance of electro-osmotic effects is emphasized. A few comparisons relating to possible electrophysiological implications are presented. In the metastable state of this membrane oscillator, "make" and "break" responses can be triggered by electric as well as by mechanical (pressure) "stimuli."

Biological Transport↗
PubMed1959

Electrokinetic membrane processes in relation to properties excitable tissues. II. Some theoretical considerations.

A quantitative theory is presented for the behavior of a membrane-electrolyte system subject to an electric current flow (the "membrane oscillator"). If the membrane is porous, carries "fixed charges," and separates electrolyte solutions of different conductances, it can be the site of repetitive oscillatory changes in the membrane potential, the membrane resistance, and the hydrostatic pressure difference across the membrane. These events are accompanied by a pulsating transport of bulk solutions. The theory assumes the superposition of electrochemical and hydrostatic gradients and centers round the kinetics of resistance changes within the membrane, as caused by effects from diffusion and electro-osmotic fluid streaming. The results are laid down in a set of five simple, basic expressions, which can be transformed into a pair of non-linear differential equations yielding oscillatory solutions. A graphical integration method is also outlined (Appendix II). The agreement between the theory and previous experimental observations is satisfactory. The applied electrokinetic concepts may have importance in relation to analyses of the behavior of living excitable cells or tissues.

Biological Transport↗
PubMed1959

The potential of water in mammalian tissues.

Melting point depression was used as an index of the water potential of rat tissues and serum. Organs removed from anesthetized rats were immediately frozen in liquid nitrogen and ground with mortar and pestle. Aliquots of the resulting frozen powder were suspended in chilled liquid silicone. While the suspension was vigorously stirred and warmed at a constant rate, the temperature of the melting mixture was measured. The melting curves of rat muscle, liver, heart, and brain were not significantly different from those of rat serum. The melting curve depression of whole kidney was greater than that of serum; this was demonstrated to be due to hypertonicity of the renal medullary area alone. It was demonstrated that autolysis will rapidly increase the depression of the melting curve of tissue. It is concluded that within the limits of the method used the melting point depression, and hence the water potential, of intracellular and extracellular fluids is the same.

Animals↗
PubMed1960

Determination of equivalent pore radius for human red cells by osmotic pressure measurement.

A new method has been developed to measure the equivalent pore radius in cellular membranes, and has been applied to human red cells. When red cells are suddenly introduced into a non-isosmolar concentration of non-lipid-soluble non-electrolyte molecules, water will enter or leave the cell. The rate of cell swelling or shrinking is determined and extrapolated to zero time to give the initial rate of volume change. By suitable adjustment of the concentration of the external solution the initial rate may be brought to zero. The transient equilibrium concentration, determined by interpolation from experimental data, gives a measure of Staverman's reflection coefficient, sigma. The zero time method has enabled us to determine sigma for nine permeant molecules. sigma is directly related to the equivalent pore radius; the experimental data lead to a value of 4.2 A for the equivalent pore radius in man, in good agreement with the previous figure of 3.5 A given by Paganelli and Solomon. The zero time method offers a number of advantages over previous methods for determination of this parameter. It requires no measurement of the rate of water entrance into the cell, and is essentially independent of the kinetics of cell swelling. It may be applied to a variety of living cells so that many additional membranes may now be characterized in terms of their equivalent pore radius.

Erythrocytes↗
PubMed1960

Osmotic flow of water across permeable cellulose membranes.

Direct measurements have been made of the net volume flow through cellulose membranes, due to a difference in concentration of solute across the membrane. The aqueous solutions used included solutes ranging in size from deuterated water to bovine serum albumin. For the semipermeable membrane (impermeable to the solute) the volume flow produced by the osmotic gradient is equal to the flow produced by the hydrostatic pressure RT DeltaC, as given by the van't Hoff relationship. In the case in which the membrane is permeable to the solute, the net volume flow is reduced, as predicted by the theory of Staverman, based on the thermodynamics of the steady state. A means of establishing the amount of this reduction is given, depending on the size of the solute molecule and the effective pore radius of the membrane. With the help of these results, a hypothetical biological membrane moving water by osmotic and hydrostatic pressure gradients is discussed.

Cell Membrane↗
PubMed1962

Cat heart muscle in vitro. III. The extracellular space.

The "osmotic gradient" method, an intracellular microelectrode technique for determining whether an uncharged, water-soluble molecule enters cells or remains extracellular, is described. Using this method, a series of carbohydrates of graded molecular size were examined. In cat papillary muscles mannitol, molecular radius 4.0 A, remained extracellular while arabinose, molecular radius 3.5 A entered the cells. Measurement of the simultaneous uptake of H(3)-mannitol and C(14)-inulin showed that mannitol equilibrates with 40 per cent of total water in 1 hour, after which the mannitol space does not further increase. By contrast, inulin, molecular radius approximately 15 A, equilibrates with 24 per cent of total water in 1 hour; thereafter the inulin space continues to increase very slowly. The intracellular K concentrations are significantly higher and the intracellular Na and Cl concentrations significantly lower when mannitol rather than inulin is used to measure the extracellular space. The intracellular Cl concentration determined with Cl(36) or Br(82) is significantly higher than that calculated from the membrane potential assuming a passive Cl distribution. In addition, it is shown that choline enters and is probably metabolized by the cells of papillary muscle.

Animals↗
PubMed1964

THE OSMOTICALLY FUNCTIONAL WATER CONTENT OF THE HUMAN ERYTHROCYTE.

Experiments were directed toward estimation of the magnitude of error incurred by the presumption of idealized osmometric behavior in the author's recent studies of monosaccharide transport through the human erythrocyte membrane. Thick suspensions of washed cells in isotonic buffered balanced salt medium were mixed in fixed proportions with varying dilutions of a concentrate of either (a) the mixed chlorides of the medium, or (b) glucose in the isotonic medium, and the resultant freezing point and hematocrit values determined. The form of the responses in the tonicity and the cell volume, as functions of the variable dilution of sugar or salts, conformed consistently with relations derived from the classical van't Hoff-Boyle-Mariotte pressure-volume relation. However, the effective cell water contents appeared substantially less than the weight lost in conventional drying, and varied somewhat according to the index used: expressed as grams of H(2)O per milliliter of cells at isotonic volume, the cell water implied by the hematocrit behavior was 0.614 +/- 0.015 (SD); by the salt tonicity response, 0.565 +/- 0.027; by the immediate glucose tonicity response, 0.562 +/- 0.044; and by the equilibrium glucose tonicities, 0.589 +/- 0.043. Olmstead's reports of gross deviation from the van't Hoff relation, in the rabbit red cell's responses to tonicity displacement, are attributed primarily to a systematic aberration in his method of data analysis, the observations themselves agreeing substantially with the present findings.

Biological Transport↗
PubMed1964

EFFECTS OF D2O AND OSMOTIC GRADIENTS ON POTENTIAL AND RESISTANCE OF THE ISOLATED FROG SKIN.

Exposure of the outside surface of isolated frog skin (R. pipiens and R. catesbeiana) to sulfate solution made up with D(2)O decreased skin potential and resistance. Exposure of the inside surface to D(2)O solution decreased the potential slightly but increased the resistance. The changes were linearly related to the D(2)O concentration. Since D(2)O acts like a hyperosmotic solution, the skin potential and resistance were studied upon exposure to solution made hyperosmotic by addition of sucrose, mannitol, acetamide, urea, thiourea, Na(2)SO(4), or K(2)SO(4). Skin potential and resistance decreased when the outside solution was made hyperosmotic. The changes depended upon the concentration and the nature of the solute. Thiourea and urea solutions were the most effective. Treatment of the inside surface gave relatively small decreases in potential; the resistance either increased or remained unchanged. These effects appeared to depend upon the direction of the osmotic gradient across the skin rather than upon the value of the osmolarity compared to normal body fluids. Experiments with a series of six polyhydric alcohols from methanol to mannitol and the polysaccharides, sucrose and raffinose, showed adonitol with 5 carbons to decrease the potential the most. Smaller and larger compounds of this set gave lesser effects. As yet no consistent explanation of the effects is forthcoming, but their demonstration calls for caution in the indiscriminate use of solutes such as mannitol or sucrose "to make up the osmolality" and in the neglect of urea because "it penetrates freely."

Animals↗
PubMed1964

MEMBRANE RESISTANCE OF HUMAN RED CELLS.

A method has been devised to measure the specific membrane resistance of single human red cells. The cells were sucked into a 3 to 5 micron diameter pore in the end of a glass tube. By passing a small current through the cells, the total cell resistance was measured. The dimensions of the cell were measured optically and the specific membrane resistance was then calculated. Leakage of current between the cell and the walls of the pore was minimized by filling this region with isotonic sucrose. The measured specific membrane resistance values of four human red cells were 6.3, 6.32, 10.0, and 19.7 ohm-cm(2).

Erythrocytes↗
PubMed1964

WATER TRANSFER AND CELL STRUCTURE IN ISOLATED CRAYFISH MUSCLE FIBERS.

Changes in volume of crayfish single muscle fibers in response to changes in ionic or electrical conditions have been studied in conjunction with electrophysiological measurements and electron microscopic examinations. The occurrence of at least three mechanisms of water movements is revealed, two being processes which are superimposed on the normal osmotic water movement that results from a change in the concentration of solute in the medium. Differences between the time courses of the changes in volume and potential on changing K(i)/K(o) indicate that water may be distributed unequally for a time within compartments of the fiber. Electron micrographs reveal a selective accumulation of water at the periphery of the fiber under certain conditions. A correlation of H(2)O transfer with a change in membrane potential is apparent in crayfish muscle fibers and is probably due to electroosmotic effects. Electrokinetic water movements are produced whenever the membrane potential is changed to a considerable degree by changing the level of K and/or Cl in the medium, or by applying currents with an intracellular microelectrode. Depolarizations cause shrinkage. Hyperpolarizations or repolarizations cause swelling. The volume changes are independent of the occurrence or absence of swelling in the anion-permselective transverse tubular system. They indicate that the fiber membrane along the surface is heterogeneous, not only with respect to the signs of its fixed charge sites, but also with respect to the sizes and relative permselectivities of these charged channels.

Animals↗
PubMed1964

SODIUM MOVEMENT ACROSS SINGLE PERFUSED PROXIMAL TUBULES OF RAT KIDNEYS.

Using perfusion techniques in single proximal tubule segments of rat kidney, the relationship between net sodium movement and active transport of ions, as measured by the short-circuit method, has been studied. In addition, the role of the colloid-osmotic pressure gradient in proximal transtubular fluid and sodium movement has been considered. Furthermore, the limiting concentration gradient against which sodium movement can occur and the relationship between intratubular sodium concentration and fluid transfer have been investigated. Comparison of the short-circuit current with the reabsorptive movement of sodium ions indicates that this process is largely, perhaps exclusively, active in nature. No measurable contribution of the normally existing colloid-osmotic pressure gradient to transtubular water movement was detected. On the other hand, fluid movement across the proximal tubular epithelium is dependent upon the transtubular sodium gradient and is abolished when a mean concentration difference of 50 mEq/liter is exceeded.

Biological Transport↗
PubMed1964

TRANSPORT OF SALT AND WATER IN RABBIT AND GUINEA PIG GALL BLADDER.

A simple and reproducible method has been developed for following fluid transport by an in vitro preparation of mammalian gall bladder, based upon weighing the organ at 5 minute intervals. Both guinea pig and rabbit gall bladders transport NaCl and water in isotonic proportions from lumen to serosa. In the rabbit bicarbonate stimulates transport, but there is no need for exogenous glucose. The transport rate is not affected by removal of potassium from the bathing solutions. Albumin causes a transient weight loss from the gall bladder wall, apparently by making the serosal smooth muscle fibers contract. Active NaCl transport can carry water against osmotic gradients of up to two atmospheres. Under passive conditions water may also move against its activity gradient in the presence of a permeating solute. The significance of water movement against osmotic gradients during active solute transport is discussed.

Absorption↗
PubMed1964

OSMOTIC PROPERTIES OF HUMAN RED CELLS.

The hematocrit method as a technique for determining red cell volume under anisotonic conditions has been reexamined and has been shown, with appropriate corrections for trapped plasma, to provide a true measure of cell volume. Cell volume changes in response to equilibration in anisotonic media were found to be much less than those predicted for an ideal osmometer; this anomalous behavior cannot be explained by solute leakage or by the changing osmotic coefficient of hemoglobin, but is quantitatively accounted for by the hypothesis that 20 per cent of intracellular water is bound to hemoglobin and is unavailable for participation in osmotic shifts.

Erythrocytes↗