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PubMed2007

Novel role of AQP-1 in NO-dependent vasorelaxation.

Nitric oxide (NO) produced by endothelial cells diffuses to vascular smooth muscle cells to cause dilatation of the renal vasculature and other vessels. Although it is generally assumed that NO moves from cell to cell by free diffusion, we recently showed that aquaporin-1 (AQP-1) transports NO across cell membranes. AQP-1 is expressed in endothelial and vascular smooth muscle cells. We hypothesized that diffusion of NO into vascular smooth muscle cells and out of endothelial cells is facilitated by AQP-1, and transport of NO by AQP-1 is involved in endothelium-dependent relaxation. In intact aortic rings from AQP-1 -/- mice, vasorelaxation induced by acetylcholine (which increases endogenous NO) was reduced (P < 0.0001 vs. control). No differences were found in the relaxation caused by intracellular delivery of NO or intracellular cGMP between strains. In endothelium-denuded aortic rings from AQP-1 -/- mice, the vasorelaxant capability of NO released in the extracellular space was reduced (P < 0.0001 vs. control). Influx of NO (5 microM) into vascular smooth muscle cells was 0.17 +/- 0.02 f.u./s for control and 0.07 +/- 0.01 f.u./s for AQP-1 -/- mice, 62% lower (P < 0.002). NO released by endothelial cells in response to 1 microM acetylcholine was 96.2 +/- 17.7 pmol NO/mg for control and 41.9 +/- 13.4 pmol NO/mg for AQP-1 -/- mice, 56% reduction (P < 0.04). NOS3 expression was 1.33 +/- 0.29 O.D. units for control and 3.84 +/- 0.76 O.D. units for AQP-1 -/- mice, 188% increase (P < 0.01). We conclude that 1) AQP-1 facilitates NO influx into vascular smooth muscle cells, 2) AQP-1 facilitates NO diffusion out of endothelial cells, and 3) transport of NO by AQP-1 is required for full expression of endothelium-dependent relaxation.

Acetylcholine↗
PubMed2003

Self-diffusion coefficient by single-sided NMR.

It is presented a novel method for the measure of the self-diffusion coefficient. The method exploits the fixed gradient of an open magnet, as that used in single-sided NMR, and it does not use prior information on T(2). The approach presented in this paper can be practiced also on the fringe field of superconducting magnets and it is based on the construction of the ratios between echoes taken at different interpulses separation in a Carr-Purcell-Meiboom-Gill pulse sequence. The determination of the self-diffusion coefficient facilitates the estimate of T(2) because the transverse relaxation results almost influenced by the molecular diffusion effect, also at the shorter interpulses time, when it is measured in field strongly inhomogeneous.

Journal Article↗
PubMed1991

Characteristics of activity-dependent potassium accumulation in mammalian peripheral nerve in vitro.

Ion-sensitive microelectrodes were used to study the behavior of extracellular ions in rat sciatic nerve during and following activity. Nerve stimulation produced increases in [K+]o that were dependent upon the frequency and duration of stimulation; no change in extracellular pH occurred with stimulation. Increases in [K+]o depended on axonal discharge since they were blocked by inhibiting sodium channels with tetrodotoxin. At 22 degrees C, stimulation could induce increases in [K+]o of several mM; at 36 degrees C, stimulation rarely produced increases in [K+]o greater than 1 mM. Stimulated increases in [K+]o dissipated very slowly (i.e. t 1/2 = 50-100 s) and the rate of dissipation was not significantly affected by anoxia, changes in temperature, changes in extracellular pH, or the application of a blocker of Na+, K(+)-ATPase (ouabain) or a K+ channel blocker (Ba2+). In comparison to the central nervous system, neural activity in rat sciatic nerve produced smaller increases in [K+]o and these increases dissipated much more slowly. The primary mechanism of K+ dissipation appeared to be diffusion, probably facilitated by the larger extracellular space in peripheral nerve compared to the central nervous system, but impeded by diffusion barriers imposed by the blood-nerve barrier.

Action Potentials↗
PubMed1993

Transport across the bacterial outer membrane.

Diffusion of small molecules across the outer membrane of gram-negative bacteria may occur through protein channels and through lipid bilayer domains. Among protein channels, many examples of trimeric porins, which produce water-filled diffusion channels, are known. Although the channels are nonspecific, the diffusion rates of solutes are often drastically affected by their gross physicochemical properties, such as size, charge, or lipophilicity, because the channel has a dimension not too different from that of the diffusing solutes. In the last few years, the structures of three such porins have been solved by X-ray crystallography. It is now known that a monomer unit traverses the membrane 16 times as beta-strands, and one of the external loop folds back into the channel to produce a narrow constriction. Most of the static properties of the channel, such as the pore size and the position of the amino acids that produce the constriction, can now be explained by the three-dimensional structure. Controversy, however, still surrounds the issue of whether there are dynamic modulation of the channel properties in response to pH, ionic strength, or membrane potential, and of whether such responses are physiological. More recently, two examples of monomeric porins have been identified. These porins allow a very slow diffusion of solutes, but the reason for this low permeability is still unclear. Finally, channels with specific binding sites facilitate the diffusion of specific classes of nutrients, often those compounds that are too large to penetrate rapidly through the porin channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Outer Membrane Proteins↗
PubMed1999

[Influence of decocting time on the amount of anthraguinone diffused from Cassia seeds].

OBJECTIVE: To study the influence of decocting time on the amount of anthraquinone diffused from the cassia seeds. METHOD: The amount of anthraquinone in the decoctions made in different lengths of decocting time was determined by spectrophotometry (for intact seeds and powdered seeds). RESULT: Fast nonlinear diffusion district, slow linear diffusion district and ceasing diffusion district were shown on the light absorption-decocting time curves, and appropriate smashing of the cassia seed facilitated the diffusion of anthraquinone. CONCLUSION: The best decocting time for anthraquinone to diffuse from the cassia seeds should be the ending time of the fast nonlinear diffusion district, while the second decoction should not be given up.

Anthraquinones↗
PubMed1984

Evidence for rotational contribution to protein-facilitated proton transport.

Two modes of molecular motion of carrier molecules can, in principle, lead to a facilitated transport of a substrate: translational and rotational diffusion. In the present study, which deals with the mechanism of the facilitated diffusion of H+ and O2 in solutions of earthworm hemoglobin, examples for both types of facilitation are presented. Only translational, not rotational, diffusion of earthworm hemoglobin appears to lead to a facilitated O2 flux. In contrast, substantial facilitated H+ fluxes of comparable size arise from rotational diffusion as well as from translational diffusion of this large protein. This is derived from measurements of facilitated H+ and O2 fluxes in earthworm hemoglobin solutions and determinations of the rotational and translational diffusion coefficients of earthworm hemoglobin with the help of a theoretical treatment of facilitated diffusion by rotational carrier diffusion. H+ transport by rotational protein diffusion appears to be a case where the often-postulated mechanism of facilitated transport by rotation of a carrier lends itself to experimental verification.

Biological Transport↗
PubMed1993

Effect of smear layer removal on the diffusion of calcium hydroxide through radicular dentin.

Forty single-rooted teeth were sectioned transversely through the cementoenamel junction and instrumented to a size #50 K-Flex file at the working length by saline irrigation. Each root was placed in a dilution vial containing 10 ml of normal saline, and the pH and Ca2+ levels were recorded after 24 h. The roots in group 1 then received a final irrigation with 20 ml of normal saline. Group 2 received a final irrigation with 10 ml of 17% ethylenediaminetetraacetic acid followed by 10 ml of 5.25% NaOCl to remove the smear layer. Group 3 was irrigated in the same manner as group 2, but calcium hydroxide (CH) was placed into the root canal. Group 4 was irrigated with 20 ml of NaOCl, and CH was placed into the root canal. The pH and Ca2+ levels were recorded at 1, 3, 5, and 7 days. After 7 days a 3- x 3- x 1-mm external defect was created in the coronal one third of the root surface. The pH and Ca2+ levels were subsequently recorded at 1, 3, and 7 days. Groups 3 and 4 demonstrated significantly higher H+ and Ca2+ levels than did groups 1 and 2 three days after CH placement and at all subsequent intervals. Group 3 demonstrated significantly higher H+ and Ca2+ readings at some but not all intervals. The results demonstrated that CH diffuses from the root canal to the exterior surface of the root and that the removal of the smear layer may facilitate this diffusion.

Analysis of Variance↗
PubMed1999

Effect of temperature and calcium on transneuronal diffusion of DiI in fixed brain preparations.

The lipophilic tracer 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) was used to label neuronal pathways in fixed goldfish brains. The normal procedure involving 4% paraformaldehyde as a fixative, applying DiI and storing the brain in the fixative at 40 degrees C resulted in many cases in a rather diffuse labeling of fiber pathways and the occurrence of transneuronally labeled cells and fibers. We found that calcium and heat both facilitate the diffusion of DiI out of membranes in vibratome sections. We modified the protocol by adding the calcium binding substance ethylenediamine tetraacetate to all solutions and incubated at room temperature. This improved the sharpness of labeled structures and eliminated the transneuronal labeling in our material. Although transneuronal transport of the tracer may still occur under certain circumstances, the present modification of the DiI staining procedure substantially increased the staining quality and reproducibility and decreased the occurrence of transneuronal labeling.

Animals↗
PubMed1998

Thinning of the intervascular tissue layers of the human placenta is an adaptive response to passive diffusion in vivo and may help to predict the origins of fetal hypoxia.

OBJECTIVES: To test the hypothesis that thinning of the placental intervascular layers, and greater variability in thickness, are positive adaptations to facilitate passive diffusion and may help to resolve different categories of fetal hypoxia. STUDY DESIGN: Placentas from 12-41 weeks of normal gestation and from pregnancies associated with fetal hypoxic stress (high altitude, diabetes mellitus) were sampled systematically, fixed in formalin, wax-embedded and quantified using stereological methods. Arithmetic and harmonic mean distances across villous trophoblast, stroma and fetal plasma were estimated by measuring randomly sampled intercept lengths. In each case, an index of variability of layer thickness was calculated by dividing the arithmetic by harmonic mean distance. This index has the value I when a tissue layer is uniformly thick but increases in value as local layer thickness becomes more variable. Comparisons between groups were drawn using variance and regression analysis. RESULTS: During pregnancy, there were significant negative correlations between layer thickness (trophoblast, stroma) and gestational age and fetal weight, and significant positive correlations between thickness irregularity and age and weight. Compared with lowland controls, high-altitude placentas possessed thinner layers but only the trophoblast and stroma (and not fetal plasma) were more variably thick. In maternal diabetes, only fetal plasma distance was reduced but fetal and stromal layers appeared to be more irregular in thickness. CONCLUSIONS: Alterations in placental intervascular layer thicknesses occur in normal and abnormal pregnancies and represent real adaptations leading to improved diffusive conductances. Differences in the tissue location of the adaptive response may depend on the nature and origins of the fetal hypoxia.

Adaptation, Physiological↗
PubMed1977

Diffusion of carbon dioxide through lipid bilayer membranes: effects of carbonic anhydrase, bicarbonate, and unstirred layers.

Diffusion of (14)C-labeled CO(2) was measured through lipid bilayer membranes composed of egg lecithin and cholesterol (1:1 mol ratio) dissolved in n-decane. The results indicate that CO(2), but not HCO(3-), crosses the membrane and that different steps in the transport process are rate limiting under different conditions. In one series of experiments we studied one-way fluxes between identical solutions at constant pCO(2) but differing [HCO(3-)] and pH. In the absence of carbonic anhydrase (CA) the diffusion of CO(2) through the aqueous unstirred layers is rate limiting because the uncatalyzed hydration-dehydration of CO(2) is too slow to permit the high [HCO(3-)] to facilitate tracer diffusion through the unstirred layers. Addition of CA (ca. 1 mg/ml) to both bathing solutions causes a 10-100-fold stimulation of the CO(2) flux, which is proportional to [HCO(3-)] over the pH range 7-8. In the presence of CA the hydration- dehydration reaction is so fast that CO(2) transport across the entire system is rate limited by diffusion of HCO(3-) through unstirred layers. However, in the presence of CA when the ratio [HCO(3-) + CO(3=)]:[CO(2)] more than 1,000 (pH 9-10) the CO(2) flux reaches a maximum value. Under these conditions the diffusion of CO(2) through the membrane becomes rate limiting, which allows us to estimate a permeability coefficient of the membrane to CO(2) of 0.35 cm s(-1). In a second series of experiments we studied the effects of CA and buffer concentration on the net flux of CO(2). CA stimulates the net CO(2) flux in well buffered, but no in unbuffered, solutions. The buffer provides a proton source on the upstream side of the membrane and proton sink on the downstream side, thus allowing HCO(3-) to facilitate the net transport of CO(2) through the unstirred layers.

Bicarbonates↗
PubMed1990

A versatile model of steady state O2 supply to tissue. Application to skeletal muscle.

A model of combined convective and diffusive O2 transport to tissue is suggested which allows for the calculation of PO2 distributions in a cuboid tissue region with arbitrary microvascular geometries and blood flows. Carrier-facilitated O2 diffusion in the erythrocytes and in the tissue and red blood cell reaction kinetics are considered. The model is based on analytical descriptions of the PO2 fields of single erythrocytes surrounded by carrier-free layers in an infinite three-dimensional space containing an O2 carrier such as myoglobin. These PO2 fields are overlaid to obtain a solution of the differential equation of diffusion in respiring tissue. The model has been applied to a situation in heavily working skeletal muscle. Resulting PO2 profiles exhibit steep peri-capillary PO2 gradients. Further into the fiber, the profiles are essentially flat at low PO2 levels in good agreement with experimental findings (Gayeski and Honig. 1986. Am. J. Physiol. 251:H789-H799). PO2 dependence of facilitation of O2 transport produces a "layer deficient of functional carrier" which extends into the muscle fiber and which represents a reserve of O2 conductance automatically recruited in exercise. Furthermore, it results in a homogenization of red blood cell O2 fluxes which accounts for the absence of PO2 gradients along the muscle fiber axis (cf. Gayeski and Honig. 1988. Am. J. Physiol. 254: H1179-H1186).

Animals↗
PubMed2006

Investigation of interparticle interactions of larger (4.63 nm) monolayer protected gold clusters during quantized double layer charging.

In this article, the effect of interparticle interactions of 4.63 nm sized monolayer protected gold clusters (Au MPCs) during quantized double layer (QDL) charging has been investigated using electrochemical techniques. Voltammetry and scanning tunneling microscopy have been used to compare their electron transfer behavior. Furthermore, since the QDL process is diffusion controlled, the diffusion coefficient values have been estimated at various charge steps using two independent electroanalytical techniques, viz. chronoamperometry and impedance. These results show that higher core charge facilitates higher diffusion coefficient values, and indicate that repulsive interactions dominate for charged MPCs compared to those of its neutral analogue, which are mainly attractive in nature. Additionally, the electron transfer rate constants at various charge steps have been estimated from the impedance results, showing comparatively faster electron transfer rate at higher charge states.

Algorithms↗
PubMed2005

Barriers and pathways to diffusion of methamphetamine use among African Americans in the rural South: preliminary ethnographic findings.

There are no studies of African Americans methamphetamine use in the South where it is widespread among whites. We describe factors that inhibit or facilitate the diffusion of methamphetamine use among African Americans based on qualitative interviews with 86 drug users in rural Arkansas and Kentucky. Results suggest low prevalence of methamphetamine use among African Americans, and interviewees cited several barriers to its diffusion which were linked to the drug's ingredients, psychoactive and physiological effects, difficulty in accessing distribution networks, and established African-American preference for cocaine. Fourteen African Americans reported methamphetamine use and discussed pathways to it. Possible increases in African- American methamphetamine use merits further investigation.

Adult↗
PubMed2003

Ca2+ diffusion through dentin of Ca(OH)2 associated with seven different vehicles.

This investigation measured the diffusion of Ca2+ through dentin by using Ca(OH)2 associated with various vehicles. After mechanical preparation and removal of smear layer, 41 human premolar teeth were stored individually in flasks containing 800 ml of ultra-pure deionized water for 2855 h. The Ca2+ concentration was measured by atomic absorption spectrophotometry as a function of time. These measurements were divided into two phases: dissolution, to check the loss of Ca2+ from the tooth structure itself, for which all canals were kept empty and open in the absence of medication for 1168 h, and diffusion, in which the specimens were divided into 10 groups (3 control groups: group 1 = water control, group 2 = sealing control, and group 3 = open canal dissolution control; 7 experimental groups in which the whose canals were filled with Ca(OH)2 paste associated with the following vehicles: group 4 = saline; group 5 = polyethylene glycol (Calen); group 6 = glycerin and camphorated parachlorophenol group 7 = camphorated paramonochlorophenol; group 8 = glycerin; group 9 = glycerin and tricresol formaldehyde (TCF); and group 10 = anesthetic solution. This phase lasted 1687 h. A total of 1058 measurements of Ca2+ were made. Regression analysis was used for statistical evaluation. We concluded that diffusion occurred differently for each group: the medications used in the root canals interacted with the dentinal structure or among themselves; the medication coated the dentinal tubule, facilitating the diffusion of Ca2+ into the external part of the root.

Anesthetics, Local↗
PubMed2004

Modulation of rhythmic patterns and cumulative depolarization by group I metabotropic glutamate receptors in the neonatal rat spinal cord in vitro.

The role of group I metabotropic glutamate receptors (mGluRs), and their subtypes 1 or 5, in rhythmic patterns generated by the neonatal rat spinal cord was investigated. Fictive locomotor patterns induced by N-methyl-d-aspartate + serotonin were slowed down by the subtype 1 antagonists (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) or 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester (CPCCOEt) and unaffected by the subtype 5 antagonist 2-methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP). The group I agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) depolarized ventral roots and disrupted fictive locomotion, an effect blocked by AIDA (or CPCCOEt) and reversed by increasing the N-methyl-d-aspartate concentration. Cumulative depolarization induced by low frequency trains of dorsal root stimuli was attenuated by DHPG and unchanged by AIDA or MPEP while rhythmic patterns or motoneuron spike wind-up persisted. Disinhibited bursting induced by strychnine + bicuculline was accelerated by DHPG, slowed down by AIDA (which prevented the action of DHPG), unaffected by MPEP and counteracted by the selective group II agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine. The DHPG transformed regular bursting into arrhythmic bursting, a phenomenon also produced by the group II mGluR antagonist (2S)-alpha-ethylglutamic acid. These results indicate that, during fictive locomotion or disinhibited bursting, endogenous glutamate could activate discrete clusters of subtype 1 mGluRs to facilitate discharges. Diffuse activation by the exogenous agonist DHPG of group I mGluRs throughout spinal networks had an excitatory effect overshadowed by its much stronger depressant action due to concomitant facilitation of glycinergic transmission. Irregular disinhibited bursting caused by activation of subtype 1 receptors or block of group II receptors suggests that mGluRs could control not only the frequency but also the periodicity of bursting patterns, outlining novel mechanisms contributing to burst duration.

Action Potentials↗
PubMed2002

Actin dependence of polarized receptor recycling in Madin-Darby canine kidney cell endosomes.

Mammalian epithelial cell plasma membrane domains are separated by junctional complexes supported by actin. The extent to which actin acts elsewhere to maintain cell polarity remains poorly understood. Using latrunculin B (Lat B) to depolymerize actin filaments, several basolateral plasma membrane proteins were found to lose their polarized distribution. This loss of polarity did not reflect lateral diffusion through junctional complexes because a low-density lipoprotein receptor mutant lacking a functional endocytosis signal remained basolateral after Lat B treatment. Furthermore, Lat B treatment did not facilitate membrane diffusion across the tight junction as observed with ethylenediaminetetraacetic acid or dimethyl sulfoxide treatment. Detailed analysis of transferrin recycling confirmed Lat B depolarized recycling of transferrin from endosomes to the basolateral surface. Kinetic analysis suggested sorting was compromised at both basolateral early endosomes and perinuclear recycling endosomes. Despite loss of function, these two endosome populations remained distinct from each other and from early endosomes labeled by apically internalized ligand. Furthermore, apical and basolateral early endosomes were functionally distinct populations that directed traffic to a single common recycling endosomal compartment even after Lat B treatment. Thus, filamentous actin may help to guide receptor traffic from endosomes to the basolateral plasma membrane.

Actin Cytoskeleton↗
PubMed2006

Diffusion and economic consequences of health technologies in prostate cancer care in Sweden, 1991-2002.

OBJECTIVE: To describe the diffusion of six main health technologies used for management of prostate cancer, to estimate the economic consequences of technological changes, and to explore factors behind the diffusion. METHODS: Data describing the diffusion 1991-2002 were obtained from population-based databases. Costs were obtained from Linköping University Hospital and Apoteket AB. Factors affecting the diffusion of the technologies were explored. RESULTS: Utilization of technologies with a curative and/or palliative aim has increased over time, except for surgical castration. PSA-tests are used increasingly. The total cost of the study technologies has increased from 20 million euros in 1991 to 65 million euros in 2002. Classification of radical prostatectomy revealed a profile associated with a slow/limited diffusion, while classification of PSA-tests revealed a profile associated with a rapid/extensive diffusion. CONCLUSIONS: Several technological changes in the management of prostate cancer have occurred without proven benefits and have contributed to increased costs. There are other factors, besides scientific evidence, that have an impact on the diffusion. Consequently, activities aimed at facilitating an appropriate diffusion of new technologies are needed. The analytical framework used here may be helpful in identifying technologies that are likely to experience inappropriate diffusion and therefore need particular attention.

Diffusion of Innovation↗
PubMed1983

[Microspectrophotometry in the study of physiological and pathological events in erythrocytes].

Microspectrophotometry turns out to be the ideal method for an accurate study of single cells, namely of red blood cells, from the biochemical and physiological standpoint. Hereafter several possible applications are reported: a. the kinetics of gas-exchange (O2 and CO) in human erythrocytes has been made possible by the photosensitivity of the Hb-CO complex. In this way, it has been possible to establish that both ligands recombine with intraerythrocyte hemoglobin following a zero-order kinetic process. This suggested that diffusion of a ligand across an unstirred layer of buffer (approximately 5.10 mu thick) all around the cell could be the rate-limiting step of this recombination. Moreover, an intracellular facilitated oxygen diffusion has been observed and possible physiological implications have been shortly mentioned; b. the kinetics of intracellular polymerization of sickle cell hemoglobin in single red blood cells has been measured by quickly (approximately 1 msec) flashing-off the CO employing a cw Argon ion laser. The polymerization of deoxyhemoglobin has been followed by detecting the increased light scattering of the laser beam itself. The distribution of delay times (td) in several patients has been found significantly correlated to the severity of the disease, supporting the hypothesis that the td is a determinant factor in the pathophysiology of the disease. Possible therapeutic applications of this method are briefly discussed; c. the intraerythrocyte distribution of different hemoglobins of trout (Salmo irideus) among several erythrocytes has been observed by means of different physiochemical properties of single components. These turned out to be homogeneously present in all red blood cells studied.

Animals↗