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PubMed1985

Pig gastric mucus: a one-way barrier for H+.

Gastric mucus is thought to protect the underlying mucosal cells from mechanical hazards and back-diffusion of luminal H+. In health, a pH gradient exists across the mucus layer from the variable low pH of the lumen to a pH approaching neutrality at the epithelial cell surface. By current hypotheses this gradient is maintained by the combined effects of an unstirred layer, restricted or slowed diffusion of H+ in the mucus, and the epithelial cell secretion of bicarbonate, which is confined to the cell surface by the mucus layer. These mechanisms do not explain how H+ is secreted through mucus in the first place. Using a modified diffusion chamber we have shown that pig gastric mucus facilitates a low-efficiency Na+/H+ exchange--a property that helps to clarify some previously unexplained components of H+ secretion. When a solution containing Na+ was separated by a layer of fresh pig gastric mucus from a solution of similar pH containing a much lower concentration of sodium, the sodium-rich solution was electrically negative relative to the sodium-poor solution and its pH decreased significantly with time. A similar pH gradient developed when the barrier was a synthetic cation-exchange membrane, and one of opposite sign when it was an anion exchanger; no pH gradient developed across neutral barriers. It is suggested that similar electrical coupling of H+ diffusion to active Na+ transport might in vivo ensure that secreted H+ moves into the gastric lumen.

Animals↗
PubMed2006

76-space analysis of grey matter diffusivity: methods and applications.

Diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) allow in vivo investigation of molecular motion of tissue water at a microscopic level in cerebral gray matter (GM) and white matter (WM). DWI/DTI measure of water diffusion has been proven to be invaluable for the study of many neurodegenerative diseases (e.g., Alzheimer's disease and Creutzfeldt-Jakob disease) that predominantly involve GM. Thus, quantitative analysis of GM diffusivity is of scientific interest and is promised to have a clinical impact on the investigation of normal brain aging and neuropathology. In this paper, we propose an automated framework for analysis of GM diffusivity in 76 standard anatomic subdivisions of gray matter to facilitate studies of neurodegenerative and other gray matter neurological diseases. The computational framework includes three enabling technologies: (1) automatic parcellation of structural MRI GM into 76 precisely defined neuroanatomic subregions ("76-space"), (2) automated segmentation of GM, WM and CSF based on DTI data, and (3) automatic measurement of the average apparent diffusion coefficient (ADC) in each segmented GM subregion. We evaluate and validate this computational framework for 76-space GM diffusivity analysis using data from normal volunteers and from patients with Creutzfeldt-Jakob disease.

Adult↗
PubMedDate not supplied

Monitoring sarcomere structure changes in whole muscle using diffuse light reflectance.

Normal biomechanical and physiological functions of striated muscles are facilitated by the repeating sarcomere units. Light scattering technique has been used in studying single extracted muscle fibers. However, few studies, if any, have been conducted to investigate the possibility of using optical detection to examine sarcomere structure changes in whole muscles. We conducted a series of experiments to demonstrate that optical scattering properties measured in whole muscle are related to changes in sarcomere structure. These results suggest that photon migration technique has a potential for characterizing in vivo tissue ultrastructure changes in whole muscle.

Animals↗
PubMed2004

In vivo measurement of brain extracellular space diffusion by cortical surface photobleaching.

Molecular diffusion in the brain extracellular space (ECS) is an important determinant of neural function. We developed a brain surface photobleaching method to measure the diffusion of fluorescently labeled macromolecules in the ECS of the cerebral cortex. The ECS in mouse brain was labeled by exposure of the intact dura to fluorescein-dextrans (M(r) 4, 70, and 500 kDa). Fluorescein-dextran diffusion, detected by fluorescence recovery after laser-induced cortical photobleaching using confocal optics, was slowed approximately threefold in the brain ECS relative to solution. Cytotoxic brain edema (produced by water intoxication) or seizure activity (produced by convulsants) slowed diffusion by >10-fold and created dead-space microdomains in which free diffusion was prevented. The hindrance to diffusion was greater for the larger fluorescein-dextrans. Interestingly, slowed ECS diffusion preceded electroencephalographic seizure activity. In contrast to the slowed diffusion produced by brain edema and seizure activity, diffusion in the ECS was faster in mice lacking aquaporin-4 (AQP4), an astroglial water channel that facilitates fluid movement between cells and the ECS. Our results establish a minimally invasive method to quantify diffusion in the brain ECS in vivo, revealing stimulus-induced changes in molecular diffusion in the ECS with unprecedented spatial and temporal resolution. The in vivo mouse data provide evidence for: (1) dead-space ECS microdomains after brain swelling; (2) slowed molecular diffusion in the ECS as an early predictor of impending seizure activity; and (3) a novel role for AQP4 as a regulator of brain ECS.

Animals↗
PubMed2006

P1 plasmid partition: in vivo evidence for the ParA- and ParB-mediated formation of an anchored parS complex in the absence of a partner parS.

ParA and ParB proteins and cis-acting site, parS, are required to partition plasmid P1 faithfully to daughter cells. The process may initiate from plasmids paired by ParB at which recruited ParA then acts to effect the separation. We previously reported evidence for ParB-mediated pairing of parS sites on plasmids in the absence of ParA. In DNA gyrase-inhibited cells, the pairing prevented diffusion of transcription-generated positive supercoils. This supercoil trapping was almost entirely in plasmid dimers, where the location of the parS sites in cis facilitated their pairing. Here we show that the addition of ParA blocked supercoil diffusion also in plasmid monomers. The possibility that this result is attributed to an enhancement by ParA of ParB-mediated pairing in trans is consistent with our finding that ParA appeared to partially suppress the pairing defect of two mutant ParB proteins. However, enhanced pairing alone could not account for the diffusion barrier in plasmid monomers; it was manifest in monomers even when they were largely devoid of partners in the same cell. Apparently, ParA altered the ParB-parS complex such that it could no longer swivel, most likely by anchoring it, a reaction of probable relevance to partition.

Bacterial Proteins↗
PubMed2001

Acute stroke patterns in patients with internal carotid artery disease: a diffusion-weighted magnetic resonance imaging study.

BACKGROUND AND PURPOSE: Diffusion-weighted (DW) MRI is a sensitive method that facilitates early stroke pattern identification. There are limited data about the influence of stenosis grade on the development of particular stroke patterns in internal carotid artery (ICA) disease. We therefore investigated the lesion patterns on DW MRI in acute stroke patients with ICA disease. METHODS: DW MRI was analyzed in 102 consecutive acute stroke patients with different degrees of ipsilateral ICA disease. Patients were assigned to 1 of 5 observed lesion patterns: (1) territorial ischemia, (2) subcortical ischemia without or (3) with embolus fragmentation, (4) disseminated lesions in distal cortical regions, and (5) multiple lesions in hemodynamic risk zones. In addition, perfusion-weighted (PW) MRI and MR angiography information was included in the assessment. RESULTS: All patterns were observed in the different stages of ICA disease. Half of the patients with high-grade or subtotal stenosis had lesions in hemodynamic risk zones. Territorial stroke occurred in 47.6% of patients with ICA occlusion. Statistical analysis showed a significant relationship between the degree of stenosis and the observed stroke pattern (P=0.001). In 77.8% of patients exhibiting high-grade ICA stenosis, subtotal stenosis, or occlusion, the perfusion lesion was larger than the diffusion lesion (PW/DW mismatch). CONCLUSIONS: Although in the individual patient any of the infarct patterns may occur, in statistical terms the incidence of a particular stroke pattern is clearly dependent on the degree of stenosis.

Aged↗
PubMed1988

Measurement of myoglobin diffusivity in the myoplasm of frog skeletal muscle fibres.

1. Experiments were carried out on intact, single skeletal muscle fibres from frog in order to estimate the apparent diffusion constant of myoglobin (denoted DAPP) in the myoplasm of living muscle cells. An optical technique was employed to measure myoglobin concentration along the fibre axis following injection of metmyoglobin (denoted metMb) at a point source. The concentration profiles were fitted by the one-dimensional diffusion equation to give estimates of DAPP. The method relied on the fact that myoglobin is normally absent from these frog fibres, thus permitting resolution of the myoglobin-related absorbance above the intrinsic absorbance of the fibre. 2. One complication in the method was that metMb became significantly reduced to oxymyoglobin (denoted MbO2) during the elapsed time before measurement of the concentration profile. The rate of reduction was evaluated by fitting myoglobin-related absorbance spectra, measured at different times following injection of metMb, with in vitro absorbance spectra of metMb and MbO2. Results from four experiments indicated that reduction could be described by a first-order, irreversible reaction having an average rate constant of 0.0164 min-1 (22 degrees C). The effect of reduction on the fitting of DAPP was taken into account. 3. DAPP was determined under three fibre conditions: (1) long sarcomere spacing (3.6-3.8 microns) at 16 degrees C, (2) long sarcomere spacing at 22 degrees C, and (3) normal sarcomere spacing (2.4-2.7 microns) at 22 degrees C. The average values for DAPP under these conditions were: (1) 0.12 (n = 5); (2) 0.17 (n = 5); and (3) 0.15 (n = 7) x 10(-6) cm2 s-1. The average value at 22 degrees C, 0.16 x 10(-6) cm2 s-1, is about 4 times smaller than values for myoglobin diffusivity at 20 degrees C commonly assumed in models of facilitated transport of oxygen by myoglobin. 4. In order to test the possibility that the unexpectedly low value of DAPP found in intact fibres might be due to the binding of myoglobin to relatively immobile sites in myoplasm, experiments were carried out in a cut-fibre preparation using a technique described by Maylie, Irving, Sizto & Chandler (1987 b) for determining the diffusion constants and degree of myoplasmic binding of absorbance dyes. Values for DAPP and the factor (denoted 1 + beta) by which the total myoglobin concentration exceeded the free myoglobin concentration were obtained by fitting the absorbance data by solutions of the one-dimensional diffusion equation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2003

Social behaviors as determined by different arrangements of social consequences: diffusion of responsibility effects with competition.

According to a recently proposed synthesis, social loafing, social facilitation, and deindividuation can be viewed as different ways of arranging social consequences (B. Guerin, 1999). The effects of such arrangements have been measured in past research as productive output (social loafing and social facilitation) or as antinormative behaviors (deindividuation), but all 3 effects are manipulable by changing individual identifiability, evaluation, social identity, task difficulty, and presence in a group. The synthesis also predicted that these same variables would apply to other measures and other arrangements of social consequences. To this end, in the present 2 experiments, the author varied the arrangements for consequence diffusion in a competition situation by varying small and large competing groups and measured productive output and antinormative behaviors simultaneously. The 2 experiments showed social-consequence effects in competition situations with college students, giving further support for the social-consequence synthesis and the idea that the verbal naming of phenomena in social psychology is arbitrary.

Competitive Behavior↗
PubMed1981

Diffusion-driven mechanisms of protein translocation on nucleic acids. 1. Models and theory.

Genome regulatory proteins (e.g., repressors or polymerases) that function by binding to specific chromosomal target base pair sequences (e.g., operators or promoters) can appear to arrive at their targets at faster than diffusion-controlled rates. These proteins also exhibit appreciable affinity for nonspecific DNA, and thus this apparently facilitated binding rate must be interpreted in terms of a two-step binding mechanism. The first step involves free diffusion to any nonspecific binding site on the DNA, and the second step comprises a series of protein translocation events that are also driven by thermal fluctuations. Because of nonspecific binding, the search process in the second step is of reduced dimensionality (or volume); this results in an accelerated apparent rate of target location. In this paper we define four types of processes that may be involved in these protein translocation events between DNA sites. These are (i) "macroscopic" dissociation--reassociation processes within the domain of the DNA molecule, (ii) "microscopic" dissociation--reassociation events between closely spaced sites in the DNA molecule, (iii) "intersegment transfer" (via "ring-closure") processes between different segments of the DNA molecule, and (iv) "sliding" along the DNA molecule. We present mathematical and physical descriptions of each of these processes, and the consequences of each for the overall rate of target location are worked out as a function of both the nonspecific binding affinity between protein and DNA and the length of the DNA molecule containing the target sequence. The theory is developed in terms of the Escherichia coli lac repressor--operator interaction since data for testing these approaches are available for this system [Barkley, M. (1981) Biochemistry 20, 3833; Winter, R. B., & von Hippel, P. H. (1981) Biochemistry (second paper of three in this issue); Winter, R. B., Berg, O. G., & von Hippel, P. H. (1981) Biochemistry (third paper of three in this issue)]. However, we emphasize that this approach is general for the analysis of mechanisms of biological target location involving facilitated transfer processes via nonspecific binding to the general system of which the target forms a small part.

Binding Sites↗
PubMed1985

Gap junctions and direct intercellular communication between rat uterine smooth muscle cells.

We have tested the hypothesis that an increase in direct intercellular communication accompanies the development of gap junctions (GJs) between rat uterine smooth muscle cells at parturition. Intercellular communication in these tissues was studied by exposing one portion of small strips of myometrium to 2-[3H]deoxy-D-glucose (2-DG) and determining the longitudinal distribution of tracer after a 5-h period of diffusion. The distribution of 2-DG was greater in parturient compared with ante- and postpartum tissues. Similarly, the apparent diffusion coefficient of 2-DG was almost 10-fold greater in delivering tissues (1.86 X 10(-6) cm2/s) than before (0.199 X 10(-6) cm2/s) or after (0.296 X 10(-6) cm2/s) parturition. Control experiments indicated that the redistribution of 2-DG was dependent on the presence of GJs and was the result of intracellular and direct cell-to-cell diffusion. The appearance of GJs is the myometrium at term facilitates direct intercellular communication between uterine smooth muscle cells during labor. This improved communication may be responsible for synchronizing and coordinating electrical, metabolic, and contractile activity in the uterine wall and, hence, the effective expulsion of fetuses.

Animals↗
PubMed1984

Dynamics of intracellular calcium and its possible relationship to phasic transmitter release and facilitation at the frog neuromuscular junction.

We have developed a mechanistic model for intracellular influx, diffusion, and efflux of calcium, and we compare its predictions to the dynamics of transmitter release at the frog's motor nerve terminal. The model includes a square wave influx of calcium, a linear or saturable pump for the efflux of calcium, and slow diffusion of calcium within the terminal due to rapid equilibrium binding of the major portion of the influx to fixed, nonsaturable sites in the cytoplasm. Transmitter release is taken as proportional to the fourth power of the calcium concentration in a region within 100 A of the surface membrane. The model predicts phasic release of transmitter with a time course similar to that of the endplate current--it turns on with a lag, rises rapidly to a peak, and then declines more slowly. It also predicts facilitation, the increased transmitter release in response to a second stimulus for many milliseconds after the initial transmitter release has ceased. This facilitation is similar to that reported at the frog neuromuscular junction in its initial amplitude and time course.

Animals↗
PubMed1966

Diffusivity measurements of human methemoglobin.

Experimental measurements of the diffusion coefficient of human methemoglobin were made at 25 degrees C with a modified Stokes diaphragm diffusion cell. A Millipore filter was used in place of the ordinary fritted disc to facilitate rapid achievement of steady state in the diaphragm. Methemoglobin concentrations varied from approximately 5 g/100 ml to 30 g/100 ml. The diffusion coefficient in this range decreased from 7.5 x 10(-7) cm(2)/sec to 1.6 x 10(-7) cm(2)/sec.

Chemical Phenomena↗
PubMed2000

Modelling the production of nitric oxide within the human airways.

The measurement of exhaled nitric oxide (NO) is well established for monitoring of airway inflammation in bronchial asthma. It is known that the concentration of NO determined as steady state (plateau) value at a constant expiratory flow rate depends on the flow rate chosen. This suggests that the exhaled NO is released within the conducting airways, whereas alveolar NO levels are negligible. The processes involved can be described through a lung model comprising an alveolar compartment and an airway compartment thought of as a pipe. This concept has been formulated mathematically and the models proposed in the literature are essentially equivalent. NO plateau levels obtained at different flow rates allow the estimation of 1) an effective airway wall NO concentration that represents the driving force for NO release, 2) an airway diffusing capacity for NO which depends on factors impeding or facilitating NO transport, including an increase in NO-producing surface area. Clinical studies will have to assess whether the knowledge of these or related parameters offers a significant advantage over the determination of exhaled NO at a single flow rate.

Biological Transport↗
PubMed1997

Organization of the projections from the pericruciate cortex to the pontomedullary brainstem of the cat: a study using the anterograde tracer Phaseolus vulgaris-leucoagglutinin.

The anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) was used to study the distribution and density of the projections that originate from four identified subdivisions of the pericruciate cortex (namely, the forelimb and hind limb representations of area 4, area 6a beta, and area 6a gamma) and that terminate in the pontomedullary brainstem in the cat. Injections of PHA-L in all areas of the pericruciate cortex labelled numerous fibers and their terminal swellings in the brainstem. The major target regions of all four cortical areas were the pontine nuclei and the pontomedullary reticular formation (PMRF). Injections into both the forelimb and hind limb representations of area 4 and into area 6a beta resulted in a dense pattern of terminal labelling in restricted regions of the medial and lateral parts of the ipsilateral pontine nuclei. The labelling following the area 6a beta injection was spatially distinct from that seen following the area 4 injections. Injections into the forelimb representation of area 4 as well as into area 6a beta and 6a gamma resulted in the labelling of numerous terminal swellings bilaterally in the PMRF; in contrast, there were few labelled terminal swellings in the PMRF following injections into the hind limb representation of area 4. Terminal swellings on individual corticoreticular fibers were far less densely aggregated than those in the pontine nuclei. The dense pattern of innervation to restricted regions of the pontine nuclei supports previous suggestions that the corticopontine projections retain a high degree of topographical specificity that could be used in the control of discrete voluntary movements. In contrast, the more diffuse pattern of the projections to the PMRF may facilitate the selection and activation of the complex postural patterns that accompany voluntary movement.

Animals↗
PubMed1995

A method for characterizing transition concertedness from polymer dynamics computer simulations.

A statistical method based on classifying the transitions among a set of dihedral angles within an "energy transfer window" is developed, and used to analyze Brownian (BD) and molecular dynamics (MD) simulations of the acyl chains in a lipid bilayer, and MD of neat hexadecane. It is shown for the BD simulation that when a transition of the dihedral angle in the center of the chain occurs, a transition of a particular next nearest neighbor (or angle 2-apart) will follow concertedly with a probability of approximately 0.10 within a time window of approximately 3 ps. The MD bilayer simulations, which are based on a more flexible model of the hydrocarbon chains, yield corresponding concerted transition probabilities of approximately 0.083 and window sizes of 1-2 ps. An analysis of angles 4-apart yields concerted transition probabilities of 0.03 and 0.04 for the BD and MD bilayer simulations, respectively, and window sizes close to those of the corresponding 2-apart cases. Statistical hypothesis testing very strongly rejects the assertion that these follower transitions are occurring at random. Similar analysis reveals marginal or no evidence of concertedness between 1-apart (nearest neighbor) and between 3-apart dihedral angle transitions. The pattern of concertedness for hexadecane is qualitatively similar to that of the lipid chains, although concertedness is somewhat stronger for the 3-apart transitions and somewhat weaker for those 4-apart. Finally, it is suggested that the diffusion of small solute molecules in membranes is better facilitated by nonconcerted transitions, which are associated with relatively large displacements of the chains, than by concerted transitions, which do little to change the chain shape.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1992

Correlation between epidermal growth factor receptor concentration and the growth of human gastric cancer xenografts in nude mice.

Seven human gastric cancer xenografts with different concentrations of EGF receptor were established in nude mice. The expression of EGF receptor in the tumors was demonstrated by Western blotting with anti-EGF receptor antibody, binding assay with 125I-EGF and immunohistochemistry with anti-EGF receptor antibody. Western blotting revealed EGF receptor doublet bands at molecular masses of 150 KDa and 170 KDa in all of the samples. The concentration of 125I-EGF binding activity in the tumors ranged from 36.0 to 11,000 fmol/mg protein, with a mean of 345 fmol/mg protein. EGF receptor was also demonstrated immunohistochemically on the apical border of the glands and the cell membrane of the tumor cells. There seemed to be a close correlation between the concentration of 125I-EGF binding activity and the doubling time of these tumors in nude mice (gamma = -0.68). However, no definite correlation was observed between EGF ligand binding and histological features of intestinal type or diffuse type. The expression of EGF receptor appears to facilitate the growth of human gastric cancer xenografts in nude mice.

Animals↗
PubMed1996

Preparation of bank bone using defatting, freeze-drying and sterilisation with ethylene oxide gas. Part 2. Clinical evaluation of its efficacy and safety.

We used bone allograft treated by defatting in chloroform and methanol, freeze-drying and sterilisation with ethylene oxide gas in operations on 396 patients. The purpose of defatting and freeze-drying is to facilitate subsequent sterilisation by eliminating a barrier to the diffusion of ethylene oxide gas into bone, to lower the residual levels of the ethylene oxide and its toxic by-products after sterilisation, to eliminate alloantigens and to make storage at room temperature possible. Postoperative infections confirmed by a positive bacterial culture occurred in 2 of the 396 patients receiving the allograft, which was prepared under clean, but not sterile, conditions, one of which was thought to be due to dehiscence of the wound, rather than to the allograft. There were also 3 probable infections. Histological sections of the area around the interface of the allograft and its bony bed showed: (1) osteoblasts lining the surface of the dead cortical bone of the graft with appositional new bone; (2) ingrowth of new bone into the Haversian canals, and (3) little infiltration of inflammatory small round cells. These findings indicated the ability of the bone to support new bone formation and to eliminate antigens. The low incidence of infection confirmed the efficacy of this method of sterilisation.

Adolescent↗