scholarly journals Direct Action of Light in Naturally Pigmented Muscle Fibers

1962 ◽  
Vol 46 (2) ◽  
pp. 333-342 ◽  
Author(s):  
Howard H. Seliger
Keyword(s):  
Visual Pigment ◽  
Absorption Maximum ◽  
Pupil Diameter ◽  
Direct Action ◽  
Pigment Epithelium ◽  
Action Spectrum ◽  
Square Root ◽  
Light Reaction ◽  
First Order ◽  
Iris Sphincter

Contraction due to light in excised eel irises appears to follow a simple first order law. The action spectrum for contraction has a maximum which agrees with the eel rhodopsin absorption maximum. Inasmuch as rhodopsin is the rod pigment-opsin complex and the iris sphincter pupillae evolves from the pigment epithelium of the retina in the region of the iris, the muscle pigment might be the same as the visual pigment. In the human eye the contraction of the iris sphincter is activated only by light incident on the retina and the pupil diameter varies inversely with the square root of the light intensity. The inverse first power relation observed in the present experiments suggests a more primitive origin for the light reaction in eel irises. Relaxation is a much slower process and can be approximated as the sum of two first order processes.

scholarly journals Dependency on light and vitamin A derivatives of the biogenesis of 3-hydroxyretinal and visual pigment in the compound eyes of Drosophila melanogaster.

1988 ◽  
Vol 92 (5) ◽  
pp. 587-600 ◽  
Author(s):  
K Isono ◽  
T Tanimura ◽  
Y Oda ◽  
Y Tsukahara
Keyword(s):  
Drosophila Melanogaster ◽  
Vitamin A ◽  
Visual Pigment ◽  
Absorption Maximum ◽  
Action Spectrum ◽  
Compound Eyes ◽  
Trans Form ◽  
Optimum Wavelength ◽  
Derivatives Of ◽  
Cis Isomer

When the fruitfly, Drosophila melanogaster, was reared on media deficient in carotenoids and retinoids, the level of 3-hydroxyretinal (the chromophore of fly rhodopsin) in the retina decreased to less than 1% compared with normal flies. The level of 3-hydroxyretinal increased markedly in flies that were given a diet supplemented with retinoids or carotenoids. The retinas of flies fed on all-trans retinoids and maintained in the dark predominantly contained the all-trans form of 3-hydroxyretinal, and showed no increase in the level of either the 11-cis isomer or the visual pigment. Subsequent illumination of the flies converted substantial amounts of all-trans 3-hydroxyretinal to its 11-cis isomer. The action spectrum of the conversion by illumination showed the optimum wavelength to be approximately 420 nm, which is significantly greater than the absorption maximum of free, all-trans 3-hydroxyretinal. Flies that were fed on carotenoids showed a rapid increase of the levels of 11-cis 3-hydroxyretinal and of visual pigment in the absence of light.

scholarly journals New Mathematical Modeling Approach for Predicting Microbial Inactivation by High Hydrostatic Pressure

2007 ◽  
Vol 73 (8) ◽  
pp. 2468-2478 ◽  
Author(s):  
Bernadette Klotz ◽  
D. Leo Pyle ◽  
Bernard M. Mackey
Keyword(s):  
Microbial Inactivation ◽  
Inactivation Kinetics ◽  
Published Data ◽  
Model Parameters ◽  
Order Kinetic ◽  
Square Root ◽  
Additional Time ◽  
Decimal Reduction Time ◽  
First Order ◽  
Primary Model

ABSTRACT A new primary model based on a thermodynamically consistent first-order kinetic approach was constructed to describe non-log-linear inactivation kinetics of pressure-treated bacteria. The model assumes a first-order process in which the specific inactivation rate changes inversely with the square root of time. The model gave reasonable fits to experimental data over six to seven orders of magnitude. It was also tested on 138 published data sets and provided good fits in about 70% of cases in which the shape of the curve followed the typical convex upward form. In the remainder of published examples, curves contained additional shoulder regions or extended tail regions. Curves with shoulders could be accommodated by including an additional time delay parameter and curves with tails shoulders could be accommodated by omitting points in the tail beyond the point at which survival levels remained more or less constant. The model parameters varied regularly with pressure, which may reflect a genuine mechanistic basis for the model. This property also allowed the calculation of (a) parameters analogous to the decimal reduction time D and z, the temperature increase needed to change the D value by a factor of 10, in thermal processing, and hence the processing conditions needed to attain a desired level of inactivation; and (b) the apparent thermodynamic volumes of activation associated with the lethal events. The hypothesis that inactivation rates changed as a function of the square root of time would be consistent with a diffusion-limited process.

Multiple cell targets for melatonin action in Xenopus laevis retina: Distribution of melatonin receptor immunoreactivity

2001 ◽  
Vol 18 (5) ◽  
pp. 695-702 ◽  
Author(s):  
ALLAN F. WIECHMANN ◽  
CELESTE R. WIRSIG-WIECHMANN
Keyword(s):  
Xenopus Laevis ◽  
Direct Action ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Plexiform Layer ◽  
Amacrine Cells ◽  
Receptor Protein ◽  
Inner Plexiform Layer ◽  
Melatonin Receptor ◽  
Multiple Cell

In the retina of the African clawed frog (Xenopus laevis), melatonin is synthesized by the photoreceptors at night, and binds to receptors that likely mediate paracrine responses. Melatonin appears to alter the sensitivity of the retinal cells to light, and may play a key role in regulating important circadian events that occur in the eye. A polyclonal antibody was raised against a 13 amino acid peptide corresponding to a region of the third cytoplasmic loop of the Xenopus laevis Mel1c melatonin receptor. Western blot analysis revealed a major immunoreactive band of approximately 60 kD in neural retina and retinal pigment epithelium (RPE) membranes. Immunocytochemical labeling of sections of Xenopus eyes demonstrated intense melatonin receptor-like immunoreactivity in the inner plexiform layer (IPL). Immunolabeling with antibodies to glutamate decarboxylase (GAD) or tyrosine hydroxylase (TOH) appeared to co-localize with the melatonin receptor immunoreactivity in different sublaminas of the IPL. This suggests that both GABAergic and dopaminergic amacrine cells express melatonin receptor protein. There were also some melatonin receptor immunoreactive varicose fibers in the IPL that did not co-localize with either TOH or GAD, and may represent efferent fibers, since they could be followed into the optic nerve. Melatonin receptor immunoreactivity was also present on cell soma in the ganglion cell layer. Furthermore, a moderate level of melatonin receptor immunoreactivity was observed in the RPE and rod and cone photoreceptor cells. The presence of melatonin receptor immunoreactivity in these cells supports previous observations of melatonin receptor RNA expression in multiple cell types in the Xenopus retina. Expression of melatonin receptor protein in the photoreceptors suggests that melatonin may have a direct action on these cells.

scholarly journals Peropsin, a novel visual pigment-like protein located in the apical microvilli of the retinal pigment epithelium

1997 ◽  
Vol 94 (18) ◽  
pp. 9893-9898 ◽  
Author(s):  
H. Sun ◽  
D. J. Gilbert ◽  
N. G. Copeland ◽  
N. A. Jenkins ◽  
J. Nathans
Keyword(s):  
Retinal Pigment Epithelium ◽  
Visual Pigment ◽  
Pigment Epithelium ◽  
Retinal Pigment

The effect of extrinsic factors on two distinctive rhodopsin–porphyropsin systems

1977 ◽  
Vol 55 (6) ◽  
pp. 1000-1009 ◽  
Author(s):  
William N. McFarland ◽  
Donald M. Allen
Keyword(s):  
Visual Pigment ◽  
Brook Trout ◽  
Pigment Epithelium ◽  
Cold Treatment ◽  
Continuous Light ◽  
Photoreceptor Cells ◽  
Pigment Composition ◽  
Extrinsic Factors ◽  
Treatment Groups ◽  
Species Groups

The effects of light, temperature, and thyroxine on the proportions of two visual pigments (rhodopsin and porphyropsin) are compared for three species of fishes in which the pigment proportions change oppositely in response to light (rainbow and brook trout vs. common shiners). In rainbow trout and common shiners higher temperatures reduced the proportions of porphyropsin in the retina, independent of photic conditions. The greatest differences between the warm and cold treatment groups, however, were obtained with a photoperiod as contrasted with continuous light or darkness. Capping of one eye in brook trout reduced porphyropsin independently of the uncapped eye. Thyroxine, which favors porphyropsin in both species groups, acted effectively only in the presence of light. It is suggested that a photoperiod, which produces both bleaching and photomechanical movements within the retina, enhances the exchange of vitamin A1 and A2 aldehydes between the photoreceptor cells and the pigment epithelium. Apparently light influences these processes oppositely in the different groups of fishes. A model to explain how photic conditions affect visual pigment composition in tadpoles (Bridges 1975) is extended to account for the opposite responses to light and darkness observed in different fishes.

Improved Electronically-Tunable Current-Mode Square-Root-Domain First-Order Multifunction Filter

2021 ◽  
pp. 2150190
Author(s):  
Manoj Kumar Jain
Keyword(s):  
Transient Response ◽  
Current Mode ◽  
Square Root ◽  
Spice Simulation ◽  
First Order ◽  
Low Pass ◽  
Multifunction Filter ◽  
Simulation Results ◽  
Electronically Tunable ◽  
High Pass

Some time back, Kircay reported an electronically-tunable current-mode square-root-domain first-order filter capable of realizing low-pass (LP), high-pass (HP) and all-pass (AP) filter functions. When simulated in SPICE, Kircay’s circuit has been found to exhibit DC offsets in case of LP and AP responses and incorrect transient response in case of HP response. In this paper, an improved circuit overcoming these difficulties/deficiencies has been suggested and its workability of the improved circuit as well as its capability in meeting the intended objectives has been demonstrated by SPICE simulation results.

Selective utilization of serum vitamin A for visual pigment synthesis

1989 ◽  
Vol 142 (1) ◽  
pp. 207-214
Author(s):  
A. T. Tsin ◽  
S. N. Gentles ◽  
E. A. Castillo
Keyword(s):  
Vitamin A ◽  
Visual Pigment ◽  
Carassius Auratus ◽  
High Performance ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Serum Vitamin ◽  
Pigment Synthesis ◽  
Goldfish Carassius Auratus ◽  
Vitamin A2

Two groups of goldfish (Carassius auratus) were subjected to light and temperature conditions known to promote a contrast in their scotopic visual pigment compositions. After 3 weeks, the porphyropsin/rhodopsin ratio in the neuroretina of these goldfish ranged from 99% porphyropsin in one group to 59% in the other. Samples of blood, liver and retinal pigment epithelium (RPE) were also removed from these animals and analysed by high-performance liquid chromatography (HPLC) for vitamin A composition. There was consistently more vitamin A2 than vitamin A1 (over 50% vitamin A2) in both vitamin A alcohol and vitamin A esters extracted from the liver and the RPE. In contrast, only 30% of all vitamin A extracted from the blood was vitamin A2. These observations suggest that it is mainly vitamin A1 that is transported in the blood, whereas vitamin A2 is selectively retained in the liver and in the RPE and used to form porphyropsin in the eye.

Suppression of cone-driven responses by rods in the isolated frog retina

1988 ◽  
Vol 1 (4) ◽  
pp. 331-338 ◽  
Author(s):  
Cun-Jian Dong ◽  
Hao-Hua Qian ◽  
John S. McReynolds ◽  
Xiong-Li Yang ◽  
Yu-Min Liu
Keyword(s):  
Dark Adaptation ◽  
Visual Pigment ◽  
Pigment Epithelium ◽  
Signal Transmission ◽  
Receptor Potential ◽  
Response Sensitivity ◽  
Long Wavelength ◽  
Negligible Amount ◽  
Frog Retina ◽  
Time Courses

AbstractThe sensitivity of rod- and cone-driven responses was studied in the isolated frog retina during the period of rapid dark adaptation following a conditioning flash which bleached a negligible amount of visual pigment. Following a conditioning flash, cone-driven b-wave responses were first enhanced and then depressed. The time courses of the enhancement and subsequent depression of cone-drive responses varies greatly with the intensity and wavelength of the conditioning flash, but were identical when the conditioning' flashes were matched for equal excitation of 502 nm rods. These changes in cone-driven response sensitivity were correlated with the desensitization and recovery of rods following the conditioning flash. When signal transmission from rods to second-order cells was interrupted by the addition of L-glutamate, the conditioning flash did not produce the above-described enhancement and subsequent depression of long-wavelength receptor potential responses. The suppression of cone-driven response therefore appears to be due to a synaptically mediated influence from 502 nm rods which is maximal when the rods are in the dark-adapted state, with little or no contribution from 433 nm rods, and no involvement of the pigment epithelium.

Kinetics and mechanism of the hexacyanomanganate(IV)–arsenic(III) redox reaction in acidic medium

1988 ◽  
Vol 66 (11) ◽  
pp. 2855-2859 ◽  
Author(s):  
Guillermo López-Cuetoa ◽  
Carlos Ubide
Keyword(s):  
Sulfuric Acid ◽  
Ionic Strength ◽  
Rate Constant ◽  
Redox Reaction ◽  
Acidic Medium ◽  
Absorption Maximum ◽  
Cyanide Complex ◽  
Acidic Media ◽  
Acid Media ◽  
First Order

The reaction between hexacyanomanganate(IV) and arsenic(III), in acidic media, proceeds with a stoichiometry Δ[Mn(IV)]/Δ[As(III)] = 1. The reaction in sulfuric acid media has been followed spectrophotometrically at 387 nm, where the Mn(IV) cyanide complex has an absorption maximum, and shows a first-order dependence on the hexacyanomanganate(IV) concentration, viz., −d[Mn(IV)]/dt = k[Mn(IV)], the value of k being dependent on the acidity and the arsenic(III) concentration. At As(III), 0.1 M; H+, 0.16 M; ionic strength, 2.0; and T, 30 °C, the value of the rate constant was found to be k = (1.04 ± 0.06) × 10−5 s−1. The proposed mechanism, through three parallel pathways, explains satisfactorily the experimental results observed.

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