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PubMedDate not supplied

Lipid diffusion in the plasma membrane of mouse spermatozoa: changes during epididymal maturation, effects of pH, osmotic pressure, and knockout of the c-ros gene.

It is well known that the plasma membranes of mammalian spermatozoa undergo extensive remodeling during maturation in the epididymal duct. In this investigation, we have used fluorescence recovery after photobleaching (FRAP) techniques to: 1) measure rates of lipid diffusion in the plasma membrane of mouse spermatozoa at different stages of maturation; 2) examine the effects of varying external conditions found in the epididymal duct (pH, temperature, and osmotic pressure) on lipid diffusion in mature sperm; and 3) investigate the effects of the c-ros null mutation that causes tail angulation in cauda spermatozoa after ejaculation as a result of cell swelling due to altered membrane function. Our results show that lipid diffusion (as measured using reporter probes 5-(N-octadecanoyl)aminofluorescein [ODAF] and 2-(6-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoyl-1-hexadecanoyl-sn-glycero-3-phosphocholine [NBD-C6-PC]) is several times faster across the membrane on the sperm head than on the tail and that it increases significantly during passage from caput to cauda. Temperature variations between 20 degrees C and 37 degrees C have a substantial effect on diffusion coefficients, with the sperm head being more responsive than the tail. Changes in external pH (6.5-8.5) or osmotic pressure (202-389 mOsm/kg), however, have little relative effect on lipid diffusion on any region of the sperm. The rate of diffusion of 22-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-23,24-bisnor-5-cholen-3beta-ol (NBD-cholesterol) is 10-fold higher across the head plasma membrane than across the tail and does not change significantly during epididymal maturation. Similarly, lipid diffusion in hairpin-shaped cauda sperm from c-ros (-/-) males is not significantly different from (+/+) controls. These results suggest that temperature and compositional changes are 2 of the important factors that regulate the dynamics of lipid molecules in the mouse sperm plasma membrane.

4-Chloro-7-nitrobenzofurazan↗

PubMed2003

Diffusion tensor imaging in cases of adrenoleukodystrophy: preliminary experience as a marker for early demyelination?

BACKGROUND AND PURPOSE: Diffusion tensor imaging measures the proton diffusivity and preferential orientation of the diffusion tensor. X-linked adrenoleukodystrophy is a demyelinating disease for which therapy depends on the onset and extension of demyelination. We investigated the ability of diffusion tensor imaging to detect changes in the demyelinated lesions and in the normal appearing white matter. METHODS: Diffusion tensor imaging of three related boys with X-linked adrenoleukodystrophy and seven age-matched control participants was performed. Isotropic diffusion (D') and fractional anisotropy (FA) values were determined in 18 regions of interest in the white matter of both hemispheres. RESULTS: In all the demyelinated white matter areas, a pattern with increased D' and loss of FA was found. For example, mean D' was 1.772 x 10(-3)mm(2)/s in patient 2 with blindness and extensive demyelination of the occipital white matter and was 0.693 x 10(-3)mm(2)/s in control participants (P =.01). In the same region, mean FA was 0.103 (0.464 in control participants, P <.0001). Significant alterations of D' and FA were also observed in normal appearing white matter. For example, mean D' was 0.802 x 10(-3)mm(2)/s in the parietal white matter of patient 1 with no visible alterations on T2-weighted images (0.715 x 10(-3) mm(2)/s in control patients, P =.03), whereas mean FA was 0.320 (0.400 in control participants, P =.003). CONCLUSION: Elevated D' and loss of FA revealed by diffusion tensor imaging are consistent with severe demyelination in patients with X-linked adrenoleukodystrophy. Significant alterations of D' and FA in normal appearing white matter may indicate early demyelination in areas that are not yet visibly altered on conventional MR images. Further evaluation in a larger series of patients and long-term study are needed.

Adolescent↗

PubMed2003

Dead-space microdomains hinder extracellular diffusion in rat neocortex during ischemia.

During ischemia, the transport of molecules in the extracellular space (ECS) is obstructed in comparison with healthy brain tissue, but the cause is unknown. Extracellular tortuosity (lambda), normally 1.6, increases to 1.9 in ischemic thick brain slices (1000 microm), but drops to 1.5 when 70,000 Mr dextran (dex70) is added to the tissue as a background macromolecule. We hypothesized that the ischemic increase in lambda arises from diffusion delays in newly formed dead-space microdomains of the ECS. Accordingly, lambda decreases when dead-space diffusion is eliminated by trapping dex70 in these microdomains. We tested our hypothesis by analyzing the diffusion of several molecules in neocortical slices. First we showed that diffusion of fluorescent dex70 in thick slices declined over time, indicating the entrapment of background macromolecules. Next, we measured diffusion of tetramethylammonium (TMA+) (74 Mr) to show that the reduction of lambda depended on the size of the background macromolecule. The synthetic polymer, 40,000 Mr polyvinylpyrrolidone, reduced lambda in thick slices, whereas 10,000 Mr dextran did not. The dex70 was also effective in normoxic slices (400 microm) after hypoosmotic stress altered the ECS to mimic ischemia. Finally, the dex70 effect was confirmed independently of TMA+ using fluorescent 3000 Mr dextran as a diffusion marker in thick slices: lambda decreased from 3.29 to 2.44. Taken together, these data support our hypothesis and offer a novel explanation for the origin of the large lambda observed in ischemic brain. A semiquantitative model of dead-space diffusion corroborates this new interpretation of lambda.

Animals↗

PubMed2003

Diffusion tensor imaging of the hippocampal formation in temporal lobe epilepsy.

BACKGROUND AND PURPOSE: Diffusion tensor imaging (DTI) is a noninvasive technique that can be used to assess the integrity of cerebral tissue. The purpose of this study was to assess DTI measurements in the hippocampal formation (HF) and to investigate the role of DTI in lateralizing the seizure focus in temporal lobe epilepsy (TLE). METHODS: We evaluated 12 patients with unilateral TLE and 14 healthy subjects. We collected diffusion-weighted images along six different directions with a b value of 1000 s/mm(2), as well as an image acquired without diffusion weighting (b = 0 s/mm(2)). A 1.5-T imager was used to acquire 17 (3-mm) coronal sections covering the temporal lobes. We compared the mean diffusivity (trace D) and fractional anisotropy (FA) from symmetrical voxels by sampling the anterior HF bilaterally. We compared measurements with the EEG, high-resolution MR imaging, and clinical information. RESULTS: The patient group had significantly increased diffusivity and decreased FA in the HF ipsilateral to the seizure focus, as compared with values in the contralateral HF. When compared with healthy subjects, patients had significantly higher mean diffusivity in the ipsilateral HF; ipsilateral FA values were lower and did not reach statistical significance. Measurements in the contralateral HF did not show differences. Left-right and absolute diffusivity indices lateralized the abnormal HF in eight and five of 12 patients, respectively. CONCLUSION: Abnormal DTI measurements and the epileptogenic HF are associated in unilateral TLE. This finding may reflect hippocampal sclerosis and may aid in presurgical evaluation.

Adult↗

PubMed2003

Diffusion correction of sodium sieving applicable in a peritoneal equilibration test.

Sodium sieving is a measure of free water transport. However its assessment is disturbed when a large difference exists between sodium concentrations in plasma and in dialysate--that is, when the diffusion rate is high. Based on previous findings concerning similarity in the mass transfer area coefficients (MTACs) of sodium and urate, we developed a model that corrects for high diffusion. The model enabled us to predict the dialysate sodium concentration resulting from diffusion alone at any time point during a dwell. The correction was based on knowledge of the intraperitoneal volume at any time point during the dwell, which can be calculated by using a volume marker (reference method). However, in a peritoneal equilibration test (PET), only the drained volume after 4 hours is available, and urate concentration is not routinely measured. Therefore, our objective in the present study was to investigate whether a diffusion correction using the MTAC of creatinine and the drained volume at the end of the dwell would be as accurate in estimating maximum sodium sieving as the reference method is. We analyzed standardized 4-hour dwells in 28 patients, 19 with stable PD and 9 with ultrafiltration failure. The dialysate consisted of a 3.86% glucose-containing solution to which dextran 70 was added as a volume marker. The correlation coefficient between the PET correction method and the reference method was 0.92 in all patients [0.90 in stable patients and 0.95 in the patients with ultrafiltration failure (p < 0.01 for all)]. We conclude that a diffusion correction for sodium can be made using PET data. A diffusion correction yields a better estimate of sodium sieving than does the sole use of the lowest dialysate-to-plasma (D/P) sodium irrespective of diffusion rate.

Adult↗

PubMed2004

[Preliminary study of astrocytic tumors by diffusion tensor imaging].

BACKGROUND & OBJECTIVE: Diffusion tensor imaging (DTI) is an advanced quantitative form of diffusion-weighted imaging. It could be used to calculate not only the apparent diffusion coefficient (ADC) of average water diffusion for each vowel, but also the diffusion anisotropic index of diffusion. Diffusion-weighted imaging is used in most of the studies of the brain tumors abroad. We used DTI method to measure the ADC, fractional anisotropy (FA) and relative anisotropy (RA), values of different tumor tissues and to evaluate the usefulness of ADC, FA, and RA in differentiating solid tumor, necrotic region, edema region, normal brain tissue, and in grading the malignancy of cerebral astrocytomas. METHODS: Fourteen cases of astrocytomas diagnosed (10 cases of grade 1-2 astrocytomas and 4 cases of grade 3-4 astrocytomas) were studied by DTI. ADC, FA, and RA values of different tumor tissue were measured. RESULTS: When all cases were analyzed as a group, significant differences of ADC were found in enhancing solid tumor (1.14+/-0.13x10(-3) mm(2)/s), necrotic region (2.04+/-0.50x10(-3) mm(2)/s), edema region (1.55+/-0.19x10(-3) mm(2)/s) compared with normal brain tissue (0.74+/-0.08x10(-3) mm(2)/s)(P< 0.05). Significant differences of ADC were also found in solid tumor (enhancing tissue:1.14+/-0.13x10(-3) mm(2)/s, non-enhancing tissue:1.01+/-0.25x10(-3) mm(2)/s) compared with necrotic region and edema region, respectively (P< 0.05). Significant differences of FA and RA were found in solid enhancing region (FA:0.21+/-0.08; RA:0.23+/-0.07), necrotic region (FA: 0.14+/-0.06, RA: 0.16+/-0.07), edema region (FA:0.16+/-0.04, RA:0.16+/-0.02) compared with normal brain tissue (FA: 0.37+/-0.06, RA: 0.38+/-0.07) (P< 0.05). No difference of FA and RA was found in solid tumor (including enhancing and non-enhancing tissue). Significant differences of ADC (P< 0.05), not FA and RA, were found between grade 1-2 astrocytomas (1.07+/-0.04x10(-3) mm(2)/s) and grade 3-4 astrocytomas (1.32+/-0.08x10(-3) mm(2)/s). CONCLUSION: Determination of ADC can be used to differentiate normal brain tissue from enhancing solid tumor, necrotic region, and edema region. Determination of FA and RA can be used to differentiate solid enhancing tumor, necrotic region, and edema region from normal brain tissue, but can not be used to differentiate solid tumor, necrotic region, and edema region. The ADC values, not FA and RA, may predict the degree of malignancy of astrocytic tumors.

Adult↗

PubMed2004

Water diffusion compartmentation at high b values in ischemic human brain.

BACKGROUND AND PURPOSE: We studied the evolution of brain water compartments during the early stage of ischemic stroke. METHODS: Diffusion-weighted imaging was performed at 1.5 T in 10 volunteers and 14 patients with stroke. We used a single-shot echo-planar technique with 11 b values of 0-5000 s/mm(2). Regions of interest were selected in the white matter (WM) and striatum of the volunteers and in the ischemic core of the patients. Measurements were fitted on the basis of a biexponential decay with the b factor as follows: S(b) = S(0)[(f(slow) x exp(-b x ADC(slow)) + (f(fast) x exp(-b x ADC(fast))] where S(b) is the signal intensity in the presence of a diffusion gradient, S(0) is the signal intensity without diffusion sensitization, ADC(slow) and ADC(fast) are the respective apparent diffusion coefficients (ADCs) of slow diffusing compartments (SDCs) and fast diffusing compartments (FDCs), and f(slow) and f(fast) the respective contributions to the signal intensity of SDC and FDC. RESULTS: In healthy subjects, FDC represents 74.3 +/- 3.1% of brain water, with ADC(fast) = (124.6 +/- 12.0) x 10(-5) mm(2)/s and ADC(slow) = (15.5 +/- 3.9) x 10(-5) mm(2)/s. In stroke, decreased FDC (49.1% +/- 10.9%; P = 1.05 x10(-5)) and increased ADC(slow) ([22.4 +/- 8.1] x 10(-5) mm(2)/s; P = 8.07 x 10(-3)) were observed, but ADC(fast) was not significantly changed ([135.6 +/- 25.7] x 10 (-5) mm(2)/s; P =.151). CONCLUSION: The restricted diffusion observed in the early stroke is mainly related to a redistribution of water from the FDC to the SDC.

Body Water↗

PubMed2004

[Diffusion behaviors of drugs in thermosensitive in situ gels].

AIM: To study the diffusion behaviors of drugs in thermosensitive in situ gels, and provide valuable information for designing such delivery systems. METHODS: A free diffusion model was used to evaluate the effects of concentration, the property of drugs, as well as the gel compositions on the diffusivity of drugs. RESULTS: Drug transport through the aqueous channels of the gel followed Fickian mechanism, and no significant influence on the diffusivity was observed when the drug concentration was lowered from 5% to 0.25%. The diffusion coefficients of propranolol, timolol maleate, and salbutamol sulfate were 0.91, 1.32, and 3.30 x 10(-6) cm2 x s(-1), respectively. The flux of hydrophilic drug was 3.6 fold faster than that of the lipophilic one implied the latter partitioned into the hydrophobic micellar core, and consequently the diffusion was retarded. The diffusivity was decreased with increased poloxamer and sodium hyaluronate concentration, due to the distorted aqueous channels and higher microviscosity. CONCLUSION: The result suggested that sustained release could be achieved for the thermosensitive in situ gel by incorporating lipophilic drug or increasing polymer concentration.

Albuterol↗

PubMedDate not supplied

Acute methotrexate neurotoxicity: findings on diffusion-weighted imaging and correlation with clinical outcome.

BACKGROUND AND PURPOSE: Acute lymphocytic leukemia (ALL) is a common malignancy of childhood treated with methotrexate (MTX), which is associated with acute neurotoxicity. We evaluated diffusion-weighted (DW) and conventional MR images in children with ALL and acute MTX-induced neurotoxicity, with clinical correlation. METHODS: Five patients aged 12-15 years underwent fluid-attenuated inversion recovery (FLAIR), T2-weighted fast spin-echo and gradient-echo, T1-weighted gadolinium-enhanced spin-echo, and DW imaging within 24 hours of symptom onset. Records were reviewed for the temporal relationship to MTX administration, strokelike symptoms, and neurologic outcome. RESULTS: Six strokelike events were temporally related to intrathecal MTX given 6-11 days before symptom onset. FLAIR images showed abnormal hyperintensity in the callosal splenium in one patient but were otherwise normal. Diffusion abnormalities were frontoparietal in three events and frontal in one; nonfluent aphasia was seen in all. Bilateral frontoparietal diffusion abnormalities were associated with bilateral upper-extremity weakness, right-sided hemiparesis, or left-sided hemiparesis (one patient each); one patient had mild facial droop. Unilateral precentral subcortical diffusion abnormality was associated with contralateral motor deficit and ipsilateral upper-extremity sensory loss. Strokelike symptoms resolved rapidly and were not associated with other signs of encephalopathy. Subsequent intrathecal MTX administration was not associated with recurrence in four patients. CONCLUSION: Diffusion abnormalities in acute MTX neurotoxicity indicated cerebral dysfunction but not necessarily overt structural injury to the cerebrum. Subsequent demyelination or gliosis could not be predicted on the basis of diffusion abnormalities. A single strokelike episode with diffusion abnormalities should not necessarily prompt modification of potentially curative chemotherapeutic regimens.

Acute Disease↗

PubMed2005

Distinct expression of adhesion molecules on skin fibroblasts from patients with diffuse and limited systemic sclerosis. A pilot study.

OBJECTIVE: . Systemic sclerosis (SSc) is characterized by excessive production of collagen and other components of the extracellular matrix (ECM) by fibroblasts. The ECM receptors, integrins and CD44 (hyaluronan receptor), play a key role in the homeostasis of connective tissue and may also have a role in the pathogenesis of fibrosis. We investigated the expression of integrins and CD44 on skin fibroblasts from patients with limited and diffuse SSc. METHODS: We studied 13 patients with SSc, 8 with limited SSc, and 5 with diffuse SSc, and 8 control subjects. Fibroblasts were isolated and cultured from biopsies taken from the lesional skin of the second finger of the left hand. Cell-surface expression of beta1, beta3, alpha1-alpha6, alphav integrins, and CD44 was evaluated by immunofluorescence and flow cytometry analysis. RESULTS: Fibroblasts from limited SSc showed significantly decreased expression of alpha2, alpha3, alpha4 integrins, while diffuse SSc fibroblasts had significantly reduced expression of alpha5, alphav integrins, and CD44. Diffuse SSc also had significantly increased expression of alpha6 integrin on fibroblasts. In controls, the expression of alpha4 and alpha5 correlated positively, while in limited and diffuse SSc it did not. CONCLUSION: This is the first study evaluating separately the expression of adhesion molecules on skin fibroblasts from limited and diffuse subsets of SSc. We detected a distinct pattern of expression with decrease of collagen and fibronectin receptors in limited SSc, and downregulation of fibronectin and hyaluronan receptors in diffuse SSc. These results suggest that changes of fibroblasts/ECM interactions and mechanisms underlying the pathogenesis of fibrosis in SSc may differ in the single subset of the disease.

Cells, Cultured↗

PubMed2006

Diffusion anisotropy changes in the brains of professional boxers.

BACKGROUND AND PURPOSE: Professional boxing may result in brain injury. We hypothesize that quantitative MR diffusion imaging may be useful in determining early white matter changes. METHODS: Forty-nine professional boxers (age 30 +/- 4.5 years) and 19 healthy control subjects (age 32 +/- 9.5 years) were imaged on a clinical 1.5T scanner. None of the subjects had neurologic disorder or deficit. The average diffusion constant (D(av)) and diffusion anisotropy (FA) were determined pixel by pixel. Regional diffusion measurements were done in the corpus callosum (CC) and internal capsule (IC). The whole brain diffusion constant (BD(av)) was also determined. Student t test was used to analyze the diffusion difference between boxers and the healthy control subjects. P < .05 was considered statistically significant. RESULTS: Of the 49 professional boxers, 42 had normal conventional MRIs. The remaining 7 boxers had abnormal MR imaging findings dominated by nonspecific white matter disease. There was a significant difference in diffusion and anisotropy measurements in all the boxers compared with the healthy control subjects. In the boxer group, BD(av) increased and FA decreased significantly in the CC and posterior limb of IC. The measured FA and D(av) inversely correlated in regions of CC and IC in boxers but not in healthy control subjects. BD(av) also robustly correlated with both FA and D(av) in the splenium of CC in boxers. CONCLUSION: Increased BD(av) and the decreased FA in the CC and IC may represent preclinical signs of subtle brain injury in professional boxers.

Adult↗

PubMedDate not supplied

Diffusion imaging of the human brain: a new pulse sequence application for a 1.5-T standard MR system.

We developed a new pulse sequence and investigated whether the anisotropic diffusion in the human brain can be detailed with a standard whole-body MR imager. Apparent diffusion coefficient maps were produced by the proposed sequence using a 1.5-T MR unit. The sequence employed simultaneous application of three orthogonal gradients to achieve an optimal signal attenuation for imaging the brain without any increase in echo time. The orientation of the effective diffusion-encoding gradient was off-axis. On the in vivo apparent diffusion coefficient maps of four healthy volunteers, white matter tracts (the internal capsule and the corpus callosum) and the cortical and deep white matter showed anisotropic diffusion. In the gray matter, such as basal ganglia and thalami, anisotropic diffusion was not observed. A typical whole-body imager can provide in vivo human brain diffusion images of clinical quality. This technique has promising implications for the evaluation of brain development and the diagnosis of degenerative diseases.

Adult↗

PubMed1991

Lateral diffusion of redox components in the mitochondrial inner membrane is unaffected by inner membrane folding and matrix density.

We report the first lateral diffusion measurements of redox components in normal-sized, matrix-containing, intact mitoplasts (inner membrane-matrix particles). The diffusion measurements were obtained by submicron beam fluorescence recovery after photobleaching measurements of individual, intact, rat liver mitoplasts bathed in different osmolarity media to control the matrix density and the extent of inner membrane folding. The data reveal that neither the extent of mitochondrial matrix density nor the complexity of the inner membrane folding have a significant effect on the mobility of inner membrane redox components. Diffusion coefficients for Complex I (NADH:ubiquinone oxidoreductase), Complex III (ubiquinol: cytochrome c oxidoreductase), Complex IV (cytochrome oxidase), ubiquinone, and phospholipid were found to be effectively invariant with the matrix density and/or membrane folding and essentially the same as values we reported previously for spherical, fused, ultralarge, matrix-free, inner membranes. Diffusion of proton-transporting Complex V (ATP synthase) appeared to be 2-3-fold slower at the greatest matrix density and degree of membrane folding. Consistent with a diffusion-coupled mechanism of electron transport, comparison of electron transport frequencies (productive collisions) with the theoretical, diffusion-controlled, collision frequencies (maximum collisions possible) revealed that there were consistently more calculated than productive collisions for all redox partners. Theoretical analyses of parameters for submicron fluorescence recovery after photobleaching measurements in intact mitoplasts support the finding of highly mobile redox components diffusing at the same rates as determined in conventional fluorescence recovery after photobleaching measurements in fused, ultralarge inner membranes. These findings support the Random Collision Model of Mitochondrial Electron Transport at the level of the intact mitoplast and suggest a similar conclusion for the intact mitochondrion.

Animals↗

PubMedDate not supplied

Ionic strength affects diffusive permeability to an inorganic phosphate ion of negatively charged dialysis membranes.

Electrolytes undergo electrostatic resistances in reaching membrane surfaces and passing through membrane pores when weakly charged dialysis membranes are used in hemodialysis treatments. Diffusive permeability to an electrolyte of weakly charged dialysis membranes depends upon the effective charge density of the membranes, which varies with ionic strength. The authors carried out dialysis experiments at a temperature of 310 K, with 32P-Na2HPO4 in aqueous NaCl and bovine serum, to obtain diffusive permeability to an inorganic phosphate ion of regenerated cellulose, and polymethylmethacrylate membranes of various fixed charge densities at varying ionic strengths ranging from 1.66 to 100 mol/m3. Diffusive permeability to an inorganic phosphate ion increased with ionic strength. Bovine serum, having an ionic strength of approximately 150 mol/m3, gave higher diffusive permeability to an inorganic phosphate ion. The internal structure of dialysis membranes, such as pore size, surface porosity, and tortuosity, also affects diffusive permeability. The electrolyte diffusion theory gives an effective charge density of -5.3 mol/m3 for the cellulosic membrane. In conclusion, ionic strength enhances diffusive permeability to an inorganic phosphate ion in both aqueous NaCl and bovine serum. Inorganic phosphate ion transport through negatively charged dialysis membranes depends upon the degree of dissociation of inorganic phosphate, the molecular size and valence of hydrated inorganic phosphate ion, the effective charge density and internal structure of the membrane, and ionic strength.

Animals↗

PubMed1988

Multidimensional diffusion modes and collision frequencies of cytochrome c with its redox partners.

We have determined the modes and rates of cytochrome c diffusion as well as the collision frequencies of cytochrome c with its redox partners at the surface of the isolated, mitochondrial inner membrane over a broad range (0-150 mM) of ionic strengths. Using fluorescence recovery after photobleaching, resonance energy transfer, and direct binding assay, we determined that the diffusion coefficient of cytochrome c is independent of its concentration and quantity bound to the inner membrane, that the distance of cytochrome c from the membrane surface increases with increasing ionic strength, and that there is no significant immobile fraction of cytochrome c on the membrane regardless of ionic strength. The rate of cytochrome c diffusion increases while its mode of diffusion changes progressively from lateral to three-dimensional with increasing ionic strength. At physiological ionic strength (100-150 mM), the diffusion of cytochrome c is three-dimensional with respect to the surface of the inner membrane with a coefficient of 1.0 x 10(-6) cm2/s, and little, if any cytochrome c is bound to the membrane regardless of its concentration. Furthermore, as ionic strength is raised from zero to 150 mM, the cytochrome ckd for the inner membrane increases, its mean occupancy time on the inner membrane to collide with a redox partner (tau) decreases, and its diffusion-based collision frequencies with its redox partners decrease. These data reveal the significance of both diffusion and concentration (affinity) of cytochrome c near the surface of the inner membrane in the control of the collision frequency of cytochrome c with its redox partners.

Algorithms↗

PubMedDate not supplied

In vivo measurement of water self diffusion in the human brain by magnetic resonance imaging.

A new pulse sequence for in vivo diffusion measurements by magnetic resonance imaging (MRI) is introduced. The pulse sequence was tested on phantoms to evaluate the accuracy, reproducibility and inplane variations. The sensitivity of the sequence was tested by measuring the self diffusion coefficient of water with different temperatures. This phantom study showed that the water self diffusion could be measured accurately and that the inplane deviation was less than +/- 10 per cent. Seven healthy volunteers were studied with a 10 mm thick slice through the lateral ventricles, clear differences between grey and white matter as well as regional differences within the white matter were seen. In two patients with infarction, alternations in water self diffusion were seen in the region of the infarct. Likewise, pronounced changes in brain water self diffusion were observed in a patient with benign intracranial hypertension. The results indicate that brain water self diffusion can be measured in vivo with reasonable accuracy. The clinical examples suggest that diffusion measurements may be clinically useful adding further information about in vivo MR tissue characterization.

Adolescent↗

PubMed1985

Linear diffusion of restriction endonucleases on DNA.

We have investigated the dependence of the rate of cleavage of DNA by EcoRI, HindIII, and BamHI on the chain length of the substrate. In order to keep the influence of flanking sequences and of nonspecific binding identical for all substrates we have carried out all experiments with the same plasmid DNA which had been digested previously with a variety of different restriction enzymes to give a set of substrates of different lengths. Our results show that depending on the buffer conditions long substrates are cleaved faster than small ones. We interpret these findings to mean that under certain conditions a linear diffusion of the enzymes on the DNA is involved in localizing the recognition sites. For EcoRI the mean diffusion length is approximately 1000 base pairs at 1 mM MgC12 which can be shown by diffusion theory to correspond to a linear diffusion coefficient of 5 X 10(-10) cm2 s-1. At 10 mM MgCl2 the linear diffusion of EcoRI is negligible and does not lead to a significant enhancement of the rate of site localization. In the presence of nonsaturating amounts of one of the prokaryotic histone-like protein Hu (NS 2) small and large DNA substrate are cleaved with identical rate by EcoRI indicating that other proteins bound to the DNA constitute a barrier across which linear diffusion cannot take place. We conclude that linear diffusion, albeit detectable under certain conditions in vitro, probably is of little importance for the process of site localization in vivo.

Binding Sites↗

PubMed1988

Glucocorticoid effects on lipid lateral diffusion and membrane composition in lipopolysaccharide-activated B-cell leukemia 1 cells.

We have investigated the effects of glucocorticoid treatment on lipid lateral diffusion and cholesterol:phospholipid ratios in the plasma membranes of the lipopolysaccharide (LPS)-responsive murine B-cell leukemia (BCL1). Exposure to LPS for 24 h at concentrations of 50 micrograms/ml, 100 micrograms/ml, and 250 micrograms/ml caused a 42% reduction in the lateral diffusion of the lipid probe 3,3'-dioctadecylindocarbocyanine iodide as measured by fluorescence photobleaching recovery techniques at 37 degrees C. In cells incubated with 50 micrograms/ml LPS, 3,3'-dioctadecylindocarbocyanine iodide diffusion is reduced to 2.2 x 10(-9) cm2s-1 compared to freshly isolated BCL1 cells where 3,3'-dioctadecylindocarbocyanine iodide diffused at a rate of 3.8 x 10(-9) cm2s-1. In BCL1 cells activated by LPS for 24 h and recultured with a pharmacological concentration of the synthetic glucocorticoid triamcinolone acetonide (TA, 10(-6) M) for 6 h, lipid lateral diffusion increased to 3.5 x 10(-9) cm2s-1. Concentrations of TA lower than 10(-6) M had no effect on lipid lateral diffusion. Six-h treatment with 10(-6) M TA had no effect on freshly isolated BCL1 cells (Time 0). However, lipid lateral diffusion increased in cells incubated 24, 48, and 72 h with LPS, and an additional 6 h with 10(-5) M TA suggested that activated BCL1 cells were more glucocorticoid sensitive than cells at Time 0. Plasma membrane cholesterol and phospholipid content, analyzed at 0 and 24 h, indicated that LPS activation was associated with a 7% increase in the cholesterol:phospholipid ratio in BCL1 membranes and that glucocorticoid treatment of these LPS-activated cells for 6 h decreased the membrane cholesterol:phospholipid ratio perhaps through inhibition of de novo cholesterol synthesis.

Animals↗