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PubMed2001

Kinetic analysis of boron transport in Chara.

The permeability of biological membranes to boric acid was investigated using the giant internodal cells of the charophyte alga Chara corallina (Klein ex Will. Esk. R.D. Wood). The advantage of this system is that it is possible to distinguish between membrane transport of boron (B) and complexing of B by plant cell walls. Influx of B was found to be rapid, with equilibrium between the intracellular and extracellular phases being established after approximately 24 h when the external concentration was 50 microM. The intracellular concentration at equilibrium was 55 microM, which is consistent with passive distribution of B across the membrane along with a small amount of internal complexation. Efflux of B occurred with a similar half-time to influx, approximately 3 h, which indicates that the intracellular B was not tightly complexed. The concentration dependence of short-term influx measured with 10B-enriched boric acid was biphasic. This was tentatively attributed to the operation of two separate transport systems, a facilitated system that saturates at 5 microM, and a linear component due to simple diffusion of B through the membrane. Vmax and Km for the facilitated transport system were 135 pmol m(-2) s(-1) and 2 microM, respectively. The permeability coefficient for boric acid in the Chara plasmalemma estimated from the slope of the linear influx component was 4.4 x 10(-7) cm s(-1) which is an order of magnitude lower than computed from the ether:water partition coefficient for B.

Biological Transport↗
PubMed1988

Alpha interferon accelerates lateral diffusion of Daudi cell surface differentiation antigens: measurement by fluorescence redistribution after photobleaching.

Lateral diffusion coefficients (D) of two surface differentiation antigens (sIgM and Bp35) were determined on interferon-sensitive (-IFs) or resistant (-IFr) Daudi cells by fluorescence photobleaching, using monospecific FITC-anti-IgM or PE-anti-Leu 16 probes. For untreated Daudi -IFs, mean (D) were 5.8 and 5.3 (x10(-10) cm2/sec). These increased, to 11 and 7.9 x 10(-10) cm2/sec (p less than 0.001) within 30 min after binding of recombinant IFN-a (80 to 800 U/10(6) cells), but decreased by up to 4-fold after Con A Mean (D) of identical surface antigens on Daudi-IFr were 8.2 and 9.4 x 10(-10) cm2/sec; and were not altered by IFN-a. Mean (D) of a lipid analog was up to 40-fold higher than for surface proteins and statistically identical in Daudi-IFs and Daudi-IFr. Rapid acceleration by IFN-a of surface protein lateral diffusion in Daudi-IFs obviously could facilitate anti-proliferative signal transduction; by contrast, a baseline increase of (D) in Daudi-IFr was evidently associated with their refractory state.

Antigens, CD20↗
PubMed2003

A diffusion-based theory of organism dispersal in heterogeneous populations.

We develop a general theory of organism movement in heterogeneous populations that can explain the leptokurtic movement distributions commonly measured in nature. We describe population heterogeneity in a state-structured framework, employing advection-diffusion as the fundamental movement process of individuals occupying different movement states. Our general analysis shows that population heterogeneity in movement behavior can be defined as the existence of different movement states and among-individual variability in the time individuals spend in these states. A presentation of moment-based metrics of movement illustrates the role of these attributes in general dispersal processes. We also present a special case of the general theory: a model population composed of individuals occupying one of two movement states with linear transitions, or exchange, between the two states. This two-state "exchange model" can be viewed as a correlated random walk and provides a generalization of the telegraph equation. By exploiting the main result of our general analysis, we characterize the exchange model by deriving moment-based metrics of its movement process and identifying an analytical representation of the model's time-dependent solution. Our results provide general and specific theoretical explanations for empirical patterns in organism movement; the results also provide conceptual and analytical bases for extending diffusion-based dispersal theory in several directions, thereby facilitating mechanistic links between individual behavior and spatial population dynamics.

Animal Migration↗
PubMed2006

Slow release of molecules in self-assembling peptide nanofiber scaffold.

Biological hydrogels consisting of self-assembling peptide nanofibers are potentially excellent materials for various controlled molecular release applications. The individual nanofiber consists of ionic self-complementary peptides with 16 amino acids (RADA16, Ac-RADARADARADARADA-CONH(2)) that are characterized by a stable beta-sheet structure and undergo self-assembly into hydrogels containing approximately 99.5% w/v water. We report here on the diffusion properties of phenol red, bromophenol blue, 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (pyranine, 3-PSA), 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (4-PSA), and Coomassie Brilliant Blue G-250 (CBBG) through RADA16 hydrogels. The apparent diffusivity (D ) of phenol red (1.05+/-0.08 x 10(-10) m(2) s(-1)) is higher than that of 3-PSA (0.050+/-0.004 x 10(-10) m(2) s(-1)) and 4-PSA (0.007+/-0.002 x 10(-10) m(2) s(-1)). The difference in 3-PSA and 4-PSA diffusivities suggests that the sulfonic acid groups directly facilitate electrostatic interactions with the RADA16 fiber surface. Bromophenol blue and CBBG were not released from the hydrogel, suggesting that they interact strongly with the peptide hydrogel scaffold. The diffusivities (D ) of the dyes decreased with increasing hydrogel peptide concentration, providing an alternate route of controlling release kinetics. These results indicate that release profiles can be tailored through controlling nanofiber-diffusant molecular level interactions.

Algorithms↗
PubMed1994

[Mechanisms of spinal block formation in Paget disease of bone. Radiographic study based on 14 cases].

Vertebral bridging occurs in approximately 10% of patients with spinal pagetic lesions. Diffuse idiopathic skeletal hyperostosis has been reported in patients with pagetic block vertebras and may facilitate vertebral fusion and extension of pagetic lesions. High prevalences of diffuse idiopathic skeletal hyperostosis have been found in patients with Paget's disease. To determine how pagetic block vertebras develop and to investigate relationships between Paget's disease and diffuse idiopathic skeletal hyperostosis, 244 patients with Paget's disease were studied retrospectively. Diagnostic criteria for diffuse idiopathic skeletal hyperostosis were the presence of flowing ossification along the anterolateral aspect of at least three contiguous vertebral bodies or presence of at least two anterolateral intervertebral bony bridges in the same spinal segment. Eight (33%) of the 244 patients had diffuse idiopathic skeletal hyperostosis. Two-thirds of patients with both conditions were male. There was no statistically significant association between presence of diffuse idiopathic skeletal hyperostosis and spinal involvement by Paget's disease. Fourteen pagetic block vertebras were identified in 11 male patients. Eight of these 11 patients had involvement of the fused vertebras or adjacent vertebras with diffuse idiopathic skeletal hyperostosis. Our findings confirm that diffuse idiopathic skeletal hyperostosis is common in patients with Paget's disease. The statistically significant association between diffuse idiopathic skeletal hyperostosis and pagetic vertebral fusion in the same site suggests that the former condition may be a risk factor for pagetic vertebral bridging.

Adult↗
PubMed1991

[Rediffusion system and cuff pressure of Brandt's endotracheal tube].

During anesthesia increase of the endotracheal cuff pressure might be caused by anesthetic gases used, especially nitrous oxide (N2O), which easily diffuses into the cuff. In 1983, Brandt developed a blocking system which is called Rediffusion System. The principle of Rediffusion System is to make use of an enlarged pilot balloon to facilitate the removal of nitrous oxide which has diffused into the cuff during anesthesia. This study was designed to test and verify the function of Brandt tube's Rediffusion System during anesthesia using nitrous oxide as an anesthetic. Twenty four patients (age 19-82 yr; ASA physical status I-III) who underwent surgery under general anesthesia were allocated into three groups. For endotracheal intubation, in group I (n = 11) and group II (n = 5), Mallinckrodt Brandt tubes respective of internal diameter (ID) = 7 mm and ID = 8 mm were used, and in group III (n = 8) Portex Blue-line tubes with ID = 7 mm was used. Anesthesia was maintained with N2O, isoflurane, and oxygen and the FiN2O was kept around 50%. The cuff pressure was measured at the intervals of 30 min for 3 h. There were no significant differences of initial cuff volumes between group I and group II, but the initial cuff volumes of Portex blue-line tube were significantly larger than Brandt tubes at desired pressure level. Cuff pressures increased as the duration of anesthesia lengthened in all types of endotracheal tubes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2004

Structural evolution of colloidal crystals with increasing ionic strength.

We have directly observed the structural evolution of colloidal crystals as a function of increasing ionic strength using confocal scanning laser microscopy. Silica colloids were sedimented onto a glass substrate in deionized water to create large, single domain crystals. The solution ionic strength was then increased by one of three methods of controlled electrolyte addition: (1) direct injection of electrolyte solutions, (2) single step diffusion of electrolyte solutions through a dialysis membrane, and (3) multiple step diffusion of electrolyte solutions of increasing ionic strength through a dialysis membrane. During direct injection of electrolyte solutions, initially large, single domain colloidal crystals were shear melted and then evolved into polycrystalline structures at low ionic strengths and gels at higher ionic strengths. Diffusion of electrolyte solutions though dialysis membranes in a single step produced gradient-driven transport that also melted initial single domain crystals to yield polycrystalline and gel structures similar to the injection approach. Interestingly, the multistep diffusion of several electrolyte solutions through dialysis membranes facilitated retention of large, single domain crystals even as particles came into adhesive contact. This was achieved by reducing the contraction rate of the crystalline lattice to allow sufficient time for diffusion-limited configurational rearrangements to occur within the evolving structure. These mechanically robust, single domain colloidal crystals may find important applications as templates for photonic materials and sensors.

Journal Article↗
PubMed1966

The steady-state transport of oxygen through hemoglobin solutions.

The steady-state transport of oxygen through hemoglobin solutions was studied to identify the mechanism of the diffusion augmentation observed at low oxygen tensions. A novel technique employing a platinum-silver oxygen electrode was developed to measure the effective diffusion coefficient of oxygen in steady-state transport. The measurements were made over a wider range of hemoglobin and oxygen concentrations than previously reported. Values of the Brownian motion diffusion coefficient of oxygen in hemoglobin solution were obtained as well as measurements of facilitated transport at low oxygen tensions. Transport rates up to ten times greater than ordinary diffusion rates were found. Predictions of oxygen flux were made assuming that the oxyhemoglobin transport coefficient was equal to the Brownian motion diffusivity which was measured in a separate set of experiments. The close correlation between prediction and experiment indicates that the diffusion of oxyhemoglobin is the mechanism by which steady-state oxygen transport is facilitated.

Chemical Phenomena↗
PubMed2004

Renal replacement therapy with high-cutoff hemofilters: Impact of convection and diffusion on cytokine clearances and protein status.

BACKGROUND: High-cutoff hemofilters are characterized by an increased effective pore size designed to facilitate the elimination of inflammatory mediators in sepsis. This study compares diffusive versus convective high-cutoff renal replacement therapy (RRT) in terms of cytokine clearance rates and effects on plasma protein levels. METHODS: Twenty-four patients with sepsis-induced acute renal failure were studied. A polyflux hemofilter with a cutoff point of approximately 60 kd was used for RRT. Patients were randomly allocated to either continuous venovenous hemofiltration (CVVH) with an ultrafiltration rate of 1 L/h (group 1) or 2.5 L/h (group 2) or continuous venovenous hemodialysis (CVVHD) with a dialysate flow rate of 1 L/h (group 3) or 2.5 L/h (group 4). Interleukin-1 (IL-1) receptor antagonist (IL-1ra), IL-1beta, IL-6, tumor necrosis factor-alpha (TNF-alpha), and plasma proteins were measured daily. RESULTS: CVVH achieved significantly greater IL-1ra clearance compared with CVVHD (P = 0.0003). No difference was found for IL-6 (P = 0.935). Increasing ultrafiltration volume or dialysate flow led to a highly significant increase in IL-1ra and IL-6 clearance rates (P < 0.00001). Peak clearances were 46 mL/min for IL-1ra and 51 mL/min for IL-6. TNF-alpha clearance was poor for both RRT modalities. A significant decline in plasma IL-1ra and IL-6 clearance was observed in patients with high baseline levels. Protein and albumin losses were greatest during the 2.5-L/h hemofiltration mode. CONCLUSION: High-cutoff RRT is a novel strategy to clear cytokines more effectively. Convection has an advantage over diffusion in the clearance capacity of IL-1ra, but is associated with greater plasma protein losses.

Adult↗
PubMed1996

Effect of fatty acids and the aqueous diffusion barrier on the uptake and transport of polychlorinated biphenyls in Caco-2 cells.

Polychlorinated biphenyls (PCBs) dissolved in dietary fat are absorbed in the gastrointestinal tract by the enterocytes in combination with the fatty acids proceeding from the lipid hydrolysis in the gut lumen. The effect of fatty acid absorption on the uptake and transport of 14 PCBs in enterocytes was studied using monolayers of the human intestinal Caco-2 cell line as a model system. The diffusive resistance of the unstirred water layer and the facilitating role of mixed bile salt micelles on the PCB uptake were examined by varying the thickness of the unstirred water layer adjacent to the apical membrane. In additional experiments, the polarity of the PCB uptake and transport in Caco-2 cells was determined. The solubility of PCBs in the mixed bile salt-fatty acid micelles was 2.7 to 4.8-fold higher than the solubility in plain bile salt micelles. Both the uptake and transport of PCBs in Caco-2 cells were significantly higher (up to 10-fold) when the PCBs were presented mixed with fatty acids. Reducing the thickness of the unstirred water layer resulted in an increased uptake of PCBs. The PCB uptake in Caco-2 cells exceeded the uptake as expected from monomer diffusion only, indicating that bile salt micelles facilitate the PCB transport over the unstirred water layer. Concentrations of dichlorobiphenyls accumulating in the basolateral medium stayed unexpectedly low, suggesting that Caco-2 cells might possess the capability of metabolizing lower chlorinated biphenyls. Uptake of PCBs into the Caco-2 cells was not significantly different whether the PCBs were presented at the apical side or at the basolateral side. However, transport of PCBs over the cell monolayer was significantly higher when the PCBs were presented at the apical side as compared to the basolateral side, suggesting that the unidirectional transport of lipids and lipoproteins affected the PCB transport as well. Our studies indicate that monolayers of the Caco-2 cell line offer a useful model system for studying the intestinal uptake and transport processes of hydrophobic xenobiotics such as polychlorinated biphenyls.

Biological Transport↗
PubMed2004

Quantification of water diffusion and relaxation times of human U87 tumors in a mouse model.

Assessing the potential of anti-cancer agents can be greatly facilitated by applying MRI methods to investigations with animal models. Quantitative diffusion imaging, T1, and T2 measurements may offer valuable information for understanding properties of the tumor and for evaluating new therapeutic approaches. The human U87 high-grade glial tumor is widely used for cancer investigations in orthotopic murine models. The physiological features of this model at the cellular and sub-cellular level have not, however, been well characterized by MRI. In this study, we measured the diffusion, T1 and T2 characteristics of water in the human U87 tumor at 8.5 T in an orthotopic murine model in vivo and analyzed their detailed changes in the transition from the tumor core through the tumor periphery, and out to surrounding tissue using custom developed radial profile analysis software. For the tumor bearing mice (n = 10), the mean average apparent diffusion coefficient (ADC) of the tumor core was 1.03 +/- 0.02 ( x 10(-3) mm2/s), while in the contralateral normal brain it was 0.73 +/- 0.03 ( x 10(-3) mm2/s). The mean T1 in tumor was 2.03 +/- 0.08 s and in normal brain tissue was 1.64 +/- 0.06 s. The mean T(2) in tumor was 0.062 +/- 0.002 s and in normal brain tissue was 0.048 +/- 0.001 s. The mean ADC, T1 and T2 of the tumor compared to normal tissue were significantly different (p < 0.005).

Animals↗
PubMed1998

An improved procedure for the preparation of X-ray diffraction-quality crystals of cytochrome p450cam.

A procedure for the crystallization of recombinant cytochrome P450cam has been developed which avoids the difficulties inherent in the glass-capillary free-interface diffusion method reported previously. The surface mutation, Cys334-->Ala (C334A), originally designed to prevent dimer formation and thus improve routine handling of the enzyme, facilitates crystallization by the hanging-drop vapour-diffusion technique. Crystals of (C334A)P450cam grow within 48 h and diffract to beyond 1.2 A at 100 K in-house on a Siemens multiwire area detector. Data have been collected from the camphor-bound form to 1.35 A.

Alanine↗
PubMed1994

Water transport across biological membranes.

The rate of the lateral diffusion of straight-chain phospholipids predicts the rate of water diffusion through bilayers. A new model of lipid dynamics integrates these processes. Substances such as cholesterol that reduce water diffusion proportionally reduce lateral diffusion. The model yields a number of predictions about the dynamics of the lipids at the Tm and suggests different mechanisms for how water diffuses across bilayers of other-than-straight-chain lipids, and how proteins bind to membranes. A second recent development in water transport across biological membranes is the discovery of a ubiquitous family of water transport proteins that facilitate large-volume water translocation. Like water diffusion through lipid bilayers, water transport by these proteins is directed by osmosis and is therefore under the control of ATP and ion pumps. The presence of water transport proteins in membranes is often regulated by hormones.

Biological Transport↗
PubMed2006

Reduced short latency afferent inhibition in diffuse axonal injury patients with memory impairment.

The present study used short interval intracortical inhibition (SICI), intracortical facilitation (ICF), and short latency afferent inhibition (SAI) to evaluate motor cortex excitability in 16 diffuse axonal injury (DAI) patients with memory impairment and compared the data with those of 16 healthy controls. SAI was reduced in patients compared with controls (92+/-12 versus 39+/-11% of the test size; p<0.0001, unpaired t-test). DAI patients tended to have a high resting motor threshold (RMT) and less pronounced SICI and ICF than controls, but these differences were not significant. A single oral dose (3mg) of donepezil, an acetylcholinesterase inhibitor that is commonly used to treat Alzheimer's disease (AD), improved SAI in DAI patients with wide individual variations that ranged from an increase of 77-18% of test size. These findings suggest that measuring SAI may provide a means of probing the integrity of cholinergic networks in an injured human brain.

Adult↗
PubMed1987

The effect of myoglobin-facilitated oxygen transport on the basal metabolism of papillary muscle.

A mathematical model of oxygen diffusion into cylindrical papillary muscles is presented. The model partitions total oxygen flux into its simple and myoglobin-facilitated components. The model includes variable sigmoidal, exponential, or hyperbolic functions relating oxygen partial pressure to both fractional myoglobin saturation and rate of oxygen consumption. The behavior of the model was explored for a variety of saturation- and consumption-concentration relations. Facilitation of oxygen transport by myoglobin was considerable as indexed both by the elevation of oxygen partial pressure on the longitudinal axis of the muscle and by the fraction of total oxygen flux at the muscle center contributed by oxymyoglobin. Despite its facilitation of oxygen flux at the muscle center, myoglobin made only a negligible contribution to the total oxygen consumption averaged over the muscle cross-section. Hence the presence of myoglobin fails to explain either the experimentally determined basal metabolism-muscle radius relation or the stretch effect observed in isolated papillary muscle.

Animals↗
PubMed2006

Passive and facilitated transport in nuclear pore complexes is largely uncoupled.

Nuclear pore complexes provide the sole gateway for the exchange of material between nucleus and cytoplasm of interphase eukaryotic cells. They support two modes of transport: passive diffusion of ions, metabolites, and intermediate-sized macromolecules and facilitated, receptor-mediated translocation of proteins, RNA, and ribonucleoprotein complexes. It is generally assumed that both modes of transport occur through a single diffusion channel located within the central pore of the nuclear pore complex. To test this hypothesis, we studied the mutual effects between transporting molecules utilizing either the same or different modes of translocation. We find that the two modes of transport do not interfere with each other, but molecules utilizing a particular mode of transport do hinder motion of others utilizing the same pathway. We therefore conclude that the two modes of transport are largely segregated.

Active Transport, Cell Nucleus↗
PubMed1988

Synergism at central synapses due to lateral diffusion of transmitter.

Recordings of inhibitory postsynaptic currents in the goldfish (Carassius auratus) Mauthner cell demonstrate nonlinear interactions when adjacent synapses are coactivated. Responses evoked by single presynaptic neurons were paired with those due to activation of a limited pool of similar inhibitory cells. In about 50% of the experiments the compound currents were substantially larger than the sum of their individual components. Potentiation was maximal when the two responses occurred nearly simultaneously, and its decay paralleled that of the conditioning current; it started with a delay of about 300 microsec, and calculations indicate that in this time transmitter molecules would diffuse laterally 0.5-1.1 micron, which equals the separation of adjacent synapses. Iontophoretically applied glycine produced a comparable enhancement of the eighth nerve evoked inhibitory current. When quantal inhibitory responses were simulated, taking into consideration glycine diffusion, transmitter-receptor interactions, and channel activation, with the latter requiring two binding steps, the results demonstrated that the facilitation when neighboring inputs are active is due to lateral diffusion of the transmitter, glycine, to fringe areas where single bound receptors are available for further interactions and channel opening.

Animals↗
PubMed1999

Glial swelling and astrogliosis produce diffusion barriers in the rat spinal cord.

Cell swelling and astrogliosis (manifested as an increase in GFAP) were evoked in isolated rat spinal cords of 4-21-day-old rats by incubation in either 50 mM K+ or hypotonic solution (235 mosmol kg(-1)). Application of K+ and hypotonic solution resulted at first in a decrease of extracellular space (ECS) volume fraction alpha (ECS volume/total tissue volume) and an increase in tortuosity lambda (lambda2 = free/apparent diffusion coefficient) in spinal gray (GM) and white matter (WM). These changes resulted from cell swelling, since the total water content (TW) in spinal cord was unchanged and the changes were blocked in Cl- -free solution and slowed down by furosemide and bumetanide. Diffusion in WM was anisotropic, i.e., more facilitated along fibers (x-axis) than across them (y- or z-axis). The increase of lambda(y,z) was greater than that of lambda(x), reaching unusually high values above 2.4. In GM only, during continuous 45 min application, alpha and lambda started to return towards control values, apparently due to cell shrinkage of previously swollen cells since TW remained unchanged. This return was blocked by fluoroacetate, suggesting that most of the changes were due to the swelling of glia. A 45 min application of 50 mM K+ and, to a lesser degree, of hypotonic solution evoked astrogliosis, which persisted after washing out these solutions with physiological saline. During astrogliosis lambda increased again to values as high as 2.0, while alpha either returned to or increased above control values. This persistent increase in lambda after washout was also found in WM, and, in addition, the typical diffusion anisotropy was diminished. Our data show that glial swelling and astrogliosis are associated with a persistent increase in ECS diffusion barriers. This could lead to the impairment of the diffusion of neuroactive substances, extrasynaptic transmission, "crosstalk" between synapses and neuron-glia communication.

Animals↗