Osmotic Shifts Research Articles

Activation of extracellular signal-regulated kinases Erk-1 and Erk-2 by cell swelling in H4IIE hepatoma cells.

Hepatic metabolism and gene expression are among the factors controlled by the cellular hydration state, which changes within minutes in response to aniso-osmotic environments, cumulative substrate uptake, oxidative stress and under the influence of hormones such as insulin. The signalling events coupling cell-volume changes to altered cell function were studied in H4IIE rat hepatoma cells. Hypo-osmotic cell swelling resulted within 1 min in a tyrosine kinase-mediated activation of the extracellular signal-regulated protein kinases Erk-1 and Erk-2, which was independent of protein kinase C and cytosolic calcium. Activation of mitogen-activated protein kinases was followed by an increased phosphorylation of c-Jun, which may explain our recently reported finding of an about 5-fold increase in c-jun mRNA level in response to cell swelling. Pretreatment of cells with pertussis or cholera toxin abolished the swelling-induced activation of Erk-1 and Erk-2, suggesting the involvement of G-proteins. Thus, a signal-transduction pathway resembling growth factor signalling is activated already by osmotic water shifts across the plasma membrane, thereby providing a new perspective for adaption of cell function to alterations of the environment.

Regulation of metabolism by changes in cellular hydration

Besides his pioneering work in the development and use of fat emulsions in parenteral nutrition, Arvid Wretlind's interest also resided in protein and amino acid metabolism. He was among the first to demonstrate that in animals growth could be achieved by using synthetic amino acids instead of dietary protein. Here, amino acids not only serve as important building blocks for protein synthesis; their growthpromoting and anabolic role is also related to the topic discussed in this article, namely the regulation of cell function by the cellular hydration state. Within the last few years, it has become clear that cellular hydration is rather dynamic and can change within minutes under the influence of hormones, nutrient supply and oxidative stress. Most importantly, such a short-term modulation of cell volume within a narrow range, acts per se as a potent signal which modifies cellular metabolism and gene expression (for reviews see (13)). In fact, cell swelling due to osmotic water shifts into the cell acts as an anabolic signal. We are still at the beginning of the understanding of this novel and important mechanism of metabolic control. Alterations of cellular hydration under the influence of glutamine are at least one major mechanism underlying the anabolic effects of glutamine. Meanwhile evidence is accumulating that disturbances of cellular hydration may be important in the understanding of a variety of clinical conditions such as protein-catabolic states (4), cholestasis (5), viral infection (6) and hepatic encephalopathy (7). Only a few aspects will be adressed in this article. The interaction between cellular hydration and cell function was most extensively studied in liver cells, but evidence is increasing that modulation of cell function in response to alterations of cellular hydration is a general mechanism. Factors modulating cellular hydration

Development and critical evaluation of an improved comprehensive multicompartment model for the exchange processes during hemodialysis.

An improved comprehensive multicompartment model for the simulation of the most important metabolic state variables in the patient during dialysis is presented. With this approach time courses of urea, creatinine, K+, Na+, Cl-, HCO3-, H+ and CO2 can be predicted. Additionally, osmotic water shifts as well as resting membrane potentials are calculated. The model contains the following extensions compared to classical approaches: For the calculation of osmotic water shifts, not only sodium, but also urea, potassium, chloride and unspecified indiffusable ions are taken into account. Furthermore, hemodynamic aspects are considered by assuming two tissue groups with different perfusion. Thus it is possible to estimate the influence of hemodynamic parameters (e.g. cardiac output or blood flow distribution) on the exchange processes. The model can be adjusted individually by several system parameters. This adjustment is performed by minimizing the sum of the quadratic differences between simulated and measured plasma concentrations of the considered substances. A first validation has been performed successfully with measured data from 18 dialysis patients. After the effective whole-body exchange area of the resting cell membranes for potassium, sodium and chloride had been estimated, rebound effects for those electrolytes could be simulated successfully.

Monopolar cell axons in the first optic neuropil of the housefly, Musca domestica L., undergo daily fluctuations in diameter that have a circadian basis

Two types of monopolar cell interneurons, each with a single representative in every unit cartridge of the first optic neuropil, or lamina, of the housefly's optic lobe, have axons that undergo cyclical changes in diameter. The axons are largest during the beginning of day in a normal LD light cycle and smallest during the middle of the night, changes that were however significant only for one of the cells (L2). The axon cross-sectional area and its cyclical change for both L1 and L2 were both larger in the proximal lamina. The changes are not a simple consequence of relative osmotic change. Dehydration paradoxically increases axon size, and also fails to alter the day/night rhythm of axon size changes. Under conditions of constant darkness, both axons decrease in size, and one of the cells (L2) retains its cyclical size changes, being larger in the subjective day than in the subjective night. Under conditions of constant light, both axons increase in size, and L2 again shows a cyclical size change, just as under conditions of constant darkness. These changes seen under constant conditions are, by definition, circadian in origin. The effects of exposure to light or darkness can partially reset these circadian changes. One extra hour of light during the day increases the size of L1 and L2, whereas 1 hr of extra dark during the night does not decrease their size. It takes 13 hr of light to reverse the rhythm in size. The mechanism for all these changes is unclear but may involve ionic fluxes, possibly that are secondary to osmotic shifts and probably that involve at least two independent processes.

The use of epi-fluorescence to determine the viability of Saccharomyces cerevisiae subjected to osmotic shifts

The viability of yeast cells subjected to osmotic shifts was determined using an epi-fluorescence method in conjunction with an image analysis system. This technique provided an accurate and rapid measurement of viability and results were found to correlate closely with the colony-forming unit (CFU) method when used under the same conditions. In addition, the epi-fluorescence method proved to be more versatile in that viability measurements could actually be carried out at low water activities ( a w), whereas the reference CFU method required an increase in a w.

Immunofluorescence localization of the unconventional myosin, Myo2p, and the putative kinesin-related protein, Smy1p, to the same regions of polarized growth in Saccharomyces cerevisiae.

Myo2 protein (Myo2p), an unconventional myosin in the budding yeast Saccharomyces cerevisiae, has been implicated in polarized growth and secretion by studies of the temperature-sensitive myo2-66 mutant. Overexpression of Smy1p, which by sequence is a kinesin-related protein, can partially compensate for defects in the myo2 mutant (Lillie, S. H. and S. S. Brown, 1992. Nature (Lond.). 356:358-361). We have now immunolocalized Smy1p and Myo2p. Both are concentrated in regions of active growth, as caps at incipient bud sites and on small buds, at the mother-bud neck just before cell separation, and in mating cells as caps on shmoo tips and at the fusion bridge of zygotes. Double labeling of cells with either Myo2p or Smy1p antibody plus phalloidin was used to compare the localization of Smy1p and Myo2p to actin, and by extrapolation, to each other. These studies confirmed that Myo2p and Smy1p colocalize, and are concentrated in the same general regions of the cell as actin spots. However, neither colocalizes with actin. We noted a correlation in the behavior of Myo2p, Smy1p, and actin, but not microtubules, under a number of circumstances. In cdc4 and cdc11 mutants, which produce multiple buds, Myo2p and Smy1p caps were found only in the subset of buds that had accumulations of actin. Mutations in actin or secretory genes perturb actin, Smy1p and Myo2p localization. The rearrangements of Myo2p and Smy1p correlate temporally with those of actin spots during the cell cycle, and upon temperature and osmotic shift. In contrast, microtubules are not grossly affected by these perturbations. Although wild-type Myo2p localization does not require Smy1p, Myo2p staining is brighter when SMY1 is overexpressed. The myo2 mutant, when shifted to restrictive temperature, shows a permanent loss in Myo2p localization and actin polarization, both of which can be restored by SMY1 overexpression. However, the lethality of MYO2 deletion is not overcome by SMY1 overexpression. We noted that the myo2 mutant can recover from osmotic shift (unlike actin mutants; Novick, P., and D. Botstein. 1985. Cell. 40:405-416). We have also determined that the myo2-66 allele encodes a Lys instead of a Glu at position 511, which lies at an actin-binding face in the motor domain.

Sensitivity of spores and growing cells ofBacillus thuringiensis varisraeliensis andBacillus sphaericus to osmotic variations

EntomopathogenicBacillus thuringiensis var.israelensis (Bti) andBacillus sphaericus (Bf) strains species were studied in relation to their capacity to resist osmotic and nutritional shifts. Their behavior was compared with other bacilli,B. subtilis (Bs) andB. megaterium (Bm). In contrast to these reference strains, vegetative cultures of both species presented a dramatic sensitivity to hyperosmotic shock, independent of the growth period assayed. Subjected to an osmotic and nutritional shift-down (one hundredth dilution in water), Bti cultures resisted it, divided, and sporulated, as did Bm strains, whereas Bf and Bs cultures lysed or died. Spores from these toxic species were of less quality regarding resistance to heat or osmotic strength; but a nontoxic Bti derivative produced spores of better quality. Spore germination was also followed in these strains. The poor spore quality of these species correlated well with their poor survival in field experiments.

A new visualization chamber to study the transient volumetric response of yeast cells submitted to osmotic shifts

A visualization chamber has been developed to analyze potential correlations between osmotic step increase on yeasts and the resultant cell volume decreases. Image analysis was used to characterize the step increases in the center of the chamber and to measure the changes in the cell volume. Step increases of different intensities have been performed on the yeast Saccharomyces cerevisiae. This device has allowed the kinetics of the volumetric evolution of the cells to be observed. The water exit flow rate from the cell was found to occur in the first 10 s following the hypertonic step change. Comparison of the time constants of the chamber and of the cell volume variations allowed to conclude that the time constant of the water transfer across the membrane was short (about 1 s).

Yeast resistance to high levels of osmotic pressure: Influence of kinetics

Application of slow and progressive changes in osmotic pressure to cells of S. cerevisiae allowed the preservation of viability up to very high levels of osmotic pressure (125 MPa). Viability was examined in relation to water exit from the cell in terms of cell volume changes which were measured continuously using an on-line image analysis system. It has been shown that the high survival level of cells subjected to such progressive changes in osmotic pressure are due to physical factors alone and mainly to the water flow rate during the period just after the osmotic shift.

The therapeutic use of albumin

In this review, we condense and summarize the results of studies on the therapeutic use of human albumin to promote the more efficient use of this costly resource. Reports of major controlled and uncontrolled therapeutic trials, reviews, and summary articles published in English between 1972 and 1991 were identified through library and MEDLINE searches. Case series, prospective studies, and blinded therapeutic trials were identified from the bibliographies of these sources. All sources were critically evaluated for information about the comparative physiologic results and patient outcomes of the therapeutic use of albumin solutions, crystalloid solutions, and volume expanders other than albumin. The therapeutic use of albumin is of marginal benefit for many conditions for which it has been administered, apparently because of the body's capacity to quickly compensate for rapid colloid osmotic shifts. Human studies show little or no demonstrable value for albumin when it is administered for nutritional supplementation, wound healing, perioperative fluid replacement, treatment of early thermal injury, or therapy during extensive retroperitoneal surgery (including aortic aneurysm resection). Therapeutic albumin has well-defined value in several special circumstances: large-volume paracentesis in cirrhotic patients, acute nephrotic syndromes with diuretic resistance, organ transplantation, and plasmapheresis. Additional studies are needed to compare the efficacy of albumin with other volume expanders. For most purposes, balanced crystalloid solutions are satisfactory substitutes for colloid volume expanders and can be obtained at a fraction of the cost of colloid volume expanders.

Osmotic effects on the CA1 neuronal population in hippocampal slices with special reference to glucose.

1. Lowered osmolality promotes epileptiform activity both clinically and in the hippocampal slice preparation, but it is unclear how neurons are excited. We studied the effects of altered osmolality on the electrophysiological properties of CA1 pyramidal cells in hippocampal slices by the use of field and intracellular recordings. The excitability of these neurons under various osmotic conditions was gauged by population spike (PS) amplitude, single cell properties, and evoked synaptic input. 2. The orthodromic PS recorded in stratum pyramidale and the field excitatory postsynaptic potential (EPSP) in stratum radiatum were inversely proportional in amplitude to the artificial cerebrospinal fluid (ACSF) osmolality over a range of +/- 80 milliosmoles/kgH2O (mosM). The effect was osmotic because changes occurred within the time frame expected for cellular expansion or shrinkage and because permeable substances such as dimethyl sulfoxide or glycerol were without effect. Dilutional changes in ACSF constituents were experimentally ruled out as promoting excitability. 3. To test whether the field data resulted from a change in single-cell excitability, CA1 cells were intracellularly recorded during exposure to +/- 40 mosM ACSF over 15 min. There was no consistent effect upon CA1 resting potential, cell input resistance, or action potential threshold. 4. Osmotic alteration of orthodromic and antidromic field potentials might involve a change in axonal excitability. However, the evoked afferent volley recorded in CA1 stratum pyramidale or radiatum, which represents the compound action potential (CAP) generated in presynaptic axons, remained osmotically unresponsive with regard to amplitude, duration, or latency. This was also characteristic of CAPs evoked in isolated sciatic and vagus nerve preparations exposed to +/- 80 mosM. Therefore axonal excitability and associated extracellular current flow generated periaxonally are not significantly affected by osmotic shifts. 5. The osmotic effect on field potential amplitudes appeared to be independent of synaptic transmission because the inverse relationship with osmolality held for the antidromically evoked PS. Moreover, as recorded with respect to ground, the intracellular EPSP-inhibitory postsynaptic potential (IPSP) sequence (evoked from CA3 stratum radiatum) was not altered by osmolality. 6. The PS could occasionally be recorded intracellularly as a brief negativity interrupting the evoked EPSP. In hyposmotic ACSF, the amplitude increased and action potentials arose from the trough of the negativity as expected for a field effect. This is presumably the result of enhanced intracellular channeling of current caused by the increased extracellular resistance that accompanies cellular swelling.(ABSTRACT TRUNCATED AT 400 WORDS)

Hema and latex: a dangerous combination?

The endovascular treatment of intracranial aneurysms with detachable balloons requires filling materials that harden reliably and are compatible with the balloon. While the incompatibility of latex balloons and hema from different manufacturers is known, no incompatibility has been assumed thus far if both balloon and hema were from the same manufacturer. In two series of experiments, we filled a total of 20 latex balloons with hema as recommended by the balloon manufacturer. Within an observation time of 4 weeks all latex balloons ruptured. At the time of rupture, the balloons had gained 5-10% in weight, most likely due to osmotic shifts in water. Simultaneously, hardening of the hema resulted in a loss of elasticity of the latex. Until these compatibility problems are solved, silicone rather than latex balloons should be used with permanent filling materials such as hema for the endovascular treatment of intracranial aneurysms.

Haematological disturbances and osmotic shifts in rainbow trout, Oncorhynchus mykiss (Walbaum) under acid and aluminium exposure

Elevated values of haematocrit were observed in rainbow trout (Oncorhynchus mykiss) during combined acid and aluminium exposure. Possible causes of this, i.e., decreased plasma volume, swelling of erythrocytes, and/or mobilization of erythrocytes into the blood were investigated. Slight haematocrit increases (10–20%) during mild acid stress (pH 5.0, 25 μmol Ca2+·1-1) were mostly caused by osmotic shifts. Both swelling of erythrocytes rocytes and a significant decrease of the plasma volume were demonstrated in fish at pH 5.0. These osmotic disturbined were greater during acid exposure (pH 5.0) combined with Al (60 μg·1-1; 200 μg·1-1). In addition, numbers of erythrocytes increased by 40% compared to acid exposure, which contributed to the severe haematocrit rise (35%) during Al exposure. A contraction of the spleen releasing erythrocytes into the blood is suggested to occur as an adrenergic response to hypoxia, which is observed in fish acutely exposed to Al.

Studies on the pathogenesis of the early dumping syndrome induced by intraduodenal instillation of hypertonic glucose.

A reaction indistinguishable from the early dumping syndrome was induced in four of nine normal volunteers by intraduodenal instillation of a hypertonic glucose meal. Tachycardia and marked peripheral vasodilatation were demonstrated in 'dumpers' by Doppler ultrasound measurements of the arterial blood flow signal. The dumping reaction was not detectably altered by the addition of guar to the meal. Plasma VIP concentration rose and plasma volume fell to a similar degree in 'dumpers' and 'non-dumpers', suggesting that neither event is an integral component of the dumping mechanism. In contrast, the rates of rise of blood glucose and enteroglucagon concentration were markedly greater in 'dumpers'. The results are inconsistent with the conventional explanation that the early dumping syndrome is caused by a large osmotic fluid shift, but are compatible with a mechanism involving an initial period of intestinal hypermotility.

Factors Which Affect Cardiac Performance during Hemodialysis

SummaryCardiac performance during hemodialysis is dependent on preexisting conditions (i.e., coronary artery disease, myocardial hypertrophy, LV compliance, anemia, hypertension, etc.) and the hemodynamic alterations caused by the dialysis procedure itself (osmotic shifts, ionized calcium changes, etc.). Clinical hemodynamic investigations of cardiac performance during uremia have been hampered by the difficulty in isolating individual parameters of ventricular function. Myocardial reserve in dialysis patients is often reduced because of antecedent ischemic disease, hypertension, and the presence of autonomic dysfunction in many patients. Rapid volume losses or gains are likely to be less well tolerated with resultant hypotensive syndromes or pulmonary edema as the result. The controlled volume loss achievable with newer dialysis machines, the use of higher dialysate sodium concentrations, and the wider availability of erythropoietin may improve the tolerance to the procedure for many patients.

The measurement of blood density and its meaning.

Density is defined as mass per unit volume. The classical technique to measure the density of fluids consists of a determination of mass and volume. Blood density is proportional to hematocrit or, more exactly, to the total protein concentration of blood; only to a minor extent is blood density influenced by other plasma solutes. Since the introduction of the mechanical oscillator technique for the continuous recording of fluid density a sizeable amount of experience has accumulated. This review summarizes recent work performed with this technique. It appears that the scientific interest in a variable like blood density depends on the availability of a suitable and simple method. Until the oscillator technique was available the measurement of density was too complicated or too inaccurate for routine laboratory use. A further new technique permits us to determine fluid densities by measuring sound velocity transmission. The density dilution method can be used for the determination of distribution volumes, of flow through organs, and of the cardiac output. The influence of temperature and of certain artifacts like acceleration forces in the density measuring device have to be considered any may be used for additional diagnostic purposes like determination of erythrocyte sedimentation velocity. The new technique opens a reasonable simple way to study fluid shift between interstitial space and capillaries. The arterio-venous density gradient in an organ depends on the lymph production. The injection of a hypertonic solution leads to an osmotic fluid shift from the extravascular space towards the blood. This fluid shift can be recognized by a reduction of the blood density. A simple model for the description of this reaction is presented.

Central pontine myelinolysis in severely burned patients: relationship to serum hyperosmolality.

The rapid correction or over-correction of hyponatremia is believed by many to be the crucial factor in the causation of central pontine myelinolysis (CPM). Over a 17-year period we found CPM in 10 (7%) of the 139 burn patients examined postmortem but in only 10 (0.28%) of the 3,528 patients in the general autopsy population (p less than 0.001). Each of the burn patients with CPM had suffered a prolonged, nonterminal episode of extreme serum hyperosmolality, whereas most burn patients without CPM had not suffered such an episode. The histologic age of the lesions correlated with the duration of time between the hyperosmolar episode and death. Hypernatremia, hyperglycemia, and azotemia, alone or combined, accounted for the hyperosmolality. No single electrolyte or metabolic derangement was essential, as in at least one burn patient with CPM the serum sodium, glucose, or blood urea nitrogen was normal during the hyperosmolar episode. Hyponatremia was not present in any burn patient with CPM. We conclude that severely burned patients, like alcoholics, are especially susceptible to CPM, and that in burn patients with CPM there is a striking association with serum hyperosmolality. The data also suggest that the rapid correction of hyponatremia exerts its effects by causing an osmotic shift and not because of any specific property of the sodium ion.

Measurement of live bacteria by Nomarski interference microscopy and stereologic methods as tested with macroscopic rod-shaped models.

A new method is proposed to measure bacterial cells under growth conditions. Bacterial cells, suspended in their growth medium, were attached to a cover slip with poly-L-lysine. The cover slip was inverted and placed on a glass microscope slide. To prevent dehydration of the medium, the edges of the cover slip were sealed to the microscope slide with clear fingernail polish. The bacteria on the slide were then quickly photographed with a Leitz light microscope, using Nomarski optics. The photographic negatives were then projected at a standard distance through a lens system, and the projected images of the whole cells were outlined by hand onto graph paper. The profile images so transcribed onto the graph paper were in effect transverse sections of each of the cells. Using stereologic grid and point counting techniques, the area of the cell transverse section as well as the perimeter or circumference of the transverse section were estimated. Formulae were developed so that both the volume and surface area of the whole cell could be ascertained from these area and circumference measurements. Since the efficacy of any measurements of surface area and volume of microscopic rod-shaped bacterial cells could be questioned, macroscopic rod-shaped models were used to test the theory and formulae and to compare this method with other commonly used cell-sizing techniques. This technique could be used in any study of bacterial cell size or changes in cell size (e.g., osmotic shifts).

Osmotic adaptation of T4 infectedEscherichia coli

In contrast to enzymatic adaptation, osmotic adaption is possible with T4-infected Escherichia coli B cells. After an osmotic shift from 220 mOsM to 690 mOsM the intracellular content of potassium rises in infected cells as well as in uninfected cells. After osmotic shock the involved TrKA transport system shows an increased discrimination against rubidium (Rb+) and for potassium (K+).

Osmotic adaptation of T4 infected Escherichia coli

In contrast to enzymatic adaptation, osmotic adaption is possible with T4-infected Escherichia coli B cells. After an osmotic shift from 220 mOsM to 690 mOsM the intracellular content of potassium rises in infected cells as well as in uninfected cells. After osmotic shock the involved TrKA transport system shows an increased discrimination against rubidium (Rb+) and for potassium (K+).