Light- and nucleotide-dependent binding of phosphodiesterase to rod disk membranes: correlation with light-scattering changes and vesicle aggregation

Under conditions in which large guanosine cyclic 3',5'-phosphate (cGMP)- and phosphodiesterase (PDE)-dependent changes in near-infrared transmission and vesicle aggregation and disaggregation occur, we have observed a striking change in the binding of PDE to rod disk membranes. The change in PDE binding is nucleotide and light dependent as are the light-scattering changes. The cGMP- and PDE-dependent light-scattering signal can be produced by a 500-nm light flash which bleaches 1/(1 X 10(7] rhodopsin molecules. Mg ions are an essential cofactor for the nucleotide-dependent PDE binding and light-scattering changes. 3-Isobutyl-1-methylxanthine and other competitive inhibitors of PDE hydrolytic activity support increased PDE binding to the disk membrane, vesicle aggregation, and the light-scattering signal. However, treatments which block GTP-dependent activation of PDE hydrolytic activity (colchicine, GDP, or ethylenediaminetetraacetic acid) also block these phenomena. Thus, GTP-dependent activation of PDE rather than its hydrolytic activity appears to be correlated with the light-scattering signal.     

Phorbol 12-myristate 13-acetate modulates the cAMP-induced light-scattering response of a Dictyostelium disco?deum cell population

The effect of phorbol 12-myristate 13-acetate upon the light-scattering response to cAMP of a D. disco?deum cell suspension was investigated. It was found that the first spike of the cAMP-mediated light-scattering change (peaking at about 15-20 s after stimulation) was inhibited by the phorbol ester. This effect was concentration dependent with an half-maximum value for the inhibition of 4 nM. The inhibition was found to be maximal after a 10-20 min incubation time. The phorbol ester was shown to affect the dose-response relationship between the cAMP concentration and the relative amplitude of the light-scattering change, more by decreasing the number of cAMP receptors than by decreasing their apparent affinity for cAMP.     

The influence of photometer design on optical-conformational changes.

When cells and large subcellular structures suffer a change in volume or internal structure, their light-scattering properties are normally altered. These optical-conformation changes are potential sources of information about conformation and processes which alter it. Classical light-scattering theory for spherical particles is used to determine how the transmittance or extinction of a cell suspension should respond when such a conformational change occurs and the measurements are made with a conventional photometer. This extends an earlier study of transmittances measured with an “ideal” photometer. The photocell of an ideal instrument collects only the directly transmitted light. In a conventional instrument it also collects the light scattered at small angles, which is usually most of the scattered light. Extinction (optical density, absorbance) of suspensions of spherical cells was computed for several photometer designs. It is found that γ, the angle of acceptance of the photocell, has a significant influence on the extent and even the nature of the photometric response to a given conformational change. Earlier, it was shown that a decrease in cell volume or increase in internal structure will increase extinction for cells of many sizes. Now it is found that a large γ-value increases these effects. An approach to the interpretation of transmitted light fluxes in terms of theoretical predictions is outlined.     

Photoperiodic Regulation of Photosynthate Partitioning in Leaves of Digitaria decumbens Stent

In leaves of pangolagrass (Digitaria decumbens Stent.), the proportion of photosynthate partitioned into starch adjusts to a change in daylength within 24 hours. After a single 14-hour long day, the relative starch accumulation rate is approximately 50% of that under 7-hour short days. This rapid response was exploited to study the light requirement for the perception of changes in daylength. It was found for short day-grown plants that: (a) 7-hour daylength extensions with dim white light (below the light compensation point for photosynthesis); (b) 7-hour daylength extensions with dim far red light (wavelengths greater than 690 nanomoles); or (c) 0.5-hour night-break irradiations with bright white light were all capable of producing about one-half of the effect of a 7-hour daylength extension with bright light. However, long periods of bright light were not required for a complete effect, since a 7-hour shifted short day (i.e. beginning 7 hours later than usual) was as effective as a 14-hour-long day itself. There was also a critical daylength between 11 and 12 hours for the transition between short-day and long-day partitioning patterns. Photoperiod determination depends, at least in part, on a nonphotosynthetic photoreceptor sensitive to both visible and far red irradiation. The duration of the photosynthetic period, as shown in experiments with low-pressure sodium lamps, does not by itself determine the response to daylength.     

Bright Light Exposure During the Daytime Affects Circadian Rhythms of Urinary Melatonin and Salivary Immunoglobulin A

The effects of bright light exposure during the daytime on circadian urinary melatonin and salivary immunoglobulin A (IgA) rhythms were investigated in an environmental chamber controlled at a global temperature of 27°C ± 0.2°C and a relative humidity of 60% ± 5%. Seven diurnally active healthy females were studied twice, in bright and dim light conditions. Bright light of 5000 lux was provided by placing fluorescent lamps about 1 meter in front of the subjects during the daytime exposure (06:30-19:30) from 06:30 on day 1 to 10:30 on day 3. Dim light was controlled at 200 lux, and the subjects were allowed to sleep from 22:30 to 06:30 under both light exposure conditions. Urine and saliva were collected at 4h intervals for assessing melatonin and IgA. Melatonin excretion in the urine was significantly greater during the nighttime (i.e., at 06:30 on day 1 and at 02:30 on day 2) after the bright light condition than during the dim light condition. Furthermore, the concentration and the amount of salivary IgA tended to be higher in the bright light than in the dim light condition, especially during the nighttime. Also, salivary IgA concentration and the total amount secreted in the saliva were significantly positively correlated with urinary melatonin. These results are consistent with the hypothesis that bright light exposure during the daytime enhances the nocturnal melatonin increase and activates the mucosal immune response.     

Kinetics of allophycocyanin's trimer-monomer equilibrium

Kinetic studies of the dissociation of allophycocyanin trimers to monomers have been performed by using stopped-flow techniques. The dissociation was monitored by two techniques: by light scattering to observe the molecular weight changes directly and by 650-nm absorbance to observe the linkage of quaternary structure to spectra. The light-scattering experiments showed a simple exponential decay of trimers to monomers with a dissociation constant of 0.23 s-1. The absorption changes were complex, with two processes occurring. The faster absorption change appeared to be almost simultaneous with the molecular weight change (about 0.27 s-1) and was perhaps totally coordinated with it. The slower absorption change (0.071 s-1) was possibly a result of a conformational change in the chromophore arising during the conversion from newly dissociated monomers to equilibrium monomers.     

Efficacy of a single sequence of intermittent bright light pulses for delaying circadian phase in humans

It has been shown in animal studies that exposure to brief pulses of bright light can phase shift the circadian pacemaker and that the resetting action of light is most efficient during the first minutes of light exposure. In humans, multiple consecutive days of exposure to brief bright light pulses have been shown to phase shift the circadian pacemaker. The aim of the present study was to determine whether a single sequence of brief bright light pulses administered during the early biological night would phase delay the human circadian pacemaker. Twenty-one healthy young subjects underwent a 6.5-h light exposure session in one of three randomly assigned conditions: 1) continuous bright light of approximately 9,500 lux, 2) intermittent bright light (six 15-min bright light pulses of approximately 9,500 lux separated by 60 min of very dim light of <1 lux), and 3) continuous very dim light of <1 lux. Twenty subjects were included in the analysis. Core body temperature (CBT) and melatonin were used as phase markers of the circadian pacemaker. Phase delays of CBT and melatonin rhythms in response to intermittent bright light pulses were comparable to those measured after continuous bright light exposure, even though the total exposure to the intermittent bright light represented only 23% of the 6.5-h continuous exposure. These results demonstrate that a single sequence of intermittent bright light pulses can phase delay the human circadian pacemaker and show that intermittent pulses have a greater resetting efficacy on a per minute basis than does continuous exposure.     

Rapid in Vitro Assembly of Caulobacter crescentus FtsZ Protein at pH 6.5 and 7.2

FtsZ from most bacteria assembles rapidly in vitro, reaching a steady-state plateau in 5–10 s after addition of GTP. A recent study used a novel dynamic light-scattering technique to assay the assembly of FtsZ from Caulobacter crescentus (CcFtsZ) and reported that assembly required 10 min, ∼100 times slower than for related bacteria. Previous studies had indicated normal, rapid assembly of CcFtsZ. We have reinvestigated the assembly kinetics using a mutant L72W, where assembly of subunits into protofilaments results in a significant increase in tryptophan fluorescence. We found that assembly reached a plateau in 5–10 s and showed no change in the following 10 min. This was confirmed by 90° light scattering and negative-stain electron microscopy. The very slow kinetics in the dynamic light-scattering study may be related to a refractory state induced when the FtsZ protein is stored without nucleotide, a phenomenon that we had observed in a previous study of EcFtsZ. We conclude that CcFtsZ is not an outlier, but shows rapid assembly kinetics similar to FtsZ from related bacteria.     

Characterization and Effect of Light on the Plasma Membrane H+-ATPase of Bean Leaves

Proton excretion from bean (Phaseolus vulgaris L.) leaf cells is increased by bright white light. To test whether this could be due, at least in part, to an increase in plasma membrane (PM) ATPase activity, PM vesicles were isolated from primary leaves by phase partitioning and used to characterize PM ATPase activity and changes in response to light. ATPase activity was characterized as magnesium ion dependent, vanadate sensitive, and slightly stimulated by potassium chloride. The pH optimum was 6.5, the K_m was approximately 0.30 millimolar ATP, and the activity was about 60% latent. PM vesicles were prepared from leaves of plants grown for 11 days in dim red light (growing slowly) or grown for 10 days in dim red light and then transferred to bright white-light for 1 day (growing rapidly). For both light treatments, ATPase specific activity was approximately 600 to 700 nanomoles per milligram protein per minute, and the latency, K_m, and sensitivity to potassium chloride were also similar. PM vesicles from plants grown in complete darkness, however, exhibited a twofold greater specific activity. We conclude that the promotion of leaf growth and proton excretion by bright white light is not due to an increase in ATPase specific activity. Light does influence ATPase activity, however; both dim red light and bright white light decreased the ATPase specific activity by nearly 50% as compared with dark-grown leaves.     

Magnetic orientation in birds: non-compass responses under monochromatic light of increased intensity

Migratory Australian silvereyes (Zosterops lateralis) were tested under monochromatic light at wavelengths of 424 nm blue and 565 nm green. At a low light level of 7 x 10(15) quanta m(-2) s(-1) in the local geomagnetic field, the birds preferred their seasonally appropriate southern migratory direction under both wavelengths. Their reversal of headings when the vertical component of the magnetic field was inverted indicated normal use of the avian inclination compass. A higher light intensity of 43 x 10(15) quanta m(-2) s(-1), however, caused a fundamental change in behaviour: under bright blue, the silvereyes showed an axial tendency along the east-west axis; under bright green, they showed a unimodal preference of a west-northwesterly direction that followed a shift in magnetic north, but was not reversed by inverting the vertical component of the magnetic field. Hence it is not based on the inclination compass. The change in behaviour at higher light intensities suggests a complex interaction between at least two receptors. The polar nature of the response under bright green cannot be explained by the current models of light-dependent magnetoreception and will lead to new considerations on these receptive processes.     

Dynamic resetting of the human circadian pacemaker by intermittent bright light

In humans, experimental studies of circadian resetting typically have been limited to lengthy episodes of exposure to continuous bright light. To evaluate the time course of the human endogenous circadian pacemaker's resetting response to brief episodes of intermittent bright light, we studied 16 subjects assigned to one of two intermittent lighting conditions in which the subjects were presented with intermittent episodes of bright-light exposure at 25- or 90-min intervals. The effective duration of bright-light exposure was 31% or 63% compared with a continuous 5-h bright-light stimulus. Exposure to intermittent bright light elicited almost as great a resetting response compared with 5 h of continuous bright light. We conclude that exposure to intermittent bright light produces robust phase shifts of the endogenous circadian pacemaker. Furthermore, these results demonstrate that humans, like other species, exhibit an enhanced sensitivity to the initial minutes of bright-light exposure.     

Light-Scattering Spectrum Due to Wiggling Motions of Bacteria

Simple models are used to calculate the inelastic light scattering spectrum of motile bacteria when wiggling motions are included in addition to translational displacement. Computations of spectra lead to the conclusion that nontranslational motions can be neglected when swimming speeds are deduced from light-scattering data for normal vigorously motile strains. On the other hand, for slowly translating bacteria, or for strains exhibiting noticeable wiggling motion when viewed in a microscope, additional spectral components may be significant. Such components are best distinguished when measurements are made at small and intermediate scattering angles; at large angles the spectra have approximately the same scaling properties (functionals of Qt, Q being the Bragg wave vector) as those associated with simple translational motility.     

The effect of light on morphogenesis of Dictyostelium mucoroides

The effect of light on the production of macrocysts and sorocarps of Dictyostelium mucoroides, strain DM-7, has been studied with surface cultures grown on dilute lactose-peptone agar at 22 degrees C with Escherichia coli, strain B/r, as food bacteria. The production of sorocarps or macrocysts can be controlled by altering the light component of the environment. Far red light had no effect on macrocyst production, whereas visible light from 440 to 700 nm inhibited macrocyst production with production decreasing with increasing light intensity. Fluence response curves for macrocyst production were determined for twelve wavelengths of light between 400 and 700 nm. An action spectrum calculated from the fluence response curves shows a single major peak at about 425-430 nm.     

Insect pupil mechanisms

Summary The spectral characteristics of the pupil mechanism in blowfly photoreceptors and their dependence on light intensity have been investigated together with the intensity dependence of the receptor potential. The threshold for the pupil response as measured by reflectance is found at an intensity at which the peak of the receptor potential is about half maximal and the plateau potential starts to saturate. The reflectance saturates at about 3 log-units above threshold. The reflectance spectrum peaks near 620 nm, and its shape is independent of adaptation intensity. The absorbance change, measured by transmission, is extreme in the blue, at about 470 nm. The shape of the absorbance spectrum is slightly intensity dependent, presumably due to optical waveguide effects. The dynamic ranges of the light-induced reflectance and absorbance changes do not coincide. The reflectance change shows saturation at least 1 to 1.5 log units before the absorbance change saturates.     

NADH-synergism of NADPH-dependent o-dealkylation of type II compounds, p-anisidine and p-phenetidine, in rat liver microsomes.

When fresh citrated platelet-rich plasma was stirred at 900 rpm, stopping the stirrer increased the extinction, E (optical density, absorbance), of the plasma by 25%. After the platelets from humans or rabbits had changed shape on the addition of ADP, stopping the stirrer increased E by only about 2%. Assuming the shape of a platelet to approximate an ellipsoid of revolution which is originally flat and becomes more or less spherical after ADP, the effects of stirring on extinction are accounted for with conventional light-scattering theory. The change in extinction caused by stirring is the basis of a proposed nondestructive and remote assay of platelet shape. Extinction changes induced by chlorpromazine, which causes disk-sphere transformation only, are found to agree with theoretical predictions based on the shape change. The effects of ADP, which also produces pseudopods, are systematically smaller. The optical effects of shape and pseudopods can be separated: those of shape are sensitive to stirring, while those of pseudopods are not. ADP evidently produces a 37% increase in extinction of stirred platelets due to disk-sphere transformation plus a 9% decrease due to pseudopod formation (net increase, 28%). With simplified models of pseudopods, light-scattering theory is found to confirm that pseudopod formation should cause a decrease in extinction and total light scattering.     

Effect of change in concentration upon lens turbidity as predicted by the random fluctuation theory.

Theoretical calculations were performed to predict how the light scattering intensity would change with changes in concentration in the gel state. The theory of light scattering was applied to a random distribution of hard spheres. The spherical particles with constant diameter were embedded in a medium having a different refractive index. The light-scattering intensities obtained as a function of concentration showed that in dilute solutions the scattered light intensity increases with concentration. However, in concentrated solution greater than 0.1 or 0.2 volume fraction, the light-scattering intensity decreases with increase in concentration.     

Antidepressant effects of mono- and combined non-drug treatments for seasonal and non-seasonal depression

The involvement of chronobiological mechanisms in the antidepressant response to such non-drug treatments as bright light, physical exercise and sleep deprivation still remain to be clarified. We compare the efficacy of several treatment strategies for seasonal and non-seasonal depression and discuss possible the contribution of chronobiological and psychological mechanisms in antidepressant response. The therapeutic effects were tested at the medical academic hospital near Novosibirsk (55 degrees North) in 138 subjects, either with winter depression or with non-seasonal depression or without depression (n = 41, 64 and 33, respectively). One-week monotreatments were either 2-hour 2500 lux cool-white incandescent light from 14:00 (n = 9, 9, 9, respectively) or 1-hour physical exercise from 13:00 (n = 9, 9, 9, respectively). One-week combined treatments included a night of total sleep deprivation followed by either 2-hour bright light from 14:00 (n = 8, 12, 0, respectively) or 1-hour physical exercise either under ordinary room light from 13:00 (n = 0, 12, 0, respectively) or under bright light from 12:00 (n = 5, 11, 0, respectively). The results indicate that, in subjects left without antidepressant treatment for a week (n = 10, 11, and 15, respectively), the 21-item Hamilton Depression Rating Scale score did not change significantly. The beneficial effects of total sleep deprivation were similar in seasonal and non-seasonal depression. The seasonals exhibited better response to bright light compared to non-seasonals. After sleep deprivation the substantial further improvements were produced by either lighting or exercising. Compared to the patients exercising under ordinary room light, the patients exercising under bright light did not gain an additional benefit. In general, winter depression was well-treated with either exercise or light, while the most promising treatment for non-seasonal depression was physical exercise combined with sleep deprivation. Bright light or physical exercise administered in the middle of the day were not less favorable compared to the treatments in the morning hours, although it is unlikely that they considerably challenged patient's chronobiology. It was concluded that the placebo effect would account for a large portion of clinical response to open non-pharmacological treatments. Therapeutic hops and visibility of such treatments would explain their high antidepressant efficacy in comparison with pharmacological trials applying a double blind cross-over design. In particular, the excellent response of patients with winter depression to light therapy might be related to their tendency to attribute a high symbolic value to bright light and associate their bad mood with a dark season.     

Bright artificial light produces subsensitivity to nicotine

Bright artificial light is a treatment for seasonal depression. Eleven (11) rats were exposed to bright artificial light (11,500 lux) for two consecutive weeks. The thermic response to nicotine was measured prior to light exposure and after one and two weeks of treatment. The thermic response to nicotine at baseline was -1.69 +/- 0.25 degrees C (mean +/- SEM). The thermic response to nicotine was -0.66 +/- 0.12 degrees C (p less than 0.002) after one and +0.31 +/- 0.14 degrees C (p less than 0.000025) after two weeks of light exposure. The change in temperature was different between weeks one and two (p less than 0.000025). The exposure of animals to constant light at an intensity of 300 lux did not blunt the hypothermic response to nicotine. These findings suggest that bright artificial light, like other antidepressant treatments, produces subsensitivity of a nicotinic mechanism involved in the regulation of core temperature.     

Ultraviolet-Induced Sensitivity to Visible Light in Ultraviolet Receptors of Limulus

In the UV-sensitive photoreceptors of the median ocellus (UV cells), prolonged depolarizing afterpotentials are seen following a bright UV stimulus. These afterpotentials are abolished by long-wavelength light. During a bright UV stimulus, long-wavelength light elicits a sustained negative-going response. These responses to long-wavelength light are called repolarizing responses. The spectral sensitivity curve for the repolarizing responses peaks at 480 nm; it is the only spectral sensitivity curve for a median ocellus electrical response known to peak at 480 nm. The reversal potentials of the repolarizing response and the depolarizing receptor potential are the same, and change in the same way when the external sodium ion concentration is reduced. We propose that the generation of repolarizing responses involves a thermally stable intermediate of the UV-sensitive photopigment of UV cells.