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PubMed1982

Exchange thresholds for long-wavelength incremental flashes.

Thresholds of 1-deg, 200-msec, 641-nm foveal test flashes rise after an exchange of II5-equated 536- and 626-nm fields, taking about 30 sec to recover. Silent substitution (no rise of threshold after the exchange) occurs, however, if these fields are alternated during adaptation. Thresholds for a 1-deg, 20-msec test rise similarly after an exchange but recover in only 0.5 sec and are not influenced by alternation of the 536- and 626-nm fields. These results can be accounted for if the 641-nm tests are detected not through pathways controlled by long-wavelength cones alone but through nonopponent (20-msc) and opponent (200-msec) pathways whose sensitivities may be reduced by transient inputs from other cones.

Adaptation, Physiological↗
PubMed2006

Atmospheric flash injuries in roe deer (Capreolus capreolus).

The pathological and histopathological examination of two female roe deer found dead after a severe thunderstorm is described. One of the two roe deer was killed by a direct hit of atmospheric flash, while the other animal, lying 1.5 m from the first one, died as a consequence of ground current strike. The major part of the coat and skin of the animal that was killed by a direct hit was covered with scorched streaks. The trachea and bronchi of both animals contained a considerable amount of aspirated light-red foam. Necropsy revealed diffuse haemorrhages over the epicardium of the right atrium with a diameter of 1 millimetre. The liver and the kidney exhibited severe congestion.

Animals↗
PubMed2000

A laser flash photolysis and pulse radiolysis study of primary photochemical processes of flumequine.

The 355 nm laser flash photolysis of argon-saturated pH 8 phosphate buffer solutions of the fluoroquinolone antibiotic flumequine produces a transient triplet state with a maximum absorbance at 575 nm where the molar absorptivity is 14,000 M(-1) cm(-1). The quantum yield of triplet formation is 0.9. The transient triplet state is quenched by various Type-1 photodynamic substrates such as tryptophan (TrpH), tyrosine, N-acetylcysteine and 2-deoxyguanosine leading to the formation of the semireduced flumequine species. This semireduced form has been readily identified by pulse radiolysis of argon-saturated pH 8 buffered aqueous solutions by reaction of the hydrated electrons and the CO2*- radicals with flumequine. The absorption maximum of the transient semireduced species is found at 570 nm with a molar absorptivity of 2,500 M(-1) cm(-1). In argon-saturated buffered solutions, the semireduced flumequine species formed by the reaction of the flumequine triplet with TrpH stoichiometrically reduces ferricytochrome C (Cyt Fe3+) under steady state irradiation with ultraviolet-A light. In the presence of oxygen, O2*- is formed but the photoreduction of Cyt Fe3+ by O2*- competes with an oxidizing pathway which involves photo-oxidation products of TrpH.

Anti-Infective Agents↗
PubMed2002

Effect of aggregation on bacteriochlorin a triplet-state formation: a laser flash photolysis study.

Bacteriochlorin a (BCA) is a potential photosensitizer for photodynamic therapy of cancer. It has been shown previously that the photoefficiency of the dye is mainly dependent on singlet oxygen (1O2) generation. Nanosecond laser flash photolysis was used to produce and to investigate the excited triplet state of the dye in methanol, phosphate buffer and dimiristoyl-L-alpha-phosphatidylcholine (DMPC) liposomes. The transients were characterized in terms of their absorption spectra, decay kinetics, molar absorption coefficients and formation quantum yield of singlet-triplet intercrossing. The lifetime of the BCA triplet state was measured at room temperature. The triplet-state quantum yield is quite high in methanol (0.7) and in DMPC (0.4) but only 0.095 in phosphate buffer. In the last case, BCA is in a monomer-dimer equilibrium, and the low value of the quantum yield observed was ascribed to the fact the triplet state is only formed by the monomers.

Buffers↗
PubMedDate not supplied

Primary photochemical processes of the phototoxic neuroleptic cyamemazine: a study by laser flash photolysis and steady-state irradiation.

The photophysical and photochemical properties of the UV-A-absorbing phototoxic drug cyamemazine (CMZ) (2-cyano-10-(3-[dimethylamino]-2-methyl-propyl)-phenothiazine) have been investigated in neutral buffered aqueous solutions. The transient absorbances of the hydrated electrons, of the first excited triplet state (3CMZ*) with a characteristic absorption band peaking at 420 nm and of the radical cation (*CMZ+) (maximum absorbance at 500 nm) have been observed by 355 nm laser flash spectroscopy of deaerated solutions. All these transient species are formed by monophotonic processes and react with oxygen. Bimolecular reaction rate constants of *CMZ+ and 3CMZ* with O2 are 2 x 10(7) M(-1) s(-1) and 4 x 10(9) M(-1) s(-1), respectively. The 3CMZ* reacts only sluggishly (reaction rate constant, 9 x 10(6) M(-1) s(-1)) with tryptophan chosen as a Type-I photodynamic substrate. Steady-state irradiations with 365 nm light demonstrate that CMZ is rapidly photolyzed (quantum yield, 0.04) in O2-saturated solutions leading to oxidation of the sulfur atom and of the side-chain nitrogen of CMZ. This photoproduct (2-cyano-10-(3-[dimethylamino, N-oxide]-2-methyl-propyl)-5-oxide-phenothiazine), is a good Type-I and Type-II photodynamic photosensitizer producing singlet oxygen in high yield (approximately 0.45) and could play a major role in the phototoxicity of CMZ.

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

Laser flash photolysis in a O3/Cl2 mixture at 266 nm in a very low-pressure flow system.

The laser flash photolysis in a very low-pressure flow system with mass spectrometry detection technique was developed for the study of oxidation reactions of chlorofluorocarbons. In this work, we have studied the UV photolysis of O3 in the presence of Cl2 at room temperature, which presents two catalytic cycles of O3 depletion with efficiencies dependent on the partial pressures in the photoreactor. The ozone dissociation was initiated with fourth harmonic pulses of a Nd:YAG laser. The detection of the reactants and the final and intermediate reaction products was performed with real-time mass spectrometry. The variations of the O3, Cl2 and ClO concentration were measured. The equations system associated to a proposed kinetic scheme was solved numerically and excellent agreement with the experimental results was obtained. The results from this work allowed the determination of the wall loss rates of the O(1D), Cl and ClO radicals.

Journal Article↗
PubMedDate not supplied

Comprehensive photochemistry and photophysics of land- and marine-based beta-carbolines employing time-resolved emission and flash transient spectroscopy.

The photophysical and photochemical behavior of Norharmane (Norh), Harmane (Hara) and Harmine (Hari) and their cations have been examined as a function of the nature of the solvent. Time-resolved emission in nonprotic polar solvents showed fluorescence for all and also phosphorescence for Hari. All emissions were assigned as those of the neutral molecules. Norh and Hari showed fluorescence of both the neutral and the cation in methanol as well as phosphorescence of the neutral while Hari also had fluorescence of the zwitter ion. In ethanol, Norh and Hari displayed fluorescence and phosphorescence of the neutral. The ground-state cations of Norh and Hari exhibited fluorescences of the cation and Hari also had a phosphorescence (cation). The flash transient spectra in nonprotic solvents of all three carbolines had long-lived triplet transients only of the neutral. Triplet and singlet oxygen yields were quite high, 0.31-0.40. Direct excitation of any of the cations gave only the cation triplet. The triplet yields of the cations appear to be low (0.01-0.10 range). Theoretical calculations were done relative to location of triplet states. Some new information will be reported on other naturally occurring differently substituted marine-based beta-carbolines. The impact of all of the foregoing observations on the photosensitizing potential of all compounds is discussed.

Animals↗
PubMed2003

Nitric oxide release from the S-nitrosothiol zinc phthalocyanine complex by flash photolysis.

The photogeneration of nitric oxide (NO) using laser flash photolysis was investigated for S-nitroso-glutathione (GSNO) and S-nitroso-N-acetylcysteine (NacySNO) at pH 6.4 (PBS/HCl) and 7.4 (PBS). Irradiation of S-nitrosothiol with light (lambda = 355 nm followed by absorption spectroscopy) resulted in the homolytic decomposition of NacySNO and GSNO to generate radicals (GS and NacyS ) and NO. The release of NO from donor compounds measured with an ISO-Nometer apparatus was larger at pH 7.4 than pH 6.4. NacySNO was also incorporated into dipalmitoyl-phosphatidylcholine liposomes in the presence and absence of zinc phthalocyanine (ZnPC), a well-known photosensitizer useful for photodynamic therapy. Liposomes are usually used as carriers for hydrophobic compounds such as ZnPC. Inclusion of ZnPC resulted in a decrease in NO liberation in liposomal medium. However, there was a synergistic action of both photosensitizers and S-nitrosothiols resulting in the formation of other reactive species such as peroxynitrite, which is a potent oxidizing agent. These data show that NO release depends on pH and the medium, as well as on the laser energy applied to the system. Changes in the absorption spectrum were monitored as a function of light exposure.

Acetylcysteine↗
PubMed1988

Cone activation delaying recovery time of rod sensitivity after flash exposure.

The recovery time of rods to the fully dark adapted state after flash exposure was psychophysically and electrophysiologically measured. The recovery time increased abruptly once cones were activated. This abrupt increment was not found for the receptor component (P III) of the frog electroretinogram. It was suggested that the cone activation results in inhibitory influence upon the recovery process of the rod sensitivity.

Amplifiers, Electronic↗
PubMed1989

An analysis of several variables influencing the efficacy of flash card instruction.

We conducted four experiments using an alternating treatments design to assess the influence of several variables on children's acquisition of number facts during one-on-one flash card instruction. In Experiment 1, we manipulated the order of stimulus presentation; in most cases a higher percentage of correct responses occurred, and mastery criterion was reached in somewhat fewer sessions, when a missed problem was re-presented after the next item than when problems were re-presented in a sequential order. In Experiment 2 a comparison of error-contingent reprimands with no reprimands yielded similar results in favor of the former procedure. Experiment 3 indicated that a higher percentage of correct responses and more rapid acquisition occurred when the tutor and student were seated knee-to-knee than when a desk was positioned between them. Experiment 4 compared the rate of learning in the presence and absence of a treatment package consisting of all three variables identified as leading to more rapid learning in the previous three experiments. Children reached criterion in less than half the time when the treatment package was in effect.

Journal Article↗
PubMed2006

FlAsH-based live-cell fluorescent imaging of synthetic peptides expressed in Arabidopsis and tobacco.

Genes encoding synthetic hydroxyproline-rich peptides with repetitive (Ser-Pro) units linked to an extensin signal sequence and a tetracysteine (TC) sequence were expressed transiently in tobacco, and transiently and stably in Arabidopsis under control of a strong constitutive promoter Expression of these peptides could be visualized in live cells by confocal microscopy following labeling with FlAsH- or ReAsH-EDT2 reagents.

Arabidopsis↗
PubMed1997

The cross-bridge mechanism studied by flash photolysis of caged ATP in skeletal muscle fibers.

Flash photolysis of caged ATP was first employed in muscle cell physiology about 15 years ago. This technique enables examination of the millisecond dynamics of synchronized cross-bridge ATPases in muscle fibers, and consequently, many photolysis studies have been performed in attempt to elucidate the cross-bridge mechanism. The results of early studies with caged ATP seemed to support the classical "power stroke" theory. However, much of the recent evidence indicates that the contraction induced by the photolysis of caged ATP differs from that predicted by the classical theory. One elusive problem is the biphasic tension development that occurs on the photorelease of ATP in the ADP-rigor fiber in the presence of Ca2+. Another is the long-lasting burst of Pi release after the release of ATP. Further investigations are required to clarify the chemo-morpho-mechanical coupling involved in the cross-bridge reaction.

Actins↗
PubMed1994

Dissection of the thoracic aorta: pre- and postoperative findings on turbo-FLASH MR images obtained in the plane of the aortic arch.

This pictorial essay illustrates the pre- and postoperative findings seen in patients with aortic dissections on contrast-enhanced turbo-fast low-angle shot (FLASH) MR images obtained in the plane of the aortic arch. Contrast-enhanced images provide morphologic and functional information not normally available with conventional spin-echo (SE) MR imaging or dynamic CT. Preoperative examination of the acute dissection is often troubled by cardiovascular insufficiency and motion artifacts. Therefore most of our patients were examined postoperatively. The main reason for postsurgical imaging is the evaluation of the flow in the different lumina and the detection of complications (i.e., aneurysms or progress of dissection).

Aortic Dissection↗
PubMedDate not supplied

["Flash" pulmonary edema as a clinical manifestation of renovascular hypertension].

One of the clinical manifestations of renovascular hypertension (RVH) may be a recurrent pulmonary oedema both in the absence or in the presence of systolic left ventricular dysfunction. This type of pulmonary oedema characterized as "flash" pulmonary oedema is ascribed to elevated angiotensin II concentrations with consequent hypertension as well as to volume overload resulting from decreased pressor natriuresis when there are significant stenoses of both or one renal arteries. The investigation included 30 patients with RVH treated by percutaneous transluminal angioplasty of the stenosed renal artery (PTRA) and/or stent implantation (PTR-ST) and 30 patients with surgical resection of the abdominal aortic aneurysm (AAA). The first group was divided in two subgroups according to the etiology of renal artery stenosis (RAS). In the subgroup with fibromuscular dysplasia (FMD) the mean age was 37.5 years, in the subgroup with atherosclerotic renal artery stenosis (ARAS) 54.8 years and in the group with operated AAA 68.6 years. There were more females than males only in the FMD subgroup (10:3). Two patients of the first group experienced pulmonary oedema, both in the subgroup with atherosclerotic renal artery stenosis associated with atherosclerosis of other arteries. Normalization of the blood pressure following PTRA in both and an uncomplicated course after a surgical myocardial revascularization in one of them illustrates the importance of renal revascularization. Pulmonary oedema occurred preoperatively in four out of 30 patients with abdominal aortic aneurysm in whom significant renal artery stenoses coexisted. Two patients died despite surgery, one patient is clinically stable and the medicament treatment of heart failure is inevitable in the fourth with a left ventricular aneurysm following myocardial infarction. The occurrence or recurrence of pulmonary oedema in the absence of other explanation should suggest the possibility of bilateral or unilateral renal artery stenosis requiring renal revascularization for blood pressure regulation as well as for elimination of other manifestations/complications.

Adult↗
PubMed2000

Evaluation of short-term increased intraocular pressure on flash- and pattern-generated electroretinograms of dogs.

OBJECTIVE: To determine the electrodiagnostic and histologic response of short-term increases of intraocular pressure (IOP) on transient pattern electroretinograms (PERG) and flash electroretinograms (FERG) in the eyes of dogs. ANIMALS: 8 healthy mixed-breed dogs. PROCEDURE: Transient PERG and FERG waveforms were recorded from dogs (while anesthetized) as IOP was increased from baseline (7 to 19 mm Hg) to 90 mm Hg. One hundred mean PERG responses and a single FERG response were recorded at each step during 3 recording sessions. Globes of each dog were enucleated after euthanasia on posttreatment day 7 and evaluated by a pathologist. RESULTS: Increases in spatial frequency resulted in decreased amplitudes of N2 (second negative PERG peak). Increases in IOP resulted in decreases in all 3 PERG waveforms and the FERG waveform. All values began to return to baseline after short-term increases in IOP on day 0, and waveforms were not significantly different on posttreatment days 3 and 7 CONCLUSIONS: Data suggest that short-term increases in IOP affect PERG and FERG waveforms, and PERG waveforms are more sensitive to increases in IOP Differences were not detected between treated and control eyes on histologic examination. Further studies are necessary to determine at what IOP permanent damage to ganglion and photoreceptor cells will develop and whether PERG is a reliable clinical diagnostic technique for use in dogs to reveal retinal damage that is secondary to increased IOP prior to changes in waveforms generated by FERG in dogs.

Animals↗
PubMed1982

Potential changes and eyelid microvibration elicited by flash stimulation.

The photopalpebral reflex evoked in the upper eyelid of the rabbit by flash stimulation was studied in terms of potential change (PPR) and microvibration (MV) and the following conclusions drawn. (1) Of the PPR components, the early components from PPR1 to PPR4 are mainly ERG components, while PPR5 to PPR9 and MV are components appearing via the central nervous system. (2) Excitation of the brainstem reticular formation is involved in the appearance of the central PPR components and MV. Components PPR6 to PPR8 and MV originate in excitation of the same nervous tissue, but PPR9 occurs by excitation of different nervous tissue. (3) Contraction of the extraocular muscles, as well as the orbicularis oculi muscles, is involved in the appearance of MV. (4) Unit discharge takes place in the brainstem reticular formation coinciding with the occurrence of MV and an increase in discharge takes place later. The relation of the increase in this late discharge to PPR9 must be further investigated.

Animals↗