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PubMed1987

Normative data and control studies of flash VEP's for comparison to a clinical population.

The effects of aging, interocular comparisons, pupil dilation, iris pigmentation, and simulated cataracts on bright flash visual evoked potentials (VEP's) of normal observers were studied to assess the flash VEP as a potential predictor of postsurgical visual function in cataract patients. Seventy-six observers (from 20 to 80 years old) were tested for age differences in flash VEP's. Implicit time measures for transient responses increased significantly as a function of age, but neither transient nor steady-state response amplitudes were altered significantly. Moreover, no significant changes in VEP's occurred as a function of interocular comparisons, pupil dilation, or differences in iris pigmentation of normal observers. Simulation of cataracts with 14 observers did not affect implicit time measures, but did change response amplitudes significantly. Therefore, implicit time measures of cataract patients should be compared either to those of normal age-matched controls or, in the case of a unilateral problem, to the normal fellow eye. Delayed implicit time measures, after the appropriate comparison, suggest optic nerve/pathway dysfunction. However, comparisons of amplitude measures require compensation for opacity density.

Adult↗
PubMed1995

Flash visual evoked potential (VEP) in amblyopia and optic nerve disease.

Amblyopia and optic atrophy are two very different causes of unilateral long-standing visual impairment. Yet, in some patients the differential diagnosis is not always manifest and standard clinical tests may fail to provide accurate information. We tested the efficacy of a nonstandard clinical test [flash visual evoked potentials (VEP's)] and quantitative multivariate statistical techniques as aids in the assessment of this differential. Thirty-three patients were separated into four groups (normal, anisometropic amblyopia, strabismic amblyopia, and unilateral optic atrophy). Non-patterned flash VEP's were obtained using several different temporal frequency rates. Patients with optic atrophy had significantly reduced VEP's in the affected eye at all temporal frequencies. Strabismic amblyopes, but not anisometropic amblyopes, often showed supranormal responses in the affected eye at the higher temporal frequencies. Finally, by using discriminant analysis (DA) we were able to classify correctly almost 70% of the patients, well above chance level of 25%. This DA provided very good sensitivity and specificity. We have shown that the use of flash VEP's and of multivariate statistical techniques may provide an effective way to diagnose amblyopia differentially from optic atrophy.

Amblyopia↗
PubMedDate not supplied

Evaluation of closed container flash sterilization system.

Flash sterilization is a rapid, effective procedure for providing sterile instruments for surgery; however, aseptic transport of an unwrapped sterile tray is a major problem. This study tested the effectiveness of using a closed container for flash sterilization, and found the closed container to be an effective alternative to the traditional open tray for flash sterilization and transportation of sterile supplies.

Evaluation Studies as Topic↗
PubMed1996

Positive chronotropic responses of rabbit sino-atrial node cells to flash photolysis of caged isoproterenol and cyclic AMP.

The kinetics of onset and the intracellular biochemical signalling mechanisms which are responsible for the positive chronotropic effect of sympathetic stimulation in rabbit cardiac pacemaker cells were examined by using flash photolysis of caged isoproterenol (ISO) and cyclic AMP (cAMP). When caged ISO (10 microM) was present in the superfusate, a single ultraviolet flash caused gradual increases in the spontaneous beating frequency and action potential height of S-A node cells. Both these effects developed after an initial latency of approximately 5 s. Photorelease of ISO also increased the L-type Ca2+ current (ICa-L) with a time-course similar to that of the changes in action potential waveform and heart rate. All of these ISO-induced effects were blocked completely by 1 microM propranolol, demonstrating that they were beta-adrenergic responses. Flash photolysis of caged cAMP (50 microM) also resulted in increased firing frequency and ICa-L. However, these responses to cAMP developed with little or no latency. Intracellular dialysis with a selective inhibitor of the cAMP-dependent protein kinase, Rp-cAMPS, completely abolished the increase in ICa-L demonstrating that it is mediated exclusively via cAMP-dependent activation of protein kinase A, as opposed to a direct G-protein mediated mechanism.

Action Potentials↗
PubMed1976

Correlation of absorbance changes and thylakoid fusion with the induction of oxygen evolution in bean leaves greened by brief flashes.

Dark-grown bean leaves (Phaseolus vulgaris) which had been greened for several days in a repetitive series of brief xenon flashes were studied during the initial induction period when O(2) evolution first appears. The induction of O(2) evolution requires actinic irradiation (e.g. 2 mw/cm(2) of red light) and goes to completion in about 8 minutes with a half-time just under 3 minutes. Absorbance measurements on the intact leaves showed that a change of a carotenoid pigment, monitored at 505 nm, was closely correlated with the rate of O(2) evolution during the induction period. Inhibitor studies, however, showed that the absorbance change persisted in the presence of a number of inhibitors which blocked O(2) evolution. Electron microscopy revealed that the primary thylakoids which were unfused in the flashed leaves before induction became fused in pairs or groups of three during the 8-minute induction period. It is postulated that the 505-nm absorbance change of the carotenoid pigment is correlated more directly with the fusion process than with O(2) evolution. Heat treatment (45 C for 5 min) or infiltration with 0.8 m tris, which prevented the fusion process, also prevented the absorbance change.If the leaves were preilluminated for 8 minutes with very weak red light (20 muw/cm(2)) which induced no O(2) evolution, absorbance change, or thylakoid fusion, there was an immediate burst of O(2) evolution at the onset of actinic irradiation and the induction period, as noted by O(2) evolution or by the 505-nm absorbance change, was reduced to 2 minutes (half-time of 40 seconds). It is concluded that the electron transport system in the flashed leaves is blocked at the Mn site between water and photosystem II and that the photoactivation of Mn into the thylakoid membranes occurs during the low light, photoactivation process. After the electron transport chain is thus repaired, ion-pumping mechanisms driven by actinic light may lead to steady-state photosynthesis as well as to thylakoid fusion.

Journal Article↗
PubMed1979

Characteristics of the Flash-induced 515 Nanometer Absorbance Change of Intact Isolated Chloroplasts.

In intact (type A) chloroplasts isolated from mesophyll protoplasts of maize (Zea mays L. convar. KSC 360) the flash-induced 515 nanometer absorbance change was much higher than in conventionally prepared (types B and C) chloroplasts. The 515 nanometer signal of type A chloroplasts exhibited a biphasic rise: the initial very fast rise (rise time <<1 millisecond) was followed by a slow increase of absorbance (rise time 10 to 20 milliseconds). With decreasing degree of envelope retention the slow phase disappeared. Thus the biphasic rise of the flash-induced 515 nanometer absorbance change can be regarded as an attribute of intact chloroplasts.The 515 nanometer signal of intact chloroplasts was studied at various pH values of the external medium, with various dark intervals between the flashes and at different temperatures. The absorbance change was probed with electron transport inhibitors and ionophores. The data show that the fast phase of the absorbance increase was similar in chloroplasts isolated from protoplasts and in conventional chloroplast preparations. The slow rise, which has not been hitherto recognized in isolated chloroplasts, can be due to a contribution of the proton pump to the electric field which is generated across the thylakoid membranes.

Journal Article↗
PubMed1987

Effects of the Timing of Flashes of Light during the Course of Cellular Rotation on Phototactic Orientation of Individual Cells of Cryptomonas.

The swimming movement of Cryptomonas sp. cells generates a helical path, as a result of rotations with an average period of 500 milliseconds. When a flash of light at 570 nanometers for 20 microseconds was applied unidirectionally at intervals of 500 milliseconds, only a fixed side of each rotating cell was repeatedly exposed to the flashes of light. The relationship between the irradiated side of a cell and the phototactic orientation of the cell, rotating with a period of 475 to 525 milliseconds, was determined by infrared videomicrography. Only when the ventral sides of the cells were exposed to the flashes of light did their courses shift predominantly toward the light source. This result suggests that light is efficiently detected by the ventral side of these organisms.

Journal Article↗
PubMed2003

Heat transfer from protein crystals: implications for flash-cooling and X-ray beam heating.

Three problems involving heat transfer from a protein crystal to a cooling agent are analyzed: flash-cooling in a cold nitrogen- or helium-gas stream, plunge-cooling into liquid nitrogen, propane or ethane and crystal heating in a cold gas stream owing to X-ray absorption. Heat transfer occurs by conduction inside the crystal and by convection from the crystal's outer surface to the cooling fluid. For flash-cooling in cold gas streams, heat transfer is limited by the rate of external convection; internal temperature gradients and crystal strains during cooling are very small. Helium gas provides only a threefold improvement in cooling rates relative to nitrogen because its much larger thermal conductivity is offset by its larger kinematic viscosity. Characteristic cooling times vary with crystal size L as L(3/2) and theoretical estimates of these times are consistent with experiments. Plunge-cooling into liquid cryogens, which can give much smaller convective thermal resistances provided that surface boiling is eliminated, can increase cooling rates by more than an order of magnitude. However, the internal conduction resistance is no longer negligible, producing much larger internal temperature gradients and strains that may damage larger crystals. Based on this analysis, factors affecting the success of flash-cooling experiments can be ordered from most to least important as follows: (1) crystal solvent content and solvent composition, (2) crystal size and shape, (3) amount of residual liquid around the crystal, (4) cooling method (liquid plunge versus gas stream), (5) choice of gas/liquid and (6) relative speed between cooling fluid and crystal. Crystal heating by X-ray absorption on present high-flux beamlines should be small. For a fixed flux and illuminated area, heating can be reduced by using crystals with areas normal to the beam that are much larger than the beam area.

Algorithms↗
PubMed2005

The effects of flash-annealing on glycerol kinase crystals.

Reflection profiles from glycerol kinase crystals were analyzed to determine the effect of flash-cooling on mosaicity (eta) and peak intensity in order to reveal changes in mosaic domain structure and composition. The results showed that repeated flash-annealing causes a significant decrease in the averaged mosaicity along with an increase in the overall peak counts of reflections and an enhanced signal-to-noise ratio. Individual reflection-profile analysis revealed a mostly dual domain structure, showing the minimization of one domain as a result of flash-annealing.

Crystallization↗
PubMed2005

Detection of increased local excitatory circuits in the hippocampus during epileptogenesis using focal flash photolysis of caged glutamate.

PURPOSE: Local synaptic circuits, particularly recurrent excitation, are hypothesized to contribute to the generation and synchronization of epileptiform activity. The present study tested whether local excitatory circuits in the hippocampus are increased in an animal model of temporal lobe epilepsy, and thus may contribute to epileptic seizures. METHODS: Rats were given hourly injections of kainic acid to induce status epilepticus, which led to chronic epilepsy with spontaneous recurrent seizures. Whole-cell recording was performed in hippocampal slices, and focal flash photolysis of caged glutamate was used to detect local excitatory circuits. RESULTS: In the dentate gyrus of rats with kainate-induced epilepsy and mossy fiber sprouting, focal stimulations with caged glutamate at many different sites in the granule cell layer consistently evoked repetitive excitatory postsynaptic currents (EPSCs) in normal medium and prolonged bursts of action potentials in bicuculline; these responses were not observed in similarly treated slices from control rats. In CA1, focal flash photolysis of caged glutamate in stratum pyramidale revealed significantly more excitatory connections between CA1 pyramidal cells in rats with kainate-induced epilepsy than saline-treated control animals. CONCLUSION: Focal flash photolysis of caged glutamate revealed that new local excitatory circuits are formed in both the dentate gyrus and CA1 area of rats with kainate-induced epilepsy, which supports the hypothesis that the progressive formation of new local excitatory circuits occurs in many locations during epileptogenesis.

Animals↗
PubMed1989

The stepwise biphotonic photoionization of chlorpromazine as seen by laser flash photolysis.

It is generally accepted that both promazine (PZ) and chlorpromazine (CPZ) photionize monophotonically to their respective cation radicals and the corresponding hydrated electrons. It is also supposed that this photoinization has a role in the phototoxic effects of these drugs. However, using laser flash photolysis, we have observed that photoionization of CPZ during S1 excitation (lambda greater than 300 nm) is a stepwise biphotonic process. In the case of PZ our flash photolysis results are less clearcut, but are consistent with stepwise biphotonic photoionization for S1 excitation. We demonstrate, using computer simulation of the intramolecular kinetics, that the estimated triplet state lifetime of CPZ is sufficiently long (23 ns at room temperature) to account for the apparent monophotonic photoionization that has been observed by others at high light intensities and short pulse times. Our laser flash photolysis results also suggest that the photo-ionization mechanism of PZ and CPZ is wavelength-dependent. Both drugs exhibit apparent monophotonic photoionization when they are excited at 266 nm under conditions of laser pulse width and intensity similar to those at 355 nm. We suggest that photoionization is not an important mechanism in the observed phototoxic and photoallergic effects of PZ and CPZ in sunlight.

Chlorpromazine↗
PubMed1996

Damage to UV-sensitive cells by short UV in photographic flashes.

Light emitted by electronic photographic flash units is shown to damage bacteria and human skin fibroblasts deficient in repair systems, with survival curves very similar to those produced by 254 nm short UV. The lesions induced by these flashes are as photorepairable by the photolyase enzyme as those induced by 254 nm UV and result in equivalent survival rates. Biological dosimetry performed with microorganisms highly sensitive to UV (Escherichia coli K12 AB2480, deficient in excision and recombinational-dependent repair systems and Bacillus subtilis UVSSP spores, deficient in excision and in a specific spore repair process) revealed that each 1 ms flash of light from the photographic unit used in this work contained the equivalent of 0.25 J m-2 of 254 nm UV, when measured at a distance of 7.0 cm. This dose of UV was found to be lethal to both repair-deficient E. coli bacteria and repair-deficient human skin fibroblasts obtained from xeroderma pigmentosum donors, as well as mutagenic in B/r wild-type and HCR-mutant bacteria.

Bacillus subtilis↗
PubMed1969

Flash bleaching of rhodopsin in the human retina.

1. Measurements were made of the photo-sensitivity of rhodopsin in the living human retina following bleaching with (a) a flash less than 1 msec in duration, (b) a continuous exposure lasting 30 sec.2. The apparatus consisted of a fundus reflectometer coupled to a computer for on-line processing. Three subjects were studied.3. The relations between the quantity of pigment bleached and the incident energy are so similar for the flash and continuous exposure tests that the occurrence of photo-reversal (such as has been reported in similar circumstances for visual pigment in solution) seems to be ruled out.4. Nonetheless, the two experimental conditions lead qualitatively to two different photo-chemical states in as much as the density difference spectrum for the flash exposure is displaced toward longer wave-lengths in comparison with the data obtained with the continuous exposure.5. The results are discussed with reference to the sequence of events following the bleaching of visual pigments solutions as reported by other workers.

Fundus Oculi↗
PubMed1969

Factors influencing the time course of S-potentials resulting from brief flashes.

1. Wave forms of the S-potential (luminosity-type) from the tench retina were analysed with single or repetitive flashes.2. In tench the slope of the ;ON' phase was dependent on the relative flash intensity but was independent of flash duration (if it was longer than 15 msec) and the state of adaptation.3. The slope of the ;OFF' phase was a dual function of flash duration and of the state of adaptation. Light adaptation brought forth a sharp ;OFF' phase, referred to as ;cut-off' in this paper.4. Temporal or spatial contrast of light and darkness was necessary for the appearance of the cut-off which was partly responsible for complex wave forms of the L-type potential.5. As far as the wave form is concerned the information on the state of adaptation is well processed before it is fed into the S-space as voltage and does not appear there as a shift in d.c. level.

Adaptation, Ocular↗
PubMed1974

The electrical response of turtle cones to flashes and steps of light.

1. The linear response of turtle cones to weak flashes or steps of light was usually well fitted by equations based on a chain of six or seven reactions with time constants varying over about a 6-fold range.2. The temperature coefficient (Q(10)) of the reciprocal of the time to peak of the response to a flash was 1.8 (15-25 degrees C), corresponding to an activation energy of 10 kcal/mole.3. Electrical measurements with one internal electrode and a balancing circuit gave the following results on red-sensitive cones of high resistance: resistance across cell surface in dark 50-170 MOmega; time constant in dark 4-6.5 msec. The effect of a bright light was to increase the resistance and time constant by 10-30%.4. If the cell time constant, resting potential and maximum hyperpolarization are known, the fraction of ionic channels blocked by light at any instant can be calculated from the hyperpolarization and its rate of change. At times less than 50 msec the shape of this relation is consistent with the idea that the concentration of a blocking molecule which varies linearly with light intensity is in equilibrium with the fraction of ionic channels blocked.5. The rising phase of the response to flashes and steps of light covering a 10(5)-fold range of intensities is well fitted by a theory in which the essential assumptions are that (i) light starts a linear chain of reactions leading to the production of a substance which blocks ionic channels in the outer segment, (ii) an equilibrium between the blocking molecules and unblocked channels is established rapidly, and (iii) the electrical properties of the cell can be represented by a simple circuit with a time constant in the dark of about 6 msec.6. Deviations from the simple theory which occur after 50 msec are attributed partly to a time-dependent desensitization mechanism and partly to a change in saturation potential resulting from a voltage-dependent change in conductance.7. The existence of several components in the relaxation of the potential to its resting level can be explained by supposing that the ;substance' which blocks light sensitive ionic channels is inactivated in a series of steps.

Animals↗
PubMed1974

Reconstruction of the electrical responses of turtle cones to flashes and steps of light.

1. Theoretical equations which predict the electrical response of turtle cones to a wide range of light stimuli are developed from the experiments described in previous papers.2. The central points in the theory are that (a) light starts a chain of reactions leading to the production of a substance which blocks ionic channels in the outer segment, (b) an equilibrium between blocking molecules and open channels is rapidly established, (c) the blocking molecules are removed or inactivated by a chain of reactions, the first of which is autocatalytic, (d) in addition to the conductance which decreases with light there is also a conductance which increases with a delay when the cone is hyperpolarized.3. Parameters in the theory were deduced by approximate equations from the experiments described in the previous papers.4. There was good agreement between the properties of real and model cones in the following cases: (a) the response to 10 msec flashes and 0.7 sec steps of light calculated to give between 20 and 5 x 10(7) photoisomerizations per cone at times extending to about 2 sec; (b) the complicated changes in the response to a test flash that occur when it is superposed on background lights of increasing intensity; (c) the after-hyperpolarization and period of reduced sensitivity following a strong flash.5. The main defect of the theory is that the effect of background light in shortening the time to maximum of the response to a flash was more pronounced in a real cone than in the model.

Animals↗
PubMed1975

Rushton's paradox: rod dark adaptation after flash photolysis.

1. Rod dark adaptations after a photoregenerating flash and quantum-equivalent 30 sec bleach are found to be in exact agreement, while the measured rhodopsin regenerations are grossly different. This finding confirms and clarifies "Rushton's paradox', the failure of the Dowling-Rushton equation (linking log sensitivity linearly with unregenerated rhodopsin) to account for human rod dark adaptation after flash photolysis. 2. The hypothesis that the agreement between rod dark adaptation curves after a photoregenerating flash and after a quantum-equivalent 30 sec bleach is coincidental is rejected on the basic of two classes of experiments. 3. Rod "bleaching' adaptation is demonstrated to be entirely determined by the number of rhodopsin molecules which absorb at least one quantum in a temporal period T, whose range includes the time interval 600 musec less than or equal T less than or equal 30 sec. This generalization obtains over the entire scotopic energy range (congruent to 3 log units) where rod dark adaptations has been studied. 4. Thus, the state of "bleaching' adaptation is determined by some by-product of the normal chain of events in scotopic excitation. About this by-product three important deductions are made: (i) its production is a monotonic function of the initial effective quantum absorptions; (ii) its production occurs before the metarhodopsin I leads to to metarhodopsin II dark reaction; (iii) it cannot be any photoproduct of the rhodopsin cycle.

Dark Adaptation↗
PubMed1995

Activation of Ca(2+)-dependent Cl- currents in cultured rat sensory neurones by flash photolysis of DM-nitrophen.

1. Voltage-gated Ca2+ currents (ICa) and Ca(2+)-activated Cl- currents (ICl(Ca)) were recorded from cultured rat dorsal root ganglion (DRG) neurones using the whole-cell configuration of the patch clamp technique. Intracellular photorelease of Ca2+ by flash photolysis of DM-nitrophen elicited transient inward currents only in those cells which possessed Ca(2+)-activated Cl- tail currents following ICa. The reversal potential of the flash responses was hyperpolarized when extracellular Cl- was replaced by SCN-. The flash responses and the Ca(2+)-activated Cl- tail currents were inhibited by the Cl- channel blockers niflumic acid (10-100 microM) and 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) (10 microM). 2. After activation by ICa, the Ca(2+)-activated Cl- current could be reactivated during its decay by photorelease of caged Ca2+. Experiments carried out on neurones held at 0 mV demonstrated that ICl(Ca) could be chronically activated due to residual Ca2+ influx. These data directly demonstrated that the decay of ICl(Ca) is not due to inactivation but rather to deactivation as a result of removal of the Ca2+ load from the cell cytoplasm. 3. Photorelease of caged inositol 1,4,5-trisphosphate (IP3) failed to activate any Ca(2+)-dependent current responses in cultured DRG neurones, although application of caffeine elicited transient inward currents, and responses to photoreleased IP3 could be obtained from freshly dissociated smooth muscle cells. 4. Photorelease of Ca2+ provides a useful method for investigating the properties of ICl(Ca) independently from other physiological parameters. In addition, we have directly demonstrated that ICl(Ca) in DRG neurones does not inactivate, and so may continue to modulate membrane excitability as long as the intracellular Ca2+ concentration ([Ca2+]i) close to the cell membrane is elevated.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗