SENSITIVITY OF MOUSE SKH:HR-2 TO ULTRAVIOLET LIGHT: MOUSE PIGMENTATION MODEL

Abstract— The mouse Skh:HR-2 has been reported to be sensitized to ultraviolet light and become pigmented. Using three independent parameters associated with pigmentation. we have examined the ability of the mouse to become pigmented. The methods utilized were spectroscopic (skin color). histological (melanocyte density and epidermal thickness), and biochemical (tyrosinase activity). Following a two-week ultraviolet exposure, the mice were pigmented with the degree of pigment change related to the ultraviolet dose administered. Perturbations in skin color, epidermal thickness, melanocyte density, and tyrosinase activity were recorded. Mice were also examincd for their response to tyrosinc applied topically following each ultraviolet exposure. With the exccption of epidermal thickness. all the pigmentation parameters were accentuated when compared to results from ultraviolet exposure alone.     

Comparative study of the dark and light-induced toxicity of lipofuscin granules from human retinal pigment epithelium and their chromophore A2E on the cardiolipin liposome model

The damaging effect of lipofuscin granules from the human retinal pigment epithelium and fluorophore A2E was studied on models of calcein- and ascorbate-loaded cardiolipin liposomes and outer segments of the bovine eye photoreceptor cells in dark and under visible light irradiation. In dark fluorophore A2E induces the release of calcein from calcein-loaded liposomes and reduces the lifetime of the artificial bilayer lipid membrane prepared from dioleyl phosphatidilcholine. A similar detergent-like action A2E exhibits towards ascorbate-loaded liposomes, significantly accelerating the release of ascorbate in dark. In the presence of A2E, irradiation with the full visible light (390?C700 nm) stimulates both the release of ascorbate from liposomes and accelerates the destruction of the bilayer lipid membrane. Retinal pigment epithelium lipofuscin granules also accelerate the release of ascorbate from ascorbate-loaded liposomes under visible light irradiation; the blue light (457.9 nm) was twice as more efficient as the green light (514.5 nm). The preliminary irradiation of A2E with the visible light decreases its detergent-like action on the cardiolipin liposomal membranes under the dark conditions and the photosensitizing effect on the lipid peroxidation of the outer segments of photoreceptor cells. Unlike A2E, the visible light irradiation of a suspension of lipofuscin granules under similar conditions does not noticeably decrease their sensitizing activity towards lipid peroxidation. It is assumed that the phototoxicity of retinal pigment epithelium lipofuscin granules is related not only to A2E in their composition, but depends mainly on the content of other photosensitizers (chromophores) in the granules.     

DETERMINATION OF THE IN VIVO ABSORPTION AND PHOTOSYNTHETIC PROPERTIES OF THE LICHEN Acarospora schleicheri USING PHOTO ACOUSTIC SPECTROSCOPY

Photoacoustic spectroscopy was used to determine the in vivo spectra of the stratified components of the lichen Acarospora schleicheri. There were three pigmented layers observed by the photoacoustic method: an absorption band associated with the pigment rhizocarpic acid, a bulk cytochrome absorption, and the absorption of the algal chloroplast. Due to the different absorption properties of these distinct layers, the photoacoustic technique was able to monitor the physical effect of hydration on the lichen. Hydration of the lichen reduced the scatter of the sample, increasing the effective incident light intensity within the sample. Hydration also resulted in an increase in the optical absorption coefficient of the algal layer, which was interpreted as a movement of the algal chloroplast in response to low light fluence and hydrated conditions. The photoacoustic technique was also used to monitor the relative photosynthetic activity of the algae within the lichen in a hydrated and dehydrated state. The photosynthetic assay could detect photosynthetic activity in the hydrated state but not in the dehydrated state. In addition, the photosynthetic response was found to be induced and repressed with light and dark periods respectively and its detection was limited at high frequencies by the damping of the thermal wave from the algal layer.     

Nitric oxide-dependent pigment migration induced by ultraviolet radiation in retinal pigment cells of the crab Neohelice granulata

The purpose of this study was to verify the occurrence of pigment dispersion in retinal pigment cells exposed to UVA and UVB radiation, and to investigate the possible participation of a nitric oxide (NO) pathway. Retinal pigment cells from Neohelice granulata were obtained by cellular dissociation. Cells were analyzed for 30 min in the dark (control) and then exposed to 1.1 and 3.3 J cm⁻² UVA, 0.07 and 0.9 J cm⁻² UVB, 20 n m β-PDH (pigment dispersing hormone) or 10 μ m SIN-1 (NO donor). Histological analyses were performed to verify the UV effect in vivo . Cultured cells were exposed to 250 μ m L-NAME (NO synthase blocker) and afterwards were treated with UVA, UVB or β-PDH. The retinal cells in culture displayed significant pigment dispersion in response to UVA, UVB and β-PDH. The same responses to UVA and UVB were observed in vivo . SIN-1 did not induce pigment dispersion in the cell cultures. l-NAME significantly decreased the pigment dispersion induced by UVA and UVB but not by β-PDH. All retinal cells showed an immunopositive reaction against neuronal nitric oxide synthases. Therefore, UVA and UVB radiation are capable of inducing pigment dispersion in retinal pigment cells of Neohelice granulata and this dispersion may be nitric oxide synthase dependent.     

核桃外果皮中棕褐色色素的提取及性质测试

以水为萃取剂,提取晾干的核桃外果皮中棕褐色色素并对其稳定性进行了测试,结果表明,该色素水溶性好,耐热性,耐光性较好。盐、柠檬酸,金属离子对色素的色泽无不良影响,乙醇有增色效应,但易被H2O2氧化逐渐脱色,提取该色素工艺简单,无污染。     

THE EFFECT OF LIGHT ON THE OCELLAR PIGMENT OF SPIROCODON, AN ANTHOMEDUSA

Abstract— The ocellar pigment of Spirocodon saltatrix was extracted with 2% mildly alkaline cetyltrimethylammonium bromide (CTAB) and 90% methanol acidified with HCl. In the case of CTAB-extracted pigment, maximum changes in optical density upon illumination occurred in mildly alkaline media under aerobic conditions and in neutral media under anaerobic conditions. The density spectrum of the sample illuminated under anaerobic conditions closely resembled that of the reduced form of the pigment illuminated in the presence of air. When reduced in darkness, the pigment became photostable and its density spectrum differed from that of the pigment reduced after illumination. On aeration of the pigment solution illuminated under anaerobic conditions, its density spectrum in the visible range became similar to that of the pigment illuminated in the presence of air. A trace of air dissolved in experimental media caused auto-oxidation of the reduced form, during the process of which a definite isosbestic point was observed at 480 mμ. Under anaerobic conditions, short period of illumination produced changes in spectral absorbance only in the visible range. Changes in the u.v. range required longer exposures. The pigment extracted with acidified methanol was readily auto-oxidizable and it was the reduced form which showed photosensitivity, though the degree of sensitivity was extremely low. The density spectrum of illuminated pigment resembled that of the oxidized form. From these experiments, a tentative scheme involving an electron transfer system has been suggested for the chain of photic reaction of the anthomedusan ocellar pigment.     

Adrenocorticotropic Hormone and Cyclic Adenosine Monophosphate are Involved in the Control of Shark Bioluminescence

Among Etmopteridae and Dalatiidae, luminous species use hormonal control to regulate bioluminescence. Melatonin (MT) triggers light emission and, conversely, alpha melanocyte-stimulating hormone (α-MSH) actively reduces ongoing luminescence. Prolactin (PRL) acts differentially, triggering light emission in Etmopteridae and inhibiting it in Dalatiidae. Interestingly, these hormones are also known as regulators of skin pigment movements in vertebrates. One other hormone, the adrenocorticotropic hormone (ACTH), also members of the skin pigmentation regulators, is here pharmacologically tested on the light emission. Results show that ACTH inhibits luminescence in both families. Moreover, as MT and α-MSH/ACTH receptors are members of the G-protein coupled receptor (GPCR) family, we investigated the effect of hormonal treatments on the cAMP level of photophores through specific cAMP assays. Our results highlight the involvement of ACTH and cAMP in the control of light emission in sharks and suggest a functional similarity between skin pigment migration and luminescence control, this latter being mediated by pigment movements in the light organ-associated iris-like structure cells.     

PHOTOMOVEMENT RESPONSES OF THE HETEROTRICHOUS CILIATE Blepharisma Japonicum

Light-induced movement responses of the heterotrichous ciliate Blepharisma japonicum were studied by physiological experiments. Two photosensory responses could be identified. A step-up photophobic response is observed as a very rapid backward movement. Microbeam irradiations of individual cells showed that only the anterior part of the ciliate is able to perceive the light stimulus that mediates the phobic reaction. The action spectrum peaks at approximately 400 nm, which indicates that a blue light receptor is involved.
Positive photokinesis of Blepharisma could be shown as a forward movement that is accelerated by increasing the applied photon fluence rate. The steady state level of the velocity depends highly on wavelength and photon fluence rate of the actinic light. After specific inhibition of the phobic reaction bv 1 m/W NH₄⁺, photokinesis can be induced by microbeam irradiation at any part of the cell.
We isolated two main pigments by thin layer chromatography and characterized them as hypericin-like compounds: a red pigment that is obviously responsible for the red color of the ciliates (= blepharismin). and a yellow one with maximal absorption near 420 nm. The possible photoreceptor functions of these pigments are discussed.
We could not find in Blepharisma a distinct phototactic behavior which is so typical for the related ciliate Stentor.     

STUDIES ON THE RED AND BLUE FORMS OF THE PIGMENT OF BLEPHARISMA*

Abstract— –The intracellular pigment of the ciliate protozoan Blepharisma in the presence of oxygen sensitizes the cells to bright visible light (2700 foot candles (fc)). Illumination of the cells with dim visible light (200 fc) changes the color of the pigment to blue-gray; such cells are no longer sensitive to bright visible light. The pigment which exists in granules can be extruded by cold treatment and is slowly regenerated. The suspension of red cells, the extruded pigment from them and an ethanol extract of the pigment all have very similar absorption spectra. Illumination of the red pigment in ethanol converts it to the blue form of the pigment but only if oxygen is present, indicating a photooxidation. The pigment can be oxidized in darkness to the blue form by ozonation. A suspension of blue cells, the extruded pigment from them and an ethanol extract from them, all have similar absorption spectra. The pigments in red and blue form are very similar spectrophotometrically and in solubility in three species of Blepharisma studies: B. americanum, B. intermedium and B. japonicum. The purified pigment has strong absorption in the far (200–300 nm) ultraviolet (u.v.) and may serve as a screen against damaging U.V. radiation, especially as Blepharisma shows poor photoreactivation.     

LIGHT-CONTROLLED ADAPTATION KINETICS IN Phycomyces: EVIDENCE FOR A NOVEL YELLOW-LIGHT ABSORBING PIGMENT

When sporangiophores of the fungus Phycomyces blakesleeanus adapt from high to low fluence rate, dark adaptation (sensitivity recovery) can be accelerated by dim subliminal light [Galland et al. (1989) Photochem. Photobiol. 49, 485-491]. We measured fluence rate-response curves for this acceleration under the following conditions. After sporangiophores were initially adapted symmetrically to a fluence rate of 1 W m-2 (447 nm), they were exposed to unilateral subliminal light (subthreshold for phototropism) of variable wavelength and fluence rate, and then to unilateral test light (447 nm) of fluence rate either 10(-3) or 10(-5) W m-2. The duration of the subliminal light was chosen so that phototropism would not occur during this period. Phototropic latencies could be shortened by subliminal light that was less intense than the test light by several orders of magnitude. In experiments with the final unilateral light of fluence rate 10(-3) W m-2, the 447 nm subliminal light had a threshold (for the acceleration effect) of about 10(-11) W m-2. Yellow light of wavelength 575 nm, which itself is extremely ineffective for phototropism was extremely effective in shortening phototropic latencies in response in response to the test light. At 575 nm, the threshold was about 2 x 10(-12) W m-2. Conversely, near-UV light of wavelength 347 nm, which is highly effective for phototropism, was relatively ineffective (threshold approximately 7 x 10(-8) W m-2) in shortening the phototropic latency. Our results suggest the presence of a novel yellow-light absorbing pigment in Phycomyces that specifically regulates dark adaptation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cytotoxicity of All‐Trans‐Retinal Increases Upon Photodegradation†

All‐trans‐retinal (AtRal) can accumulate in the retina as a result of excessive exposure to light. The purpose of this study was to compare cytotoxicity of AtRal and photodegraded AtRal (dAtRal) on cultured human retinal pigment epithelial cells in dark and upon exposure to visible light. AtRal was degraded by exposure to visible light. Cytotoxicity was monitored by imaging of cell morphology, propidium iodide staining of cells with permeable plasma membrane and measurements of reductive activity of cells. Generation of singlet oxygen photosensitized by AtRal and dAtRal was monitored by time‐resolved measurements of characteristic singlet oxygen phosphorescence. Photodegradation of AtRal resulted in a decrease in absorption of visible light and accumulation of the degradation products with absorption maximum at ～330 nm. Toxicity of dAtRal was concentration‐dependent and was greater during irradiation with visible light than in dark. DAtRal was more cytotoxic than AtRal both in dark and during exposure to visible light. Photochemical properties of dAtRal indicate that it may be responsible for the maximum in the action spectra of retinal photodamage recorded in animals. In conclusion, photodegradation products of AtRal may impose a significant threat to the retina and therefore their roles in retinal pathology need to be explored.     

INTERACTION BETWEEN PHYTOCHROME AND THE BLUE LIGHT PHOTORECEPTOR SYSTEM IN Mougeotia*

Abstract— Face-to-profile chloroplast movement in Mougeotia was induced by sequences of strong blue and red short irradiations. This type of response occured only when blue light was applied prior to or simultaneously with red light, and far-red irradiation was necessary after the sequence to cancel the remaining gradient of the far-red absorbing form of phytochrome P_fr. The dependence of the response magnitude on blue and red light sequences was studied for a wide range of light durations and dark intervals. The relationship between the response and the dark interval points to the lack of direct coupling between phytochrome and blue-absorbing “cryptochrome”. It was postulated that a photoproduct having a life-time of2–3 min is formed by the blue-light-mediated reaction. This photoproduct interacts with phytochrome during its transformation or with its final P_fr form.     

ACTION SPECTRUM AND ELECTROPHYSIOLOGICAL RESPONSES CORRELATED WITH THE PHOTOPHOBIC RESPONSE OF STENTOR COERULEUS

Abstract— The blue-green ciliate. Stentor coeruleus , is found predominantly in shady places. This concentration occurs because stentor responds when swimming from a shaded area to a lighted area by reversing the direction of its ciliary beat and reorienting its swimming direction until it once again is in the shaded area. A graded receptor potential is recorded from microelectrodes in vacuoles of stentor when the animal is photically stimulated. For all but very weak stimuli this receptor potential is sufficient to elicit a regenerative transmembrane response of variable amplitude in a swimming animal. Suprathreshold electrical stimuli also elicit this regenerative response. In turn the regenerative response is coupled to ciliary reversal. Thus ciliary reversal appears to be produced whenever the photic receptor potential crosses the threshold for elicitation of the regenerative response.
Using the threshold for production of ciliary reversal as a criterion response, an action spectrum was obtained. This action spectrum correlates well with the absorption spectrum of the major pigment of S. coeruleus , stentorin. Stentor bleached of pigment also have an elevated threshold for ciliary reversal. Thus stentorin seems to be the photosensitive pigment in stentor responsible for its photophobic behavior.     

Evidence of microfilament-associated mitochondrial movement.

The mitochondria in the lower Malpighian tubule of the insect Rhodnius prolixus can be stimulated by feeding in vivo and by 5-hydroxytryptamine in vitro, to move from a position below the cell cortex to one inside the apical microvilli. During and following their movement into the microvilli, the mitochondria are intimately associated with the microfilaments of the cell cortex and microvillar core bundle. Bridges approximately 14 nm in length and 4 nm in diameter are observed connecting the microvillar microfilaments to the outer mitochondrial membrane and microvillar plasma membrane. Depolymerization of all visible microtubules with colchicine does not inhibit 5-HT-stimulated mitochondrial movement. On the other hand, treatment with cytochalasin B does block mitochondrial movement, suggesting that microfilaments play a role in the mitochondrial motility. We have labeled the microvillar microfilaments, which are 6 nm in diameter, with heavy meromyosin, which supports the contention that they contain actin. A model of the mechanism of mitochondrial movement is presented in which mitochondria slide into position in the microvilli along actin-containing microfilaments in a manner analogous to the sliding actin-myosin model of skeletal muscle.     

Phototaxis in Euglena. V. Photosuppression of phototactic activity by blue light

Abstract— The phototactic response of Euglena gracilis is suppressed when the organisms are exposed to bright light of wavelength less than 650 nm. Activity returns in the dark, approximately 40 min being required for full restoration. Action spectral measurements demonstrate that the receptor pigment which mediates the suppression response may be a flavoprotein. Evidence is presented which indicates that photosuppression involves a direct action on the photo-tactic apparatus, perhaps a photobleaching of the tactic photoreceptor pigment.     

PHOTOSENSORY TRANSDUCTION IN CILIATES. III. THE TEMPORAL RELATION BETWEEN MEMBRANE POTENTIALS AND PHOTOMOTILE RESPONSES IN Blepharisma japonic urn

Abstract— Blepharisma japonicum exhibits a step-up photophobic response when subjected to an increase in light stimulus intensity. This response is characterized by the stop reaction after a period of delay followed by backward swimming (lateral rotation). The latency of the stop response decreased and duration of the lateral rotation increased as the intensity of light stimuli was raised. A step-increase in light intensity elicited a graded membrane depolarization (photic receptor potential), as measured by intracellular microelectrode. When the amplitude of receptor potential exceeded a threshold depolarization for membrane excitation (15–25 mV), an all-or-none action potential of 50–65 mV in amplitude was evoked which also occurred with some latency. Light stimuli of higher intensity (suprathreshold) elicited action potential which was followed by a membrane after-depolarization. Increasing the intensity of stimuli caused generation of an action potential with shorter lag period and prolonged after-depolarization. The action spectra for the latency of stop reaction, receptor potential amplitude and cell photoresponsiveness showed maxima at 460, 530 and 580 nm. The analysis of temporal relationships between the electrophysiological responses and the motile events showed that latency of an action potential, induced by the receptor potential, correlates well with the latency of a cell stop response. Also the duration of membrane after-depolarization resembled the time period of the cell's backward swimming (cell rotation). The data obtained indicate that the primary reaction initiated by light absorption in the photoreceptor pigment (blepharismin) is converted into the observed electrical potential changes, which in turn results in the photomotile response of Blepharisma cells.     

Direct Measurements for Isomer Ratio of Retinal in Bacteriorhodopsin by an Electrochemical Method

Abstract— The composition of retinal isomers in bacteriorhodopsin (bR) in purple membrane (PM) was determined by photoelectric response measurements using a sandwich-type electrochemical cell. The measured amplitude of the photocurrent obtained from a dark-adapted sample was 55% lower than that from a light-adapted sample. This ratio, 55:45, would correspond to the 13- cis /aU- trans isomer ratio of retinal in the dark if the 13- cis form of the pigment did not give a response. This amplitude change correlated with the visible spectral shift of bR. The isomer ratio in the dark depended only weakly on the temperature of the electrolyte, whereas the retinal isomerization rate strongly depended on the temperature and the pH of the electrolyte in the cell. Our results indicate that photoelectric response is elicited only by a species originating from bR containing all- trans retinal and that the behavior of the response in the dark is associated with the pKa of the proton release kinetics of Asp-85.     

PHYSIOLOGICAL STUDIES ON PEA TENDRILS—X. CHARACTERIZATION OF THE LIGHT ACTIVATION EFFECT ON CONTACT COILING AS A BLUE LIGHT TRIGGER*

Abstract— Tendrils of the Alaska pea lose their capacity to coil in response to a mechanical stimulus between 24 and 48 h after being placed in the dark. Light is thereafter necessary for the motor response to proceed once the mechanical stimulus has becn sensed by dark-adapted tendrils. An action spectrum for this light activation effect showed that the most effective region of the visible spectrum was a narrow band in the blue region. Tendrils excised from their petiole and leaflets coiled more than any other preparation used. A linear relationship was found between the duration of post-stimulated white light treatment and the amount of coiling.     

A DIURNAL RHYTHM IN THE RATE OF LIGHT-INDUCED ELECTRON FLOW IN MAIZE BUNDLE SHEATH STRIPS

Abstract— A technique for the rapid mechanical isolation of bundle sheath strips from Zea mays was used to study the rate of light-induced electron flow as a function of time of day. Seedlings were raised for 10 days in light/dark cycles and then exposed to various intensities of light. The rate of light-induced electron flow was measured five times during the 24-h cycle using a whole cell, H₂O to methyl viologen assay in the presence of gramicidin. The uncoupled rate of electron flow reached a maximum at midday and then decreased for the remainder of the cycle.
If at the end of the 14-h dark period plants were either maintained in darkness, or exposed to very low irradiance white light. then no rhythmicity was observed. If continuous light at higher irradiance was used, then only one additional peak of activity was observed. The minimal light irradiance necessary to allow the continued expression of the rhythm in light/dark cycles is in the range between 11 to 54 W m_-2. A 15-min bright-light (54 W m_-2) pulse administered at dawn is not sufficient to stimulate the expression of the rhythm indicating that the light during the light/dark cycle is doing more than just acting as a "light-on" synchronizing signal. An imposed dark period is also necessary if the rhythm is to be expressed for more than one cycle.     

APPLICATION OF PHOTODYNAMIC OXIDATION TO THE DISINFECTION OF TAPWATER, SEA WATER, AND SEWAGE CONTAMINATED WITH POLIOVIRUS

Abstract. Poliovirus when added to tapwater, sewage or seawater was readily photoinactivated by methylene blue and visible light. Typically, almost 2.5 logs of virus could be inactivated upon a 5-min exposure to 670 nm light (20 W/m²) in solutions containing 13 μ M methylene blue at pH 10.0. A biphasic inactivation curve was produced for poliovirus, regardless of dye concentration, pH, temperature, sensitization time, nature of suspending solution or sequence of light exposure. These results indicated that a multi-hit inactivation event was occurring. Preincubation of the dye-virus mixture at 24°C increased the rate of virus photoinactivation. Dye concentrations above 26 μ M have little advantage in increasing the amount of virus photoinactivated. Significant inactivation of the virus in the dark occurred at high dye concentrations (52–130μ M ).