Solute Transport Rate Research Articles

Proteoglycan Chemistry in Experimentally Injured Porcine Intervertebral Disk

An animal model of disk degeneration was used to study the concentration levels and types of proteoglycans in the different parts of the intervertebral disk. An annular incision was made with a scalpel blade into the anterior part of the porcine lumbar intervertebral disks via a retroperitoneal approach. Three months after injury the morphology of the injured disk had changed considerably. Disk height was diminished, and in the injured segment osteophytes had formed at the ventral edges of the vertebral body. The nucleus was small, fibrous, and yellowish. The annular lesion had healed by formation of granulation tissue, but the lamellar structure was partially destroyed. The concentration of inorganic [35S]sulfate had decreased across the whole disk, reflecting a decrease in the rate of solute transport. The concentration of incorporated [35S]sulfate had also decreased in the injured disks. The DNA concentration in the anterior annulus and in the nucleus had increased, whereas both the concentration of uronic acid and the ratio of chondroitin-6-sulfate to chondroitin-4-sulfate in the nucleus had decreased. Agarose gel electrophoresis combined with chondroitinase B digestion suggested the presence of dermatan sulfate proteoglycans in the injured annulus fibrosus. The morphology and chemical composition of the disks adjacent to the injured one were normal, and only a slight increase in the concentration of incorporated [35S]sulfate was observed in the disks above the injured one.

Rates of energy consumption and acquisition by lecithotrophic larvae of Bugula neritina (Bryozoa: Cheilostomata)

Lecithotrophic larvae of the cheilostome bryozoan, Bugula neritina (L.), lose metamorphic competence 12 to 24 h after release from the maternal zooid. The high respiration rate of newly released larvae (mean=306.3 pmol O2 larva-1 h-1, range=149.3 to 466.6, n=18 trials, 22.5°C) from adults collected at Link Port, Fort Pierce, Florida during the winter/spring of 1990–1991 reflects their active swimming behavior. The average energy content per larva was 15.24 mJ (range: 13.35 to 20.17 mJ ind-1, n=5 groups). If all cells have an identical energy content and metabolic rate, then 2 and 20% of the total energy content would be consumed by the onset (2 h post-release) and the loss (24 h post-release) of metamorphic competence. Larvae of B. neritina are a composite of both larval and juvenile tissues and the loss of metamorphic competence may be due to regional depletion of labile energy stores in transitory “larval” cells, particularly the ciliated cells that comprise the locomotory organ, the corona. Although “nonfeeding”, B. neritina larvae can acquire nutrients from the environment in the form of dissolved organic materials (DOM) in seawater. Both the amino acid alanine and the fatty acid palmitic acid can be transported from seawater ([S]=1 μM, 22.5°C). The rates of alanine influx (appearance of label in tissue) averaged 0.366 pmol larva-1 h-1 and, based on comparisons between rates of solute transport and metabolism, would contribute little (<1% of required energy) to offset the metabolic demand. The average rate of palmitic acid influx was 4.668 pmol larva-1 h-1 and assuming that the measured influx equals the net solute flux, could account for 21 to 72% of energy requirements. These data suggest that the duration of planktonic life of B. neritina larvae is principally regulated by the amount of endogenous energy stores, but may be modulated by available DOM in seawater.

Role of membrane trafficking in plasma membrane solute transport.

Cells can rapidly and reversibly alter solute transport rates by changing the kinetics of transport proteins resident within the plasma membrane. Most notably, this can be brought about by reversible phosphorylation of the transporter. An additional mechanism for acute regulation of plasma membrane transport rates is by the regulated exocytic insertion of transport proteins from intracellular vesicles into the plasma membrane and their subsequent regulated endocytic retrieval. Over the past few years, the number of transporters undergoing this regulated trafficking has increased dramatically, such that what was once an interesting translocation of a few transporters has now become a widespread modality for regulating plasma membrane solute permeabilities. The aim of this article is to review the models proposed for the regulated trafficking of transport proteins and what lines of evidence should be obtained to document regulated exocytic insertion and endocytic retrieval of transport proteins. We highlight four transporters, the insulin-responsive glucose transporter, the antidiuretic hormone-responsive water channel, the urinary bladder H(+)-ATPase, and the cystic fibrosis transmembrane conductance regulator Cl- channel, and discuss the various approaches taken to document their regulated trafficking. Finally, we discuss areas of uncertainty that remain to be investigated concerning the molecular mechanisms involved in regulating the trafficking of proteins.

Effect of solution environment on the permeability of red blood cells

The cell membrane permeability governs the rate of solute transport into and out of the cell, significantly affecting the cell's metabolic processes, viability, and potential usefulness in both biotechnological applications and physiological systems. Most previous studies of the cell membrane permeability have neglected the possible effects of suspending medium on membrane transport, even though there is extensive experimental evidence that suspending phase composition can significantly affect other properties related to the cell membrane (e.g., cell deformability, fragility, and aggregation rate). This study examined the effects of suspending phase composition (both proteins and electrolytes) on the permeability of human red blood cells to the metabolites creatinine and uric acid. Data were obtained using a stirred ultrafiltration device with direct cell- and proteinfree sampling through a semipermeable membrane. Both the uric acid and creatinine permeabilities were strongly affected by the suspending phase composition, with the permeabilities in different buffer solutions varying by as much as a factor of three. The predominant factors affecting the permeability were the presence (or absence) of chloride, phosphate/adenine, and proteins, although the magnitude and even the direction of these effects were significantly different for creatinine and uric acid transport. The dramatic differences in behavior for uric acid and creatinine reflect the different transport mechanisms for these solutes, with uric acid transported by a carrier-mediated mechanism and creatinine transported by passive diffusion through the lipid bilayer. These results provide important insights into the effects of solution environment on cell membrane transport and other cell membrane-mediated properties.

Urinary solute transport by ileal segments. I. Effects of nicotinic acid.

This study was conducted to quantify urinary solute transport by the ileum, using an in vivo human model, and to determine the effect of nicotinic acid on this process. Patients were studied under both basal conditions and niacin therapy. The rates of solute transport were established by analysis of excretion indexes for each solute. Potassium and ammonium were absorbed by the ileum, while phosphorus, sodium and bicarbonate were secreted. The percentage excretion index of sodium and bicarbonate increased by approximately 100 and 600% respectively, causing a significant rise in urinary pH. Although not statistically significant, there was a tendency for chloride to be absorbed and for water to pass into the bowel lumen. Nicotinic acid 3 g/day had no significant effect on urinary solute transport.

Field experiments in a fractured clay till: 2. Solute and colloid transport

A field tracer experiment was conducted in a lateral flow field in the weathered and highly fractured upper 6 m of a 40‐m‐thick clay‐rich till plain in southwestern Ontario. In the upper 3 m where fractures are closely spaced (&lt;0.13 m) the advancing front (C/C0 = 0.01) of the nonreactive solute tracers, bromide and 18O, migrated at rates of 0.01 to 0.07 m/d, over distances of 4 and 6 m and under a lateral hydraulic gradient of 0.24. In this same zone, two strains of colloid‐sized bacteriophage tracers migrated at rates of 2 to &gt;5 m/d. Simulations with a discrete fracture/porous matrix flow and transport model, which used the cubic law for flow in fractures, showed that diffusion of the solutes, but not the much larger colloids, into the matrix pore water between fractures is sufficient to cause the observed difference in solute and colloid transport rates. Transport‐derived and hydraulic conductivity‐derived fracture aperture values were similar, within a factor of 3 and falling mainly within a range of 5–40 μm. In the upper 3 m the solute tracers were evenly distributed between pore water in the fractures and the matrix, and as a result, solute transport can be closely approximated with an equivalent porous medium (EPM) approach. Below this depth, fractures are more widely spaced (0.13 to &gt;1 m) with concentration peaks tending to occur near visible fractures, and solute transport cannot be adequately described with an EPM approach.

Theoretical analysis of pore size distribution effects on membrane transport

The membrane selectivity can be critically affected by the pore size distribution. We examined the effect of different pore size distributions on the asymptotic membrane sieving coefficient, the hindered solute diffusivity, and the membrane hydraulic permeability by averaging the solute and solvent transport rates over specific pore size distributions. Although the calculated sieving coefficients and hindered diffusivities both increased significantly with an increase in the breadth of the distribution, the relationship between these two membrane transport parameters was relatively unaffected by the pore size distribution, allowing for reasonably accurate predictions of the hindered diffusivity from sieving data (or vice versa). These detailed calculations were also compared with predictions of a recently developed analytical model which implicitly accounts for the pore size distribution by evaluating the effective solute to pore size ratio using an expression for the solute partition coefficient in a random porous media. Model predictions were in good agreement with the detailed integral results for a membrane with a log-normal distribution with geometric standard deviation of around two, which is consistent with the observed pore size distribution for many ultrafiltration membranes. Model calculations also examined the effects of protein adsorption on membrane transport, with very different behavior seen for different adsorption mechanisms.

The place for cycler-assisted peritoneal dialysis in geriatric patients: comparison with hemodialysis

This study was designed to assess the place for cycler assisted peritoneal dialysis (CCPD) in the treatment of the elderly. The study population included 542 hemodialysis (HD) and 160 CCPD patients, including 206 HD and 60 CCPD patients older than 60 years of age. Physical activity (evaluated by the Karnofsky scale), risk of hospitalization, risk of death, subjective evaluation of health status (Nottingham Health Profile), peritonitis rate and peritoneal transport rates were evaluated. The incidence of peritonitis and solute transport rates among elderly and younger CCPD patients were similar. Physical activity scores were consistently lower among the elderly patients without differences between HD and CCPD. No apparent differences in the subjective assessment of physical health was seen between the elderly on HD and CCPD. Sixty percent of the elderly CCPD patients required partner assistance. The relative risk of hospitalization, risk of death and risk of discontinuation of therapy were higher for the elderly patients (p<0.05), without significant differences between HD and CCPD patients. No significant differences in the transfer rate to other therapy were seen between the elderly undergoing HD and CCPD.

Experimental evaluation of the influences of biogenic reworking on carbonate preservation in nearshore sediments

Laboratory experiments using two different species of marine infaunal deposit feeders have shown directly that macrofaunal activities influence sedimentary carbonate preservation. Feeding, burrowing and irrigation increase solute transport and solid phase reaction rates simultaneously, leading to more rapid carbonate dissolution than in sediments without fauna. These findings help to explain previously reported regular temporal fluctuations of foraminifera assemblages and spatial patterns of carbonate dissolution in nearshore deposits and represent one more example of how bioturbation accelerates elemental cycles in marine sediments.

The effect of anisotropic surface roughness on flow and transport in fractures

The topography of natural fracture surfaces has a strong influence on the flow and transport properties of fractures. In this paper we investigate the role of anisotropic surface roughness on fluid flow, solute transport, and electrical current flow in fractures. Our results show that the directional characteristics of the surfaces are more important in determining fracture transport properties than is the degree of roughness. Roughness oriented parallel to the primary flow direction substantially enhances fluid and solute transport rates through fractures, with the effect becoming more apparent as the amount of contact area between the surface increases. Roughness oriented transverse to the flow direction inhibits flow rates and delays the movement of solute through the fracture.

Visceral peritoneum is not essential for solute transport during peritoneal dialysis

The importance of visceral peritoneum in determining transperitoneal solute exchange was studied by determining the influence of evisceration on diffusive solute transport during peritoneal dialysis. Three series of experiments were performed in anesthetized New Zealand White rabbits. Series 1 studies compared solute transport rates from eviscerated rabbits (N = 5) with those from sham-operated controls (N = 5). Series 2 studies compared solute transport rates from eviscerated (N = 6) and sham-operated rabbits (N = 5) with application of circumferential abdominal compression to control intraperitoneal pressure and presumably maximize dialysate-peritoneum contact. Series 3 studies compared solute transport rates from sham-operated rabbits (N = 4) with and without applied circumferential abdominal compression. Transperitoneal solute exchange of creatinine and FITC-labeled neutral dextran (15 to 40 A) was equally assessed by both the dialysate to plasma concentration ratio at the end of the exchange and the diffusive permeability-area product of the peritoneum. Evisceration reduced creatinine (P less than 0.001) and dextran (15 to 30 A, P less than 0.05) transport to approximately one quarter that of controls in series 1 rabbits. When circumferential abdominal compression was applied in series 2 rabbits, however, evisceration had no effect on peritoneal solute transport rates. Moreover, circumferential abdominal compression per se had no effect on solute exchange in series 3 experiments. These findings demonstrate that the influence of evisceration on peritoneal solute transport depends on the experimental conditions. These observations further demonstrate that visceral peritoneum is not essential for solute transport during peritoneal dialysis.

Hydraulic response of highly compressible aquitards during consolidation

The transient hydraulic behavior of highly compressible aquitards is investigated through numerical analysis and field studies. Variations in the hydraulic parameters of an aquitard during consolidation are accounted for by incorporating empirical relationships derived from standard consolidation tests into the one‐dimensional flow equation. The resulting equation is highly nonlinear. The hydraulic response of an aquitard with physical properties typical of the compressible clays of Mexico City is evaluated with both standard linear analysis and with a nonlinear approach where the hydraulic parameters are stress‐dependent. The results indicate that decreases in the hydraulic diffusivity of the aquitard due to consolidation lead to diminished leakage flux, slower groundwater velocities and solute transport rates, longer transient response periods and less land subsidence than would be predicted by classical linear theory. Evaluation of field data from a site near Mexico City indicates that significant interpretive errors may arise if the stress dependence of the hydraulic parameters is ignored in these types of systems.

Flow-through particles for the high-performance liquid chromatographic separation of biomolecules: perfusion chromatography

This paper reports a new technique for reducing resistance to stagnant mobile phase mass transfer without sacrificing high adsorbent capacity or necessitating extremely high pressure operation. The technique involves the flow of liquid through a porous chromatographic particle, and has thus been termed “perfusion chromatography”. This is accomplished with 6000–8000 Å pores which transect the particle. Data from electron microscopy, column efficiency, frontal analysis and theoretical modelling all suggest that mobile phase will flow through these large pores. In this manner, solutes enter the interior of the particles through a combination of convective and diffusional transport, with convection dominating for Peclet numbers greater than one. The implications of flow through particles on bandspreading, resolution and dynamic loading capacity are examined. It is shown that the rate of solute transport is strongly coupled to mobile phase velocity such that bandspreading, resolution of proteins and dynamic loading capacity are unaffected by increases in mobile phase velocity up to several thousand centimeters per hour. The surface area of this very large-pore diameter material is enhanced by using a network of smaller, 500–1500 Å interconnecting pores between the throughpores. Scanning electron micrographs show that the pore network is continuous and that no point in the matrix is more than 5000–10 000 Å from a throughpore. As a consequence, diffusional path lengths are minimized and the large porous particles take on the transport characteristics of much smaller particles but with a fraction of the pressure drop. Capacity and resolution studies show that these materials bind and separate an amount of protein equivalent to that of conventional high-performance liquid chromatography as well as low performance agarose-based media at greater than 10–100 times higher mobile phase velocity with no loss in resolution.

Influence of cyclic loading on the nutrition of articular cartilage.

Articular cartilage is avascular. Nutrients are transported to the cells mainly by diffusion from the synovial fluid. Nutrient transport is also sometimes thought to be assisted by movement of fluid in and out of cartilage in response to cyclic loading of the tissue ('pumping'). The influence of pumping on transport of solutes through cartilage was measured by subjecting plugs of human femoral head cartilage immersed in medium containing radioactive solutes to a simulated walking cycle of 2.8 MPa at 1 Hz. The rate of absorption or desorption of tracers from the cycled plugs was compared with that of unloaded control plugs. For small solutes (urea, NaI) fluid transport did not affect the rate of solute transport significantly. Most major nutrients, such as glucose and oxygen, are small solutes and thus nutrition should not be affected by pumping. The rate of desorption of a large solute (serum albumin), however, was increased by 30-100% in plugs subjected to cyclic loading.

Urinary Solute Transport by Intestinal Segments: A Comparative Study of Ileum and Colon in Rats

This study was conducted to quantitate and compare urinary solute transport by ileum and colon in an in vivo rat model. Rates of solute transport were compared by analysis of rate constants for each experiment. Sodium and bicarbonate are secreted while ammonium and chloride are absorbed by both ileum and colon. Potassium is absorbed by ileum and not transported by colon. There is a tendency for water movement into the bowel lumen with both intestinal segments. Quantitatively, the amount of bicarbonate secretion and the increase in intraluminal pH is greater with ileum than colon. There is a net osmolar absorption from ileum but not colon. Hydrogen ion or ammonium absorption accounts for the majority and bicarbonate secretion the minority of the acid load in both ileum and colon. Ammonium appears to be absorbed either along with chloride or in exchange for sodium. (J. Urol, 143:1275-1279, 1990)

The impact of climate change on continuous corn production in the Southern U.S.A.

The Goddard Institute for Space Studies (GISS) General Circulation Model (GCM) has been used in conjunction with a field level plant process model (CERES-Maize) and a field level pesticide transport model (PRZM) to study the impacts of doubled levels of atmospheric CO2 on various aspects of corn production in the Southern U.S.A. Grid-box scale GCM output has been applied to a 38-year time series of historical weather data at 28 different locations for several typical soil profiles throughout the South. Limitations on the use of the climate scenario in conjunction with the process models are discussed. Major shortcomings include: 1) no direct impacts of atmospheric CO2 on plant growth and development in the plant process model; 2) neither macro-pore solute transport nor chemical decay rate response to temperature are included in the pesticide transport model; and 3) the climate change scenario output does not provide information concerning changes in temperature extremes and variability or precipitation frequency, intensity or duration. The latter are particularly critical parameters for the detailed simulation of hydrological processes. In spite of these omissions, the combination of the three models facilitates the study of the impacts of GCM modeled climate change on several inter-related agro-climatic issues of interest to agricultural policy makers. These issues include: changes in dryland and irrigated corn yields; changes in sowing and harvest dates; modification of crop water demand; and estimates of effects on pesticide losses from the soil surface and through leaching from the bottom of the active corn root zone. Model generated results which address these issues are presented but must be used with caution in light of the GCM and process model limitations. The results of this study suggest that substantial changes in agricultural production and management practices may be needed to respond to the climate changes expected to take place throughout the Southern U.S.A.

Long-term Increase in Peritoneal Membrane Transport Rates following Incidental Intraperitoneal Sodium Hypochlorite Infusion

A patient on continuous ambulatory peritoneal dialysis using an "O" set connection system with sodium hypochlorite as a disinfectant incidentally infused the disinfectant intraperitoneally on two occasions. The product of peritoneal membrane permeability and peritoneal membrane surface area increased after both infusions as judged by peritoneal equilibration test results and/or serum chemistries. Elevated peritoneal solute transport rates and reduced ultrafiltration gradually subsided but did not return to preinfusion values. This observation suggests that intraperitoneal sodium hypochlorite infusion may cause significant long-term alteration in peritoneal membrane transport characteristics.

Transport of major solutes and the relationship between solute concentrations and discharge in the Apure River, Venezuela

The Apure River is a major white-water tributary of the Orinoco River in Venezuela. The Apure is rich in solutes; its contribution to dissolved inorganic solids in the Orinoco (24%) is proportionately much greater than its contribution to discharge (6%). About 40% of the calcium and bicarbonate at the mouth of the Orinoco originate in the Apure drainage. The relationship between discharge and the concentrations of major solutes in the Apure was characterized with a two-compartment hyperbolic mixing model. Previous applications of the two-compartment model have been based on separate determinations of the model parameter β, which is a constant describing watershed hydrology, for each solute from data on concentrations. The use of a weighted mean β for all solutes is proposed as a means of assessing the importance of processes other than mixing. The model, when used on the Apure data, shows that a strong dilution effect prevails for sodium, calcium, magnesium, sulfate, and bicarbonate, and that a strong purging effect (increase of concentration with increasing discharge) is characteristic of soluble silicon. Biological immobilization of soluble silicon by diatoms during the season of low discharge is sufficiently large to account for the positive relationship between discharge and the concentration of soluble silicon. Specific transport rates of solutes from the basin are generally higher than global averages. In contrast, specific transport of chloride is low. Atmospheric sources control chloride transport in the Apure watershed; the low transport rates of chloride are probably explained by the great distance between the Apure watershed and the oceanic sources of atmospheric chloride.

The Time Course of Peritoneal Transport Kinetics in Continuous Ambulatory Peritoneal Dialysis Patients Who Develop Sclerosing Peritonitis

The time course of measurements of peritoneal solute transport in four continuous ambulatory peritoneal dialysis (CAPD) patients who developed sclerosing peritonitis is described. Loss of fluid removal capacity was found in all of them. In three, this loss was associated with an increase in peritoneal absorption of glucose from the dialysate and an increase in the transperitoneal transport rates of low-molecular-weight solutes and proteins. In the other patient a decrease in all these parameters was found. This seems to imply that the effective peritoneal surface area was increased in three patients and decreased in one. Peritoneal permeability to macromolecules remained unchanged as judged by the ratio between the clearance of IgG and albumin. Among the possible factors that contribute to the development of sclerosing peritonitis, some are likely to lead to a larger effective peritoneal surface area, like prostacyclin and the formation of new capillaries in poorly vascularized parts of the peritoneum. Others, such as extensive formation of collagen, could lead to a smaller effective surface area. Individual differences in susceptibility to these factors may lead to an increase or decrease in peritoneal solute transport rates. Follow-up measurements of peritoneal solute kinetics are necessary to identify those patients who are at risk.

Separation of Liquid Solutions by Contained Liquid Membranes

Abstract The technique of contained liquid membranes (CLM) for liquid solution separation is discussed. The CLM is obtained by confining the membrane liquid between two sets of microporous hollow fibers (MHF). The lumen of the hollow fiber carries the feed or the strip solution under proper phase pressure condition vis-a-vis the membrane phase. Various possible structural configurations of the CLM are illustrated with respect to the nature of microporous hollow fiber substrate, the feed solution and the liquid membrane. The contributions of different resistances to the solute transport rate are identified. Some basic experimental data obtained in small CLM permeators are presented for two systems with organic liquid membranes to illustrate how steady state separation is achieved after an initial unsteady period. The considerable advantages of the CLM structure over more traditional liquid membrane techniques such as supported liquid membrane (SLM) with respect to membrane stability, membrane regeneration ...