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At least 1,099 records · Page 61Linked to original sources
PubMed2004

Age-related changes of the dentate nuclei in normal adults as revealed by 3D fast low angle shot (FLASH) echo sequence magnetic resonance imaging.

The aim of the present study was to investigate age-related changes in iron-deposition in dentate nuclei using iron-induced susceptibility effects in magnetic resonance imaging. MR images from 74 healthy subjects (age range 20-68 years) were obtained using a three-dimensional (3D) T1-weighted fast low angle shot (FLASH) echo sequence. Signal intensities of the dentate nuclei and cerebellar white matter were bilaterally measured independently by three blinded investigators. The signal intensities of dentate nuclei were intraindividually normalised to the corresponding signal intensities of the cerebellar white matter of corresponding slices. Mean normalised signal intensities were correlated with age and compared between different age decades and gender. Intraclass correlation coefficients were high (dentate nuclei: 0.98, cerebellar white matter: 0.75) indicating sufficient interrater reliabilities for the determination of signal intensities. Bland-Altman analysis confirmed this finding. The normalised mean signal intensity of the dentate nuclei correlated inversely with age (r = -0.462, p < 0.0001). Comparison of age decades revealed that significant decreases took place between the third and fourth decade and to a lesser degree between the fourth and fifth decade. Moreover, variability of normalised mean signal intensities of the dentate nuclei increased significantly with age (r = 0.964, p = 0.008). There were no differences of the normalised mean signal intensities between genders. The present study revealed an age-dependent decrease of signal intensities in dentate nuclei most likely reflecting an age-dependent increase in dentate iron concentration. These age-dependent changes have to be taken into account in interpretation of disease related MR changes of cerebellar nuclei in patients with degenerative or acquired cerebellar ataxia.

Adult↗
PubMed1997

Troponin I phosphorylation does not increase the rate of relaxation following laser flash photolysis of diazo-2 in guinea-pig skinned trabeculae.

In vivo, two effects of beta-adrenergic stimulation in cardiac muscle are phosphorylation of troponin I and an increase in relaxation rate. In vitro, cardiac TnI can be phosphorylated by protein kinase A (PKA). We have used the technique of laser flash photolysis of the calcium chelator diazo-2 to investigate the effect of phosphorylation of TnI on the relaxation rate of skinned trabeculae from the guinea-pig at 12 degrees C. The fibres were phosphorylated by PKA, and double exponential curve fits of the average relaxation transients showed no significant difference between the rate constants of the phosphorylated and control cases. We conclude that TnI phosphorylation has no effect on the rate of relaxation in skinned trabeculae from the guinea-pig following diazo-2 photolysis.

Animals↗
PubMed2001

Double-flash, large-fraction radiation therapy as palliative treatment of malignant superior vena cava syndrome in the elderly.

Rapid control of symptoms is mandatory in cancer-induced superior vena cava syndrome (SVCS), but older patients often do not tolerate aggressive approaches. In order to maximize symptom relief and minimize treatment-related discomfort of aged patients in poor health we adopted a short-course, large-fraction radiation therapy (RT) schedule. Twenty-three consecutive patients aged over 70 who were suffering from solid-malignancy-related SVCS were enrolled. A total dose of 12 Gy was given in two 6-Gy fractions, 1 week apart, mainly in an out-patient setting. Completion of therapy to give up to 37-40 Gy was planned in the best-responding patients. Symptom relief was experienced by 8 patients as early as 4-5 days after the first fraction. The overall response rate was 87%. Despite some mild systemic side effects (chest pain, fever) reported by 5 patients (22%), overall toxicity was negligible. Short-course, double-flash RT stands as an effective and safe tool in the palliative treatment of malignant SVCS in older patients. Fractions larger than 6 Gy can be avoided in order to minimize side and toxic effects.

Aged↗
PubMed2001

The role of Gd-enhanced three-dimensional MRI fast low-angle shot (FLASH) in the evaluation of symptomatic lumbosacral nerve roots.

In the field of lumbar spine disorders, three-dimensional (3-D) magnetic resonance imaging (MRI) can clearly depict a lumbar nerve root from the distal region to the dorsal root ganglion. In this study, we used a gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) enhanced-three-dimensional (3-D) fast low-angle shot (FLASH) sequence when examining lumbosacral disorders. The subjects were 33 patients (14 men and 19 women) in whom lumbosacral neural compression had been diagnosed clinically. Twenty-one patients had lumbar disc herniation, 11 had lumbar spinal stenosis, and 1 had lumbar radiculopathy caused by rheumatoid arthritis. Five subjects with low back pain were also studied as a control group. In all patients and in all 5 of the controls, the dorsal root ganglion of every root was enhanced clearly. There was no root enhancement in the 5 controls. Enhancement of the symptomatic nerve roots, caused by compression, was found in 11 of the 33 patients. All 11 patients had radiculopathy, and muscle weakness was more frequent in patients with enhanced nerve roots than in those without enhancement. There was no enhancement of the cauda equina, even in the patients with cauda syndrome. The enhancement effect may reflect some pathological condition of the compressed nerve root and needs to be studied further.

Adolescent↗
PubMedDate not supplied

Flash visually evoked potentials in the newborn and their maturation during the first six months of life.

The aim of this paper has been to obtain normative data for the major components of the visually evoked potentials obtained by flash stimulus (F-PEV) in the newborn, and to analyse the evolution of these responses during the first 24 weeks of life. In order to do so, F-VEP were recorded in 109 normal full-term newborn infants. Fifty-five of these infants were also studied longitudinally at 4, 8, 12 and 24 weeks. We recorded responses in all newborns. A great morphological variability was observed. P2 was the only component present in all of these infants. Early components, which were always present from the fourth week of life on, were recorded in 34% of the newborns. There were significant differences according to waking/sleep state. At 24 weeks the most characteristic response was a triphasic waveform with clear negative-positive-negative components at 67.9, 110 and 158.3 ms. The morphological variability observed in the F-PEV of the newborn and the presence of early components in some cases, suggest differences in the maturation of the specific and unspecific visual system at birth. The study of these responses provides us with information about certain aspects of visual maturation. The relative stability of P2 response of the newborn and of the early negative components later on, made them the most useful components to be used in paediatric clinical work . The latency of P2 in the newborn is the parameter that showed lower variability, and therefore the most suitable one to establish normative data.

Evoked Potentials, Visual↗
PubMed2006

Congenital absence of optic chiasm: demonstration of an uncrossed visual pathway using monocular flash visual evoked potentials.

A 35 month old child was referred for electrophysiology testing with pendular nystagmus, corresponding head oscillations and reduced vision. Flash visual evoked potential (VEP) revealed large responses at the right occiput (but not the left occiput) from the right eye and similar large responses at only the left occiput from the left eye, indicating absent/deficient crossover at the chiasm. A magnetic resonance imaging (MRI) scan subsequently confirmed absence of the optic chiasm. There was no other evidence of midline brain defects. Her subsequent development to age 11 has been followed. The nystagmus has remained mainly horizontal but a torsional component was noted from age 5 years and described as see-saw at age 6 years. A small right esotropia was noted at 6 years and spectacles prescribed for low hypermetropic refractive error. Bilateral superior rectus recessions at age 7 years produced an improved head posture. Her visual acuity has remained stable at around 6/24 from age 4 years. No binocularity nor stereopsis has been demonstrated over subsequent visits.

Child, Preschool↗
PubMed2006

Studies on reaction of amino acids and triplet thioxanthone derivatives by laser flash photolysis.

Excitation of the thioxanthone derivatives (TXs), 2, 4-diethylthioxanthone (DETX) and 2-(2,3-epoxypropyloxy) thioxanthone (ETX) in acetonitrile/water mixture solution (1:1, v/v) upon 355 nm laser flash produced the triplet of TXs ((3)TXs(*)). Characteristic absorption spectra of (3)TXs(*)(590 nm) were recorded and rate constants of (3)TXs(*) quenched by O(2) and by its ground state were determined (9.8 x 10(9) M(-1) s(-1), 7.3 x 10(9) M(-1) s(-1) and 2.6 x 10(8) M(-1) s(-1), 2.2 x 10(8) M(-1) s(-1) respectively). The reactions of some amino acids oxidized by (3)TXs(*) were carried out. It has been found that tryptophan (Trp) and tyrosine (Tyr) can quench (3)TXs(*) via electron transfer process and related quenching rate constants were obtained. (3)TXs(*) induced protein damage was investigated using electrophoresis and significant levels of dimerisation were observed under aerobic and anaerobic conditions. The influence of photo-sensitizer's structure on photo-oxidation of amino acid and protein has been discussed.

Amino Acids↗
PubMed1978

Use of a xenon flash tube as the excitation source in a new slit-lamp fluorophotometer.

A new objective fluorophotometer measures fluorescein mass or concentration in the cornea or anterior chamber. The excitation source is a xenon flash tube that allows the measurement of fluorescence to be made rapidly and conveniently. The instrument is designed for use in clinical studies requiring quantitative measurements of fluorescence in the tears, the cornea, and the aqueous humor.

Animals↗
PubMed1991

Laser flash photolysis studies of the kinetics of reduction of ferredoxins and ferredoxin-NADP+ reductases from Anabaena PCC 7119 and spinach: electrostatic effects on intracomplex electron transfer.

The influence of electrostatic forces on the formation of, and electron transfer within, transient complexes between redox proteins was examined by comparing ionic strength effects on the kinetics of the electron transfer reaction between reduced ferredoxins (Fd) and oxidized ferredoxin-NADP+ reductases (FNR) from Anabaena and from spinach, using laser flash photolysis techniques. With the Anabaena proteins, direct reduction by laser-generated flavin semiquinone of the FNR component was inhibited by complex formation at low ionic strength, whereas Fd reduction was not. The opposite results were obtained with the spinach system. These observations clearly indicate structural differences between the cyanobacterial and higher plant complexes. For the complex formed by the Anabaena proteins, the results indicate that electrostatic forces are not a major contributor to complex stability. However, the rate constant for intracomplex electron transfer had a biphasic dependence on ionic strength, suggesting that structural rearrangements within the transient complex facilitate electron transfer. In contrast to the Anabaena complex, electrostatic forces are important for the stabilization of the spinach Fd:FNR complex, and changes in ionic strength had little effect on the limiting rate constant for intracomplex electron transfer. This suggests that in this case the geometry of the initial collisional complex is optimal for reaction. These results provide a clear illustration of the differing roles that electrostatic interactions may play in controlling electron transfer between two redox proteins.

Cyanobacteria↗
PubMed1992

Laser flash photolysis studies of electron transfer mechanisms in cytochromes: an aromatic residue at position 82 is not required for cytochrome c reduction by flavin semiquinones or electron transfer from cytochrome c to cytochrome oxidase.

The influence of an aromatic side chain at position 82 of yeast iso-1-cytochrome c on the kinetics of its electron transfer reactions has been investigated using laser flash photolysis methods to compare a series of site-specific mutant cytochromes in their reduction by free flavin semiquinone and in electron transfer from reduced cytochrome to bovine cytochrome c oxidase. Although small (approximately 10%) but significant differences are observed between some of the mutants (S82, Y82, I82) and wild-type (F82) or G82 cytochrome in the second-order rate constant for reduction by lumiflavin semiquinone, these do not correlate with side-chain aromaticity. In the reaction between the ferrocytochromes and cytochrome c oxidase, significantly larger deviations from exponentiality are found for those mutants having aliphatic residues at position 82 than for wild type or Y82. We interpret the nonexponential behavior in terms of multiple orientations of the cytochromes within the oxidase binding site; the extent to which this occurs is apparently influenced by the character of the residue at position 82. However, a comparison of the average rate constants for electron transfer to cytochrome oxidase for the various mutants reveals that all are closely comparable to WT, except for I82 which is significantly slower (approximately threefold). These results, combined with those obtained previously from steady-state kinetic and thermodynamic measurements, suggest that the observed differences among the mutants are due to alterations in the mode of binding of the cytochrome to the oxidase, rather than to a specific requirement for the presence of an aromatic group at position 82.

Animals↗
PubMed1975

Flash photolysis electron spin resonance studies of the electron acceptor species at low temperatures in photosystem I of spinach subchloroplast particles.

The light-induced electron spin resonance signals of Photosystem I spinach subchloroplast particles have been studied at approximately 6 degrees K. Using the technique of flash photolysis-electron spin resonance with actinic illumination at 647 nm, a kinetic analysis of the previously observed bound ferredoxin ESR signals was carried out. Signal I (P700+) exhibits a partial light-reversible behavior at 6 degrees K so it was expected that if the bound ferredoxin is the primary acceptor of Photosystem I, it should also exhibit a partial reversible behavior. However, none of the bound ferredoxin ESR signals showed any such light reversible behavior. A search to wider fields revealed two components which did exhibit the expected kinetic behavior. These components are very broad (about 80 G) and are centered at g equals to 1.75 and g equals to 2.07. These two components exhibit the expected characteristics of the primary electron acceptor. A model is presented to account for the reversible and irreversible photochemical changes in Photosystem I. The possible identity of the primary acceptor responsible for these two new components, is discussed in terms of the available information. The primary acceptor may be an iron-sulfur protein, but not of the type characteristic of the bound or water-soluble ferredoxins found so far in chloroplasts.

Chloroplasts↗
PubMed1976

Flash-induced absorption changes of the primary donor of photosystem II at 820 nm in chloroplasts inhibited by low pH or tris-treatment.

A comparative study is made, at 15 degrees C, of flash-induced absorption changes around 820 nm (attributed to the primary donors of Photosystems I and II) and 705 nm (Photosystem I only), in normal chloroplasts and in chloroplasts where O2 evolution was inhibited by low pH or by Tris-treatment. At pH 7.5, with untreated chloroplasts, the absorption changes around 820 nm are shown to be due to P-700 alone. Any contribution of the primary donor of Photosystem II should be in times shorter than 60 mus. When chloroplasts are inhibited at the donor side of Photosystem II by low pH, an additional absorption change at 820 nm appears with an amplitude which, at pH 4.0, is slightly higher than the signal due to oxidized P-700. This additional signal is attributed to the primary donor of Photosystem II. It decays (t 1/2 about 180 mus) mainly by back reaction with the primary acceptor and partly by reduction by another electron donor. Acid-washed chloroplasts resuspended at pH 7.5 still present the signal due to Photosystem II (t 1/2 about 120 mus). This shows that the acid inhibition of the first secondary donor of Photosystem II is irreversible. In Tris-treated chloroplasts, absorption changes at 820 nm due to the primary donor of Photosystem II are also observed, but to a lesser extent and only after some charge accumulation at the donor side. They decay with a half-time of 120 mus.

Chloroplasts↗
PubMed1976

Flash photolysis-electron spin resonance studies of photosystem I. A fast reduction of component of P-700+.

A 300 mus decay component of ESR Signal I (P-700+) in chloroplasts is observed following a 10 mus actinic xenon flash. This transient is inhibited by treatments which block electron transfer from Photosystem II to Photosystem I (e.g. 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), KCN and HgCl2). The fast transient reduction of P-700+ can be restored in the case of DCMU or DBMIB inhibition by addition of an electron donor couple (2,6-dichlorophenol indophenol (Cl2Ind)/ascorbate) which supplies electrons to cytochrome f. However, this donor couple is inefficient in restoring electron transport in chloroplasts which have been inhibited with the plastocyanin inactivators, KCN and HgCl2. Oxidation-reduction measurements reveal that the fast P-700+ reduction component reflects electron transfer from a component with Em = 375 +/- 10 mV (pH = 7.5). These data suggest the assignment of the 300-mus decay kinetics to electron transfer from cytochrome f (Fe2+) to P-700+, thus confirming the recent observations of Haehnel et al. (Z. Naturforsch. 26b, 1171-1174 (1971)).

2,6-Dichloroindophenol↗
PubMed1976

A flash photolysis ESR study of photosystem II signal IIvf, the physiological donor to P-680+.

In flash-illuminated, oxygen-evolving spinach chloroplasts and green algae, a free radical transient has been observed with spectral parameters similar to those of Signal II (g approximately 2.0045, deltaHpp approximately 19G). However, in contrast with ESR Signal II, the transient radical does not readily saturate even at microwave power levels of 200 mW. This species is formed most efficiently with "red" illumination (lambda less than 680 nm) and occurs stoichiometrically in a 1:1 ratio with P-700+. The Photosystem II transient is formed in less than 100 mus and decays via first-order kinetics with a halftime of 400-900 mus. Additionally, the t1/2 for radical decay is temperature independent between 20 and 4 degrees C; however, below 4 degrees C the transient signal exhibits Arrhenius behavior with an activation energy of approx. 10 kcal-mol-1. Inhibition of electron transport through Photosystem II by o-phenanthroline, 3-(3,4-dichlorophenyl)-1,1-dimethylurea or reduced 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone suppresses the formation of the light-induced transient. At low concentrations (0.2 mM), 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone partially inhibits the free radical formation, however, the decay kinetics are unaltered. High concentrations of 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (1-5 mM) restore both the transient signal and electron flow through Photosystem II. These findings suggest that this "quinoidal" type ESR transient functions as the physiological donor to the oxidized reaction center chlorophyll, P-680+.

Chlorella↗
PubMed1977

Flash-induced 515 nm absorbance change in chloroplasts with various granum contents.

The 515 nm absorbance change was studied in mesophyll and bundle sheath chloroplasts of maize, which contain different amounts of grana. The amplitude of the 515 nm signal (induced by 3 micro seconds flashes repeated at 4 s intervals) has shown a correlation with the granum content of the samples. However, upon addition of N-methylphenazonium methosulphate the 515 nm signal became independent of the amount of grana: in agranal thylakoids a large pool of silent Photosystem I was activated and, as a result, the amplitude of the 515 nm signal of agranal chloroplasts increased to the level exhibited by granal chloroplasts. These data show that the 515 nm absorbance change is not limited to small closed vesicles like grana, but in the presence of suitable electron donors single lamellae of bundle sheath chloroplasts can also be active.

Chloroplasts↗
PubMed1977

Low-temperature flash photolysis studies of cytochrome oxidase and its environment.

The CO-binding kinetics of cytochrome a3, in isolated, detergent-solubilized cytochrome oxidase have been studied by flash photolysis over wide ranges of CO concentration and temperature. The results strongly suggest that CO has an intermediate bound state in its path to the final bound state at the heme iron. In the temperture range 230-273 K in frozen aqueous solutions, the recombination rates depend upon CO concentration; at low CO concentrations the kinetics are biphasic. The rate of the faster process depends upon the detergent concentration, that of the slower process upon the salt concentration. In addition, the faster process depends upon the amount of CO photodissociated. It is concluded that the cytochrome oxidase molecules are aggregated in regions that contain detergent and possibly some lipids. The regions retain considerable fluid character well below the macroscopic freezing point of the solution. The faster phase of the recombination is interpreted as the rebinding of CO molecules that remain in the fluid region after photodissociation. The slower phase would then be due to the migration of some dissociated CO out into surrounding frozen solvent. The non-Arrhenius behavior of both phase probably represents partial melting of the medium; preliminary NMR measurements of mobile protons support this hypothesis. Many of the kinetic features described here are also seen in mitochondria; thus the detergent-solubilized cytochrome oxidase may be a useful model system for the ligand-binding behavior of the enzyme in the mitochondrial membrane.

Carbon Monoxide↗
PubMed1977

Cytochrome f and plastocyanin kinetics in Chlorella pyrenoidosa. I. Oxidation kinetics after a flash.

P-700, plastocyanin and cytochrome f redox kinetics were measured after one flash, using dark-adapted Chlorella in the presence of hydroxylamine and 3(3,4-dichlorophenyl)-1,1-dimethylurea. Plastocyanin becomes increasingly oxidized with a half-time of 70 microseconds, then undergoes reduction with a half-time of 7ms. Cytochrome f oxidation has a sigmoidal time-course and a half-time of 100 microseconds. Its redution exhibits a half-time of 4 ms. These results are interpreted in a linear scheme: (formula: see text). An equilibrium constant of 2 between cytochrome f and plastocyanin (PC), which contrasts with the large equilibrium constant between PC and P-700 is computed. The presence of cytochrome b6 in a cyclic path around Photosystem I is confirmed under these conditions.

Chlorella↗
PubMed1977

Flash induced fluorescence kinetics in chloroplasts in the 20 microseconds-100 s time range in the presence of 3(3,4-dichlorophenyl)-1,1-dimethylurea. Effects of hydroxylamine.

Flash induced variations of the fluorescence yield have been studied at 2 degrees C over a long time range (at 1 microseconds and from 20 microseconds to 3 min) in chloroplasts in the presence of 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) with or without addition of hydroxylamine. 1. In the presence of DCMU, a polyphasic rise is observed. A first fast rise (less than 1 microseconds) is ascribed to the transfer of the positive charge from the primary Photosystem II donor Chl to a secondary donor Y. Two hypotheses are proposed to interpret the existence of the subsequent slower increase (t1/2 approximately equal to 70 microseconds) which then follows the initial fast rise. 2. The effects or various hydroxylamine concentrations have been studied with a sufficient incubation time to inactivate the secondary donors Y and Z. This inactivation leads to a complete inhibition of the ability to emit oxygen. Under these conditions, the initial fast rise (less than 1 microseconds) is inhibited as shown by den Haan, G.A., Duysens, L. N. M. and Egberts, D. J. N. (1974) Biochim. Biophs. Acta 368, 409-421, and the oxidized Chl+ is reduced by an auxiliary donor D. The slow fluorescence rise observed after destruction of Y and Z has a similar kinetic behaviour to that observed in the presence of DCMU only and is polyphasic. In the presence of 10 mM hydroxylamine, the constant rate of the back reaction k1 between Chl+ and the primary acceptor Q- is estimated to be approx. (135 microseconds)-1 while the transfer of the positive charge from Chl+ to D has a rate constant k2 of approx. (105 microseconds)-1. 3. In the presence of hydroxylamine concentrations higher than 10 mM, there appears a rise in the 1-20 microseconds range ascribed to a direct reduction of oxidized Chl+ by hydroxylamine. 4. In chloroplasts treated with 10 mM hydroxylamine for 15 min and washed afterwards, the rate constant k3 of the back reaction between D+ and Q- is estimated to be approx. (100 ms)-1 which leads to a value of about 700 for the equilibrium constant between Chl and D. Hydroxylamine added under these conditions is able to reduce D+. The rate constant k4 of this reduction is estimated to be (350 ms)-1 in 0.1 mM hydroxylamine.

Chlorophyll↗