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PubMed1979

The decreased membrane fluidity of in vivo aged, human erythrocytes. A spin label study.

The decreased membrane fluidity of the in vivo aged, human erythrocytes is found, by monitoring the electron paramagnetic resonance (EPR) spectra of fatty acid spin labels incorporated into the membrane. In addition, the decreased cell sizes and the decreased cholesterol and phospholipids contents, without significant changes of the quantity of the membrane proteins, also the decrease of ATP and 2,3-diphosphoglycerate and the increase of ADP and AMP, in the aged cells, were observed. Further the functional impairments of the aged cells, i.e. the increased oxygen affinity and the decreased deformability, were shown. On the basis of these quantitative data, the alteration of the protein-lipid organization, due to decreased lipid/protein ratio, the modified protein-lipid interaction and/or the influences of the diminished ATP content, is suggested to contribute towards the decreased membrane fluidity of the in vivo aged erythrocytes.

Adenine Nucleotides↗
PubMed1985

A spin-label study on human high density lipoprotein.

Human plasma high density lipoproteins (HDL) have been labeled with N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)maleimide (NEM-TEMPO). The spin-labeled HDL exhibited an ESR spectrum containing signals of both strongly immobilized and weakly immobilized components by the reaction with a high concentration of NEM-TEMPO, while an ESR spectrum containing only signals of a strongly immobilized component range between 4 degrees C and 37 degrees C, the signal height of the strongly immobilized component exhibited reversible temperature-dependent changes, whereas that of the weakly immobilized component changed irreversibly at temperatures above 25 degrees C. The activation energy of the irreversible change was estimated to be 26 kcal per mol. The strongly immobilized component was derived from NEM-TEMPO which modified apolipoprotein A-I covalently, while the weakly immobilized component was derived from NEM-TEMPO noncovalently bound to HDL. The rate of binding of NEM-TEMPO to either the strongly binding or weakly binding sites and the number of the strongly binding sites in apolipoprotein A-I were estimated to be 125 M-1.day-1 and 1.78, respectively. The binding of NEM-TEMPO to the strongly binding sites was suppressed greatly by pretreatment of HDL with 2,4,6-trinitrobenzene sulfonic acid (TNBS). The slow reaction and suppression with TNBS suggest that NEM-TEMPO binds to some amino acid residue, probably a lysine residue, in apoprotein A-I. The strongly immobilized and weakly immobilized components were reduced almost completely by ascorbate at the same rate, 0.048 min-1 at pH 7.4 and at 4 degrees C.

Ascorbic Acid↗
PubMed1975

Manganese (II) And spin-labeled uridine 5'-diphosphate binding to bovine galactosyltransferase.

The kinetically observed Mn(II) activation as well as inhibition has been clarified for bovine galactosyltransferase. An electron spin resonance (ESR) titration of MnCl2 with galactosyltransferase alone at pH 8.0 clearly shows the existence of at least two metal ion binding sites with microscopic dissociation constants of 0.84 +/- 0.1 and 9.0 +/- 1.0 mM, respectively. The second site corresponds with either published kinetic constant for Mn(II) of 8.5 mM (inhibition) or 3.40 mM (activation). The contribution of the binary complex Mn(II)-UDPGal is of lesser significance, as concluded by its ESR measured Kdiss of 14.5 +/- 1.1 mM at pH 8.0. A spin-labeled inhibitor analog of UDPgalactose, UDP-4-O-(2,2,6,6-tetramethyl-4-piperidinyl-1-oxy), or UDP-R, was synthesized as a competitive inhibitor for UDPGal. It was shown from inhibition kinetics to be almost as potent an inhibitor as UDPGlu. The Ki values at pH 8.0 in the N-acetyllactosamine and lactose reactions were 0.38 +/- 0.04 and 0.63 +/- 0.06 mM, respectively, as compared with 0.10 +/- 0.01 and 0.094 +/- 0.009 mM for UDPGlu. An ESR titration of UDP-R with galactosyltransferase at pH 8.0 yielded direct physical dissociation constants of 0.40 +/- 0.07 and 0.53 +/- 0.08 mM in the absence and presence of alpha-lactalbumin, respectively. No other substrates (glucose of N-acetylglucosamine) nor Mn(II) were present.

Animals↗
PubMed1983

Spin label measurement of platelet alignment in a clot induced by isometric tension.

A spin label technique was applied to examine the alignment of platelet membranes in the platelet-fibrin clot. The ESR spectrum of the clot in the control experiment was typical of isotropically oriented membranes, while the ESR spectrum of the clot which was kept isometric was quite different from that of the control experiment. These spectra were simulated with a computer and explained to indicate that the shape of platelets in the clot was transformed to a cylindrical form under the isometric tension so that axes of all membrane cylinders were directed parallel to the generated force.

Animals↗
PubMed2004

Electron paramagnetic resonance studies of magnetically aligned phospholipid bilayers utilizing a phospholipid spin label.

X-band electron paramagnetic resonance (EPR) spectroscopy was used to study the structural and dynamic properties of magnetically aligned phospholipid bilayers utilizing a variety of phosphocholine spin labels (PCSL) as a function oftemperature. 1-Palmitoyl-2-[n-(4,4-dimethyloxazolidine-N-oxyl)stearoyl]-sn-glycero-3-phosphocholine (n-PCSL) in which a nitroxide group was attached to the different acyl chain positions of the phospholipid (n = 5, 7, 12, and 14) were used as an EPR spin probe to investigate magnetically aligned phospholipid bilayers from the plateau (near to the headgroup) region to the end of the acyl chain (center of the bilayers). The addition of certain types of paramagnetic lanthanide ions changes the overall magnetic susceptibility anisotropy tensor of the bicelles, such that the bicelles flip with their bilayer normal either parallel or perpendicular to the magnetic field. The present study reveals for the first time that, in the case of the n-PCSL, the bilayer normal is aligned parallel and perpendicular to the magnetic field in the presence of lanthanide ions having positive delta(chi) (e.g., Tm3+) and negative delta(chi) (e.g., Dy3+), respectively. The magnetic alignment of the bilayers and the corresponding segmental molecular order parameter, S(mol), were investigated as a function of the temperature. The S(mol) values decrease in the following order, 5-PCSL > 7-PCSL > 12-PCSL > 14-PCSL, for the magnetically aligned phospholipid bilayers. Also, the variable temperature study indicates that, by increasing the temperature, the order parameters S(mol) decreased for all the n-PCSLs. The results indicate that magnetically aligned phospholipid bilayers represent an excellent model membrane system for X-band EPR studies.

Electron Spin Resonance Spectroscopy↗
PubMed1980

Spin-label studies of erythrocytes in myotonic dystrophy: no increase in membrane fluidity.

The basic defect in myotonic dystrophy is thought to involve muscle cell membranes. Butterfield and associates have recently presented electron spin resonance data that suggest increased fluidity of erythrocyte membranes in patients with myotonic dystrophy. We studied erythrocytes from 11 patients with myotonic dystrophy and 14 age-matched controls, using spin-labeled fatty acid and ester probes. Despite attempts to reproduce the previously reported experimental conditions exactly, we found no significant differences in the electron spin resonance spectra of erythrocytes from normal and myotonic dystrophy subjects. These findings do not provide evidence of increased erythrocyte membrane fluidity in myotonic dystrophy; they fail to support the concept of an intrinsic defect of the lipid membrane in this disorder.

Adult↗
PubMed2006

Physiological noise reduction for arterial spin labeling functional MRI.

Three methods for the reduction of physiological noise in arterial spin labeling (ASL) functional magnetic resonance imaging (fMRI) are presented and compared. The methods are based upon a general linear model of the ASL measurement process and on a previously described retrospective image-based method (RETROICOR) for physiological noise reduction in blood oxygenation level dependent fMRI. In the first method, the contribution of physiological noise to the interleaved control and tag images that comprise the ASL time series are assumed to be equal, while in the second method this assumption is not made. For the third method, it is assumed that physiological noise primarily impacts the perfusion time series obtained from the filtered subtraction of the control and tag images. The methods were evaluated using studies of functional activity in the visual cortex and the hippocampal region. The first and second methods significantly improved statistical performance in both brain regions, whereas the third method did not provide a significant gain. The second method provided significantly better performance than the first method in the hippocampal region, whereas the differences between methods were less pronounced in visual cortex. The improved performance of the second method in the hippocampal region appears to reflect the relatively greater effect of cardiac fluctuations in this brain region. The proposed methods should be particularly useful for ASL studies of cognitive processes where the intrinsic signal to noise ratio is typically lower than for studies of primary sensory regions.

Adult↗
PubMed1981

Spin-label studies of the lipid and protein components of erythrocyte membranes. A comparison of electron paramagnetic resonance and saturation transfer electron paramagnetic resonance methods.

We have used both a protein spin label and a lipid spin probe to study some of the slow motions of proteins and of lipids, respectively, in intact erythrocyte membranes. Three electron paramagnetic resonance (EPR) methods, conventional (V1) EPR, second harmonic out-of-phase absorption saturation transfer (ST) EPR (V'2), and first harmonic out-of-phase dispersion ST EPR (U'1) were used to compare the experimental methods and spectral sensitivities with different kinds of molecular motions in human erythrocyte membranes under different experimental conditions. The results show that the V'2 display is relatively more sensitive to the protein motion, while the U'1 display appears more sensitive to the lipid motions, and the V'2 display is substantially more convenient to obtain than the U'1 display.

Electron Spin Resonance Spectroscopy↗
PubMed1975

Spin label studies on rat liver plasma membrane: calcium effects on membrane fluidity.

Spin-labeled stearic acid probes were incorporated into rat liver plasma membrane purified by a zonal centrifugation procedure. Temperature effects on the order parameter calculated from the spectra indicated the possible presence of a membrane phase transition at 20 degrees, in agreement with earlier studies in other systems. Addition of Ca2+ (1.96 mM) at 37 degrees increased the order parameter by 6.0 +/- 0.7%, suggesting a Ca2+-mediated decrease in membrane fluidity.

Animals↗
PubMed1998

Multislice imaging of quantitative cerebral perfusion with pulsed arterial spin labeling.

A method is presented for multislice measurements of quantitative cerebral perfusion based on magnetic labeling of arterial spins. The method combines a pulsed arterial inversion, known as the FAIR (Flow-sensitive Alternating Inversion Recovery) experiment, with a fast spiral scan image acquisition. The short duration (22 ms) of the spiral data collection allows simultaneous measurement of up to 10 slices per labeling period, thus dramatically increasing efficiency compared to current single slice acquisition protocols. Investigation of labeling efficiency, suppression of unwanted signals from stationary as well as intraarterial spins, and the FAIR signal change as a function of inversion delay are presented. The assessment of quantitative cerebral blood flow (CBF) with the new technique is demonstrated and shown to require measurement of arterial transit time as well as suppression of intraarterial spin signals. CBF values measured on normal volunteers are consistent with results obtained from H2O15 positron emission tomography (PET) studies and other radioactive tracer approaches. In addition, the new method allows detection of activation-related perfusion changes in a finger-tapping experiment, with locations of activation corresponding well to those observed with blood oxygen level dependent (BOLD) fMRI.

Artifacts↗
PubMed2006

Comparison of spatial and temporal pattern for fMRI obtained with BOLD and arterial spin labeling.

Functional magnetic resonance imaging (fMRI) is presently either performed using blood oxygenation level-dependent (BOLD) contrast or using cerebral blood flow (CBF), measured with arterial spin labeling (ASL) technique. The present fMRI study aimed to provide practical hints to favour one method over the other. It involved three different acquisition methods during visual checkerboard stimulation on nine healthy subjects: 1) CBF contrast obtained from ASL, 2) BOLD contrast extracted from ASL and 3) BOLD contrast from Echo planar imaging. Previous findings were replicated; i) no differences between the three measurements were found in the location of the activated region; ii) differences were found in the temporal characteristics of the signals and iii) BOLD has significantly higher sensitivity than ASL perfusion. ASL fMRI was favoured when the investigation demands for perfusion and task related signal changes. BOLD fMRI is more suitable in conjunction with fast event related design.

Arteries↗
PubMed2001

Effects of bilirubin molecular species on membrane dynamic properties of human erythrocyte membranes: a spin label electron paramagnetic resonance spectroscopy study.

Unconjugated bilirubin is a neurotoxic pigment that interacts with membrane lipids. In this study we used electron paramagnetic resonance and the spin labels 5-, 7-, 12-, and 16-doxyl-stearic acid (DSA) to evaluate the depth of the hydrocarbon chain at which interaction of bilirubin preferentially occurs. In addition, we used different pH values to determine the molecular species involved. Resealed right-side-out ghosts were incubated (1-60 min) with bilirubin (3.4-42.8 microM) at pH 7.0, 7.4, and 8.0. Alterations of membrane dynamic properties were maximum after 15 min of incubation with 8.6 microM bilirubin at pH 7.4 and were accompanied by a significant release of phospholipids. Interestingly, concentrations of bilirubin up to 42.8 microM and longer incubations resulted in the elution of cholesterol and further increased that of phospholipids while inducing less structural alterations. Variation of the pH values from 8.0 to 7.4 and 7.0, under conditions of maximum perturbation, led to a change from an increased to a diminished polarity sensed by 5-DSA. Conversely, a progressive enhancement in fluidity was reported by 7-DSA, followed by 12- and 16-DSA. These results indicate that bilirubin while enhancing membrane lipid order at C-5 simultaneously has disordering effects at C-7. Furthermore, recovery of membrane dynamics after 15 min of bilirubin exposure along with the release of lipids is compatible with a membrane adaptive response to the insult. In addition, our data provide evidence that uncharged diacid is the species primarily interacting with the membrane as perturbation is favored by acidosis, a condition frequently associated with hyperbilirubinemia in premature and severely ill infants.

Bilirubin↗
PubMedDate not supplied

In vivo quantitative mapping of cardiac perfusion in rats using a noninvasive MR spin-labeling method.

Measurement of myocardial perfusion is important for the functional assessment of heart in vivo. Our approach is based on the modification of the longitudinal relaxation time T1 induced by magnetic spin labeling of endogenous water protons. Labeling is performed by selectively inverting the magnetization within the detection slice, and longitudinal relaxation is measured using a fast gradient echo MRI technique. As a result of blood flow, nonexcited spins enter the detection slice, which leads to an acceleration of the relaxation rate. Incorporating this phenomenon in a mathematical model that describes tissue as two compartments yields a simple expression that allows the quantification of perfusion from a slice-selective and a global inversion recovery experiment. This model takes into account the difference between T1 in blood and T1 in tissue. Our purpose was to evaluate the feasibility and reproducibility of this technique to map quantitatively myocardial perfusion in vivo in rats. Quantitative maps of myocardial blood flow were obtained from nine rats, and the reproducibility of the technique was evaluated by repeating the whole perfusion experiment four times. Evaluation of regions of interest within the myocardium yielded a mean perfusion value of 3.6 +/- .5 ml x min(-1) x g(-1) over all animals, which is in good agreement with previously reported literature values.

Animals↗
PubMed1990

Spin-labelling studies of the interaction of 9-amino-1,2,3,4-tetrahydroacridine (THA), a proposed drug for the treatment of Alzheimer's disease, with erythrocyte membranes.

ESR spin labels specific for skeletal proteins or cell-surface sialic acid have been used to monitor the interaction of 9-amino-1,2,3,4-tetrahydroacridine (THA) and its structural analogs with human erythrocyte membranes. The results suggest that THA significantly increases skeletal protein-protein interactions and may secondarily alter the physical state of the opposite side of the membrane. The fully aromatic analog of THA, 9-aminoacridine, showed even more pronounced effects on skeletal proteins than did THA. These results are discussed in relation to possible interaction sites of THA in erythrocyte ghosts and to potential mechanisms by which THA reportedly increases mental function of victims of Alzheimer's disease.

Alzheimer Disease↗
PubMed2006

Perfusion imaging of meningioma by using continuous arterial spin-labeling: comparison with dynamic susceptibility-weighted contrast-enhanced MR images and histopathologic features.

PURPOSE: The goal of the present study was to determine the utility of continuous arterial spin labeling (CASL) for characterization of meningioma by MR perfusion imaging and to compare these results with those obtained from the T2 dynamic susceptibility contrast (T2DSC) method and from histopathologic examination. METHODS: Twenty-one cases of meningiomas were examined at 1.5T. CASL perfusion imaging was implemented on the basis of multisection single-shot echo-planar imaging with velocity-driven adiabatic spin-inversion preparation. T2DSC perfusion imaging was also performed by using a double-echo spoiled gradient echo sequence in a section containing the tumor. By focusing on the regions of interest, maps of % signal intensity change and cerebral blood flow (CBF) were determined from CASL and cerebral blood volume (CBV). CBF and mean transit time (MTT) were obtained from T2DSC. The microvessel area (MVA) was determined from specimens immunostained with anti-CD31 in 14 cases by measuring the total amount of staining in each histologic section. Linear regression analysis was performed for rCBF values from both perfusion methods and for % signal intensity change and MVA. RESULTS: There was a significant correlation between CBF values determined from both perfusion methods (r(2) = 0.73; P < .001); however, the slope from T2DSC to CASL was less than unity, likely because of the different vascular weighting used for each method. There was also a significant correlation between CASL-% signal intensity change and MVA determined by histopathology (r(2) = 0.91; P < .00001). Perfusion values were the greatest for angiomatous meningioma and lowest for fibrous meningioma when using either perfusion method. CONCLUSIONS: CASL and T2DSC perfusion methods are comparable in the characterization of meningiomas. Further, CASL is of use in assessing tumor microcirculation.

Adult↗
PubMed1972

Manganous ion as a spin label in studies of mitochondrial uptake of manganese.

Manganous ion (Mn(2+)) has been used as a spin label for studies of divalent cation uptake by rat liver mitochondria. Spin exchange, observed in the electron paramagnetic resonance (EPR) spectrum of a fraction of the transported Mn(2+), shows that this fraction is bound in regions of high local concentration within the mitochondria. The average separation of manganese ions in that fraction is estimated to be 4.0 +/-0.6 A at the time of greatest concentration.

Animals↗
PubMed1979

Chromium oxalate: a new spin label broadening agent for use with thylakoids.

Potassium tris(oxalato)chromate(III) trihydrate (chromium ixalate) has been shown to be a more useful broadening agent than potassium ferricyanide for the spin label 2,2,6,6-tetramethylpiperidine-N-oxyl-4-amine (Tempamine) in thylakoid suspensions. Our data show that chromium oxalate is less permeable than ferricyanide, does not inhibit thylakoid electron transport or photophosphorylation, and is not photoreduced by thylakoids.

Chloroplasts↗