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At least 469 records · Page 26Linked to original sources
PubMed1992

Expression of myosin heavy and light chains and phosphorylation of the phosphorylatable myosin light chain in the heart ventricle of the European hamster during hibernation and in summer.

We investigated the expression of myosin subunits (myosin heavy chains) as well as light chains and the in vivo phosphorylation of the phosphorylatable myosin light chain in the heart ventricle of the adult male European hamster (Cricetus cricetus L.). Two myosin heavy chain isoenzymes could be detected under native and denaturing electrophoretic conditions having high (alpha-myosin heavy chain) and low (beta-myosin heavy chain) enzymatic activity. Enzymatic activity of alpha- and beta-myosin heavy chain revealed a different temperature dependency. When temperature increased ATPase activity of the alpha-myosin heavy chain isoenzyme increased relatively more than ATPase activity of the beta-myosin heavy chain isoenzyme. Summer animals expressed predominantly the beta-myosin heavy chain (79% of total myosin) while during hibernation the alpha-myosin heavy chain expression increased to 53% of total myosin. Winter-active hamsters kept at 22 degrees C and 12 h day/night rhythm showed the same myosin heavy chain isoenzyme pattern as summer-active animals. Two myosin light chain forms were expressed in the ventricle of all animal groups. The in vivo phosphorylation level of the phosphorylatable myosin light chain decreased from 45% in summer-active hamster to 23% during hibernation.

Animals↗
PubMed2006

Orientation by polarized light in the crayfish dorsal light reflex: behavioral and neurophysiological studies.

In decapod crustaceans, the dorsal light reflex rotates the eyestalk so that the dorsal retina faces the brightest segment of dorsal visual space. Stepwise displacements of white stripes elicit eyestalk rotations in the same direction as that of the stripe. Conversely, stepwise displacements of black stripes on a white background elicit eyestalk rotations in the opposite direction as that of the stripe. The reversal of the response with contrast inversion distinguishes the dorsal light reflex from an optokinetic reflex. When the visual scene is composed of polarized light, segmented by variations in e-vector orientation, displacement of segments containing near vertical e-vectors elicit responses similar to those elicited by a white stripe. Displacement of polarized stripes containing near horizontal e-vectors elicit eyestalk rotations similar to those elicited by a black stripe. The results are consistent with the use of polarized light in orientation. The stimulus conditions described above were also applied to visual interneurons (sustaining fibers) and oculomotor neurons and the results were generally in accord with the behavior. In the neural studies, it was possible to show that responses to polarized stripe displacements are predictable from the receptive field location and the neuron's polarization tuning function.

Action Potentials↗
PubMed1985

Light-induced activation of the rod phosphodiesterase leads to a rapid transient increase of near-infrared light scattering.

The so-called AT-signal described here is a transient light-induced increase of the near-infrared scattering from isolated bovine rod outer segments (ROS). Freshly prepared ROS are permeabilized with 0.01% Triton X-100 immediately before measurement in the presence of 1 mM GTP. The signal amplitude is saturated when approximately 2 rhodopsin molecules out of 30 000 are photo-excited. The signal recovers rapidly (approximately 90 s) and can be repeated in a succession of flashes. The AT-signal can be prevented by pre-activation of the phosphodiesterase (PDE) enzyme cascade at various levels: either at the level of G-protein, using ALF4- in darkness or GTP gamma S plus light; or at the level of the PDE catalytic unit, using protamine as an activator. The light sensitivity and kinetics of the AT-signal are similar to published parameters of PDE activation. These data suggest that light-induced activation of the PDE is the key reaction for the generation of the signal. On the other hand, blocking of the catalytic cGMP binding site by isobutylmethylxanthine only slightly affects the signal. We propose that the AT-signal reflects a structural change linked to the transient removal of the PDE inhibitory subunit from the catalytic unit.

1-Methyl-3-isobutylxanthine↗
PubMed1989

Immunoglobulin light chain patterns in the cerebrospinal fluid. A study with special reference to the occurrence of free light chains in cerebrospinal fluid with and without oligoclonal immunoglobulin G.

The immunoglobulin light chain patterns were studied in paired cerebrospinal fluid (CSF) and serum samples from 30 controls, 70 multiple sclerosis (MS) patients, 18 subjects with other inflammatory neurological diseases and 17 patients with other non-inflammatory neurological disorders. In MS, all CSF samples examined by two-dimensional gel electrophoresis exhibited clonally restricted light chain components. Isoelectric focusing and immunoblotting detected free light chains in around 90% of CSF samples from patients with MS or other inflammatory diseases. These components were clonally restricted, appeared in both mono- and dimeric forms and occurred in CSF samples with as well as without oligoclonal immunoglobulin G bands. Generally, the positive CSF samples contained kappa as well as lambda free lights chains. Such components were not detected in the sera, nor in the CSF samples from controls or patients with non-inflammatory diseases.

Brain Diseases↗
PubMed1986

Correlations of serotonin and its metabolites in individual rat pineal glands over light:dark cycles and after acute light exposure.

Profiles of pineal indolealkylamines were estimated by high performance liquid chromatography and were correlated in individual glands of male rats sacrificed over several light:dark cycles and after acute exposure to light at night. A significant and positive correlation of 5HIAA vs 5HT in individual glands over both normal and experimental lighting conditions suggested that oxidative deamination is not a major factor in photic regulation of pineal 5HT levels and that the formation of 5HIAA is dependent on substrate availability. Regression analysis of other indole constituents revealed that there was a positive and significant correlation between 5HT vs N-acetylserotonin, but not between 5HT vs melatonin and N-acetylserotonin vs melatonin in individual glands during the dark phase of a light:dark cycle. We propose that this effect may be related to a pulsatile release of melatonin into the blood stream and is the result of sampling glands at different stages in the storage/release of melatonin.

Animals↗
PubMed1976

Analaysis of photoenzymatic repair of UV lesions in DNA by single light flashes. XI. Light-induced activation of the yeast photoreactivating enzyme.

Photoreactivating enzyme (PRE) from yeast (as semi-crude extract, or in highly purified form) shows increased activity if it is illuminated with near UV or short wavelength visible light prior to its use for photoenzymatic repair of UV-induced pyrimidine dimers in transforming DNA in vitro. This effect results from an alternation in PRE molecules changing those with low activity in the light-dependent step of the reaction to a higher activity. Light-induced activation of PRE preparations is slowly lost by dark storage for several hours to 1 day (faster at 23 degrees C than at 5 degrees C), but can be recovered repeatedly by renewed preillumination. The action spectrum for these preillumination effects generally resembles that for the photoenzymatic repair reaction itself, having its maximum in the same 355-385 nm region as the latter, but light of somewhat longer wavelengths (546 nm) is still effective. Preilluminated PRE is also more stable to thermal inactivation (65 degrees C) than untreated enzyme.

DNA Repair↗
PubMed1993

Effects of scheduled food and water access on circadian rhythms of hamsters in constant light, dark, and light:dark.

Wheel-running activity of 31 Syrian hamsters was monitored in constant light (LL), dark (DD), and light-dark (LD) under ad lib and restricted food and water access schedules. Free-running or damped circadian wheel-running rhythms of 26 hamsters in LL were entrained by exposure to the restriction schedule. The phase of entrainment was positive, i.e., wheel running anticipated access time. In LD, activity was nocturnal. When food and water were restricted to midlight, five hamsters showed additional activity in anticipation of access time. Thirty hamsters showed a small advance of the phase of nocturnal activity onset. In subsequent DD, anticipatory activity was revealed (unmasked) in several additional cases, and nocturnal activity shifted and entrained to the access schedule in 19 cases. The properties of food anticipation and entrainment under the three lighting conditions support a model of the hamster circadian system that incorporates separate but strongly coupled food/water- and light-entrainable pacemakers.

Animals↗
PubMed2006

"Let There be Light!" pigeon eggs are regularly exposed to light during breeding.

Light stimulation before hatching initiates the emergence of avian visual lateralisation. Since several studies show that birds benefit from being lateralised, we can conjecture that their clutch is being exposed to light during breeding. We tested this assumption in pigeons with a semi-natural setup where the animals were systematically recorded using a movement detection system throughout their breeding period. The results show that pigeon pairs perform their relieves in a regular way by abandoning their clutch for a mean of about 55 s at approximately every 43 min. Thus, the developing visual pathways are repetitively stimulated by light for cumulatively over 3h before the breeding period ends. It becomes apparent that both the duration as well as the repetitions of light stimulation play a crucial role in the onset of visual asymmetry.

Animals↗
PubMed2006

Changes in melatonin binding sites under artificial light-dark, constant light and constant dark conditions in the masu salmon brain.

To test whether the affinity (Kd) and total binding capacity (Bmax) of melatonin receptors exhibit daily and circadian changes in teleost fish whose melatonin secretion is not regulated by intra-pineal clocks, we examined the changes in melatonin binding sites in the brains of underyearling masu salmon Oncorhynchus masou under artificial light-dark (LD), constant light (LL) and constant dark (DD) conditions. In Experiment 1, fish were reared under a long (LD 16:8) or short (LD 8:16) photoperiod for 69 days. Blood and brains were sampled eight times at 3 h intervals. Plasma melatonin levels were high during the dark phase and low during the light phase in both photoperiodic groups. The Bmax exhibited no daily variations. Although the Kd slightly, but significantly, changed under LD 8:16, this may be of little physiological significance. In Experiment 2, fish reared under LD 12:12 for 27 days were exposed to LL or DD from the onset of the dark phase under LD 12:12. Blood and brains were sampled 13 times at 4 h intervals for two complete 24 h cycles. Plasma melatonin levels were constantly high in the DD group and low in the LL group. No significant differences were observed in the Kd and the Bmax between the two groups, and the Kd and the Bmax exhibited no circadian variation either in the LL or DD groups. These results indicate that light conditions have little effect on melatonin binding sites in the masu salmon brain.

Animals↗
PubMed2004

Early versus late bedtimes phase shift the human dim light melatonin rhythm despite a fixed morning lights on time.

Short sleep/dark durations are common in modern society. In a within subjects counterbalanced design, we compared the effect of 7-19 nights with a late bedtime (01:00) versus 7-19 nights with an early bedtime (22:00) on the human dim light melatonin rhythm. All ten healthy subjects experienced lights on time at 07:00 and at least 5 min of outdoor light between 07:00 and 08:00. We found that despite the morning light exposure, the melatonin rhythm following the late bedtime nights was delayed by approximately 0.6 h (P<0.05), as compared to after the early bedtime nights. These results suggest that when people truncate their sleep by delaying their bedtime they also significantly phase delay their circadian rhythms and/or when people advance their bedtime their circadian rhythms advance.

Adult↗
PubMed1988

Light-induced phosphoinositide degradation and light-induced structural alterations in the rat retina are enhanced after chronic lithium treatment.

In the rat retina, light-induced break down of polyphosphoinositides and structural alterations of photoreceptor outer segment disk-membranes were enhanced by chronic lithium treatment at doses equivalent to therapeutic levels in humans. Furthermore, the recovery of phosphoinositide baseline levels after light exposure was delayed in lithium treated retinas. Light and lithium may thus affect phospholipid membranes in the retina. Initial processes in the pathogenesis of light damage in the retina are largely unknown to date. The hydrolysis of polyphosphoinositides may possibly constitute such an initial event.

Animals↗
PubMed2004

Performance of two blue light-emitting-diode dental light curing units with distance and irradiation-time.

OBJECTIVES: To assess the performance of two blue light-emitting-diode (LED) curing units, in terms of their spectral output and irradiance and the depth of cure (dcure) produced in standard hybrid and modified composites, compared with a conventional quartz tungsten halogen (QTH) light curing unit. METHODS: The following light curing units (LCUs) were studied: Elipar-Freelight-1 LED (LED-1) 3 M-ESPE, Ultralume-2 LED (LED-2) Optident, and the Optilux-500 QTH (QTH-1) Sybron-Kerr. For each LCU, using a UV-visible spectrophotometer, the output spectrum was measured and the irradiance of emitted light as a function of source-detector distance. Three composites were studied of similar formulation but differing in their initiator concentrations and/or opacity. These were: Tetric Ceram (A3), Tetric Ceram HB containing an additional photoinitiator responding to approximately 435 nm (A3) and Tetric Ceram Bleach (L). dcure was measured using a calibrated digital needle-penetrometer, as a function of source-specimen distance and for irradiance periods of 10, 20 and 40 s. RESULTS: Each unit delivered a single peak in the blue region of the visible spectrum. The wavelength maxima for LED-1, LED-2 and QTH-1 were 486.4, 458.2 and 495.2 nm, respectively. Cure-depth (dcure) values varied significantly (p<0.001) with irradiance times and source-specimen distance for both LED and QTH sources. The percentage reduction in dcure values resulting from LED versus QTH irradiance increased with source-specimen distance. SIGNIFICANCE: The LED-LCUs had an energy-efficient spectral output for conventional composite curing but had a lower irradiance compared with the QTH-LCU, leading to reduced performance in depths of cure. Design improvements to provide greater irradiance from the LED-1 and to a lesser extent LED-2, should result in increased performance.

Analysis of Variance↗
PubMed2002

High power light emitting diode (LED) arrays versus halogen light polymerization of oral biomaterials: Barcol hardness, compressive strength and radiometric properties.

The clinical performance of light polymerized dental composites is greatly influenced by the quality of the light curing unit (LCU) used. Commonly used halogen LCUs have some specific drawbacks such as decreasing light output with time. This may result in a low degree of monomer conversion of the composites with negative clinical implications. Previous studies have shown that blue light emitting diode (LED) LCUs have the potential to polymerize dental composites without having the drawbacks of halogen LCUs. Since these studies were carried out LED technology has advanced significantly and commercial LED LCUs are now becoming available. This study investigates the Barcol hardness as a function of depth, and the compressive strength of dental composites that had been polymerized for 40 or 20s with two high power LED LCU prototypes, a commercial LED LCU, and a commercial halogen LCU. In addition the radiometric properties of the LCUs were characterized. The two high power prototype LED LCUs and the halogen LCU showed a satisfactory and similar hardness-depth performance whereas the hardness of the materials polymerized with the commercial LED LCU rapidly decreased with sample depth and reduced polymerization time (20 s). There were statistically significant differences in the overall compressive strengths of composites polymerized with different LCUs at the 95% significance level (p = 0.0016) with the two high power LED LCU prototypes and the halogen LCU forming a statistically homogenous group. In conclusion, LED LCU polymerization technology can reach the performance level of halogen LCUs. One of the first commercial LED LCUs however lacked the power reserves of the high power LED LCU prototypes.

Biocompatible Materials↗
PubMed2001

A novel airlift photobioreactor with baffles for improved light utilization through the flashing light effect.

A newly developed flat panel airlift photobioreactor with a defined circulation path was tested for microalgal culture. The bioreactor exposed the cells to intermittent light to improve the efficiency of light utilization through the flashing-light effect. During batch cultures in the new photobioreactor, the biomass productivity of Chlorella vulgaris was 1.7 times greater than in a randomly mixed bubble column of identical dimension. A reduction in light path from 30 to 15 mm increased the biomass productivity by 2.5-fold. A maximum dry biomass productivity of 0.11 g l(-1) h(-1) was obtained at an artificial illumination of 980 mu E m(-2) s(-1).

Biomass↗
PubMed2002

Light-regulated subcellular translocation of Drosophila TRPL channels induces long-term adaptation and modifies the light-induced current.

Drosophila phototransduction results in the opening of two classes of cation channels, composed of the channel subunits transient receptor potential (TRP), TRP-like (TRPL), and TRPgamma. Here, we report that one of these subunits, TRPL, is translocated back and forth between the signaling membrane and an intracellular compartment by a light-regulated mechanism. A high level of rhabdomeral TRPL, characteristic of dark-raised flies, is functionally manifested in the properties of the light-induced current. These flies are more sensitive than flies with no or reduced TRPL level to dim background lights, and they respond to a wider range of light intensities, which fit them to function better in darkness or dim background illumination. Thus, TRPL translocation represents a novel mechanism to fine tune visual responses.

Adaptation, Ocular↗
PubMed1997

Inhibition of pteridine biosynthesis eliminates blue-light dependent stimulation of red-light saturated photosynthesis in Laminaria saccharina (L.) Lamouroux.

Blue-light stimulation of red light-saturated photosynthetic oxygen evolution in Laminaria saccharina (L.) Lamouroux could be abolished within 5 days by incubation in a solution of 2,4-diamino-6-hydroxypyrimidine (DAHP), an inhibitor of GTP-cyclohydrolase I (E.C.3.5.4.16) activity. Photosynthesis in red light was not detectably affected. GTP-cyclohydrolase I, which catalyses the first step in the biosynthetic pathway of pteridines, was shown to be active in Laminaria. Under conditions that lead to complete inhibition of the photosynthetic stimulation, DAHP reduced the content of the pteridines in the tissue considerably. The amount of pterin was about 14%, that of biopterin was about 45% and that of an unidentified pteridine was about 27% of those of the controls. By contrast, the total concentration of flavins (FAD + FMN - riboflavin) was not significantly affected. The results suggest that pterins may be involved in the response of photosynthesis to blue light, possibly participating in photoreception.

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

The determination of total cGMP levels in rod outer segments from intact toad photoreceptors in response to light superimposed on background and to consecutive flashes: a second light flash accelerates the dark recovery rate of cGMP levels in control media, but not in Na(+)-free, low Ca2+ medium.

In previous experiments we established that a light flash reduced cGMP levels of toad rod outer segments within the transduction time interval, but that recovery of the dark level of cGMP occurred more slowly than reported electrophysiological recovery of membrane potential. We now report that a second light flash accelerates the recovery rate of total cGMP following an initial flash, but that this acceleration is blocked in a medium which is both sodium and calcium deficient. We also noted that calcium deficiency only elevated cGMP levels when sodium was present. For other experiments, we recorded ERG or aspartate isolated PIII responses from eyecups or retinas mounted on our quick-freeze apparatus, the light stimuli originating from the double light-bench of the latter. Whereas background illumination depressed cGMP, no detectable further cGMP loss accompanied the electrical response to a flash superimposed on the background.

Animals↗
PubMedDate not supplied

Induction of retinal degeneration in a crab by light and okadaic acid in vitro: comparison with the Drosophila light-dependent retinal degeneration mutant w rdgBKS222.

Retinae of the crab Leptograpsus which had been maintained on a 12-h light/12-h dark cycle were cultured in vitro and exposed to 1 microM okadaic acid (OKA) at 0.75 h before light onset. Control retinae were subjected to the same routine and sampled at the same times without OKA treatment. At the concentration used, OKA totally inhibits types 1 and 2A protein phosphatases, minimally inhibits type 2B, and does not affect type 2C. 1 microM OKA provoked a diminution of rhabdom diameter measured at the level of the photoreceptor nuclei in the dark, some ommatidial cartridges being stripped of rhabdomeral microvilli altogether. After 1-h illumination (225-320 lux), further reduction of rhabdom diameter was modest in control retinae but precipitate in those treated with OKA. After 2 h, control rhabdom diameters showed a further, not significant, decline, but OKA had induced a resynthesis of massive structures with the light-microscopic appearance of rhabdoms. Electron microscopy revealed that they were heterogeneous and of the following kinds: (1) a minority of rhabdoms with normally disposed but distorted microvilli; (2) rhabdoms in the throes of events that parody normal assembly; and (3) rhabdomal volumes occupied by saccular organelles or by pleats or ruffles of irregular architecture. The cytoplasm of all such receptors was packed with free and bound ribosomes and endomembranes. The sequence of events parallels that seen during light-induced degeneration of photoreceptors of the Drosophila mutant w rdgBKS222. Preliminary experiments show that a protein kinase activator SC-9 mimics many of these effects in the dark in the presence of 1 microM OKA. As a working hypothesis, it is proposed that light activates protein kinases via diacylglycerols generated by the phototransduction cascade, and that in both crab retinas challenged with OKA and retinas of rdg BKS222 activation of a nuclear regulatory protein by hyperphosphorylation provokes a runaway transcription whose selectivity and extent remain to be determined.

Animals↗