scholarly journals Light Adaptation in the Ventral Photoreceptor of Limulus

1974 ◽  
Vol 64 (2) ◽  
pp. 166-185 ◽  
Author(s):  
Richard Srebro ◽  
Michael Behbehani
Keyword(s):  
Time Course ◽  
Light Adaptation ◽  
Light Response ◽  
Slow Phase ◽  
Rapid Phase ◽  
Short Delay ◽  
Light Intensities ◽  
Lateral Eye ◽  
Complex Process ◽  
Two Phases

Light adaptation in both the ventral photoreceptor and the lateral eye photoreceptor is a complex process consisting of at least two phases. One phase, which we call the rapid phase of adaptation, occurs whenever there is temporal overlap of the discrete waves that compose a light response. The recovery from the rapid phase of adaptation follows an exponential time-course with a time constant of approximately 75 ms at 21°C. The rapid phase of adaptation occurs at light intensities barely above discrete wave threshold as well as at substantially higher light intensities with the same recovery time-course at all intensities. It occurs in voltage-clamped and unclamped photoreceptors. The kinetics of the rapid phase of adaptation is closely correlated to the photocurrent which appears to initiate it after a short delay. The rapid phase of adaptation is probably identical to what is called the "adapting bump" process. At light intensities greater than about 10 times discrete wave threshold another phase of light adaptation occurs. It develops slowly over a period of ½ s or so, and decays even more slowly over a period of several seconds. It is graded with light intensity and occurs in both voltage-clamped and unclamped photoreceptors. We call this the slow phase of light adaptation.

The Sensitivity of the Ventral Nerve Photoreceptor of Limulus Recovers after Light Adaptation in Two Phases of Dark Adaptation

1986 ◽  
Vol 41 (5-6) ◽  
pp. 657-667 ◽  
Author(s):  
I. Claßen-Linke ◽  
H. Stieve
Keyword(s):  
Dark Adaptation ◽  
Time Course ◽  
Light Adaptation ◽  
Light Flash ◽  
Light Response ◽  
Receptor Potential ◽  
Second Phase ◽  
Two Phases ◽  
Ventral Nerve Photoreceptor ◽  
External Calcium

The time course of the recovery of the sensitivity of the Limulus ventral nerve photoreceptor was measured during dark adaptation following light adaptation by a bright 1 or 5 s illumination. The stimulus intensity ICR of a 300 μs light flash evoking a response of criterion amplitude (receptor potential or receptor current under voltage clamp conditions) was used as measure of sensitivity.The time course of dark adaptation shows two phases with time constants in the range of 5-9 s and 300-500 s (15 °C). Only the first of the two phases is significantly changed when the extracel- lular Ca2+-concentration is varied.The power function ICR = a·Io-tDA-b gives a good data fit for each of the two phases of dark adaptation. In the first phase the factor ax and the exponent bx are decreased when the external calcium is lowered from 10 mmol/1 to 250 μmol/1. Conversely a1 and b1 are increased when the Ca2+-concentration is raised to 40 mmol/1. For the second phase neither a2 nor b2 is changed significantly upon the changes in calcium concentration in the same experiments.The two phases of dark adaptation reflect the behaviour of the two components C1 and C2 of the electrical light response (receptor potential or receptor current). Under the conditions described here C, determines the size of the light response during the first phase of dark adaptation whereas C2 mainly influences the size of the response during the second phase.Interpretation: The fast first phase of dark adaptation is determined by the change in intracellu- lar Ca2+-concentration. The slower second phase of dark adaptation is not primarily calcium- controlled.

scholarly journals Two Temporal Phases of Light Adaptation in Retinal Rods

2002 ◽  
Vol 119 (2) ◽  
pp. 129-146 ◽  
Author(s):  
Peter D. Calvert ◽  
Victor I. Govardovskii ◽  
Vadim Y. Arshavsky ◽  
Clint L. Makino
Keyword(s):  
Binding Sites ◽  
Time Course ◽  
Light Adaptation ◽  
Dynamic Range ◽  
Continuous Illumination ◽  
Slow Phase ◽  
Fast Phase ◽  
Slow Adaptation ◽  
Adaptation Phase

Vertebrate rod photoreceptors adjust their sensitivity as they adapt during exposure to steady light. Light adaptation prevents the rod from saturating and significantly extends its dynamic range. We examined the time course of the onset of light adaptation in bullfrog rods and compared it with the projected onset of feedback reactions thought to underlie light adaptation on the molecular level. We found that adaptation developed in two distinct temporal phases: (1) a fast phase that operated within seconds after the onset of illumination, which is consistent with most previous reports of a 1–2-s time constant for the onset of adaptation; and (2) a slow phase that engaged over tens of seconds of continuous illumination. The fast phase desensitized the rods as much as 80-fold, and was observed at every light intensity tested. The slow phase was observed only at light intensities that suppressed more than half of the dark current. It provided an additional sensitivity loss of up to 40-fold before the rod saturated. Thus, rods achieved a total degree of adaptation of ∼3,000-fold. Although the fast adaptation is likely to originate from the well characterized Ca2+-dependent feedback mechanisms regulating the activities of several phototransduction cascade components, the molecular mechanism underlying slow adaptation is unclear. We tested the hypothesis that the slow adaptation phase is mediated by cGMP dissociation from noncatalytic binding sites on the cGMP phosphodiesterase, which has been shown to reduce the lifetime of activated phosphodiesterase in vitro. Although cGMP dissociated from the noncatalytic binding sites in intact rods with kinetics approximating that for the slow adaptation phase, this hypothesis was ruled out because the intensity of light required for cGMP dissociation far exceeded that required to evoke the slow phase. Other possible mechanisms are discussed.

scholarly journals Regulation of cGMP levels by guanylate cyclase in truncated frog rod outer segments.

1989 ◽  
Vol 94 (4) ◽  
pp. 649-668 ◽  
Author(s):  
S Kawamura ◽  
M Murakami
Keyword(s):  
Guanylate Cyclase ◽  
Outer Segment ◽  
Time Course ◽  
Light Adaptation ◽  
Light Response ◽  
Regulation Mechanism ◽  
Maximal Effect ◽  
Rod Outer Segment ◽  
Light Flashes ◽  
Dependent Mechanism

Cyclic GMP is the second messenger in phototransduction and regulates the photoreceptor current. In the present work, we tried to understand the regulation mechanism of cytoplasmic cGMP levels in frog photoreceptors by measuring the photoreceptor current using a truncated rod outer segment (tROS) preparation. Since exogenously applied substance diffuses into tROS from the truncated end, we could examine the biochemical reactions relating to the cGMP metabolism by manipulating the cytoplasmic chemical condition. In tROS, exogenously applied GTP produced a dark current whose amplitude was half-maximal at approximately 0.4 mM GTP. The conductance for this current was suppressed by light in a fashion similar to when it is activated by cGMP. In addition, no current was produced in the absence of Mg2+, which is known to be necessary for the guanylate cyclase activity. These results indicate that guanylate cyclase was present in tROS and synthesized cGMP from exogenously applied GTP. The enzyme activity was distributed throughout the rod outer segment. The amount of synthesized cGMP increased as the cytoplasmic Ca2+ concentration of tROS decreased, which indicated the activation of guanylate cyclase at low Ca2+ concentrations. Half-maximal effect of Ca2+ was observed at approximately 100 nM. tROS contained the proteins involved in the phototransduction mechanism and therefore, we could examine the regulation of the light response waveform by Ca2+. At low Ca2+ concentrations, the time course of the light response was speeded up probably because cGMP recovery was facilitated by activation of the cyclase. Then, if the cytoplasmic Ca2+ concentration of a photoreceptor decreases during light stimulation, the Ca2+ decrease may explain the acceleration of the light response during light adaptation. In tROS, however, we did observe an acceleration during repetitive light flashes when the cytoplasmic Ca2+ concentration increased during the stimulation. This result suggests the presence of an additional light-dependent mechanism that is responsible for the acceleration of the light response during light adaptation.

Ca2+, myosin phosphorylation, and relaxation of arterial smooth muscle

1983 ◽  
Vol 245 (3) ◽  
pp. C271-C277 ◽  
Author(s):  
W. T. Gerthoffer ◽  
R. A. Murphy
Keyword(s):  
Thin Filament ◽  
Time Course ◽  
Regulatory Mechanism ◽  
High Sensitivity ◽  
Slow Phase ◽  
Tetraacetic Acid ◽  
Rapid Phase ◽  
Cross Bridges ◽  
Resting Tone ◽  
Two Populations

Relaxation of tissues prepared from the swine carotid media following agonist (110 mM K+) washout was analyzed as a dual-exponential decay. The time course of the initial rapid phase (about 2 min) corresponded to myosin dephosphorylation and to the decay of the capacity to shorten isotonically. Because myosin was dephosphorylated to basal levels within 2 min, we hypothesize that the later, slow phase of relaxation (lasting up to 45 min) was due to a slow inactivation of nonphosphorylated cross bridges. Removing extracellular Ca2+ (0 mM CaCl2, 0.1 mM ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid) greatly enhanced the rate of the slow phase of relaxation, and raising extracellular CaCl2 to 5 mM slowed relaxation significantly. A slow rate of Ca2+ removal to a final concentration that maintains resting tone appears to produce the slow phase of relaxation. These results support hypotheses based on other studies of contracting muscles. There appear to be two populations of cross bridges interacting with the thin filament: 1) phosphorylated and capable of rapid cycling, and 2) dephosphorylated cross bridges that can maintain stress. The latter reflect an unidentified regulatory mechanism, which appears to have a high sensitivity for Ca2+.

scholarly journals Chromous ion reduction of mammalian cytochrome oxidase and some of its derivatives

1977 ◽  
Vol 165 (2) ◽  
pp. 413-416 ◽  
Author(s):  
C Greenwood ◽  
T Brittain ◽  
M Brunori ◽  
M T Wilson
Keyword(s):  
Mixed Valence ◽  
Slow Phase ◽  
High Concentration ◽  
Difference Spectra ◽  
Rapid Phase ◽  
Fast Phase ◽  
Two Phases ◽  
Rate Limit ◽  
Kinetics Of ◽  
Inhibited Enzyme

The reduction of cytochrome c oxidase by Cr2+, followed by means of stopped-flow spectrophotometry, exhibits two phases: the faster Cr2+-concentration-dependent reaction has an initial rate constant of 1.1 × 10(4)M-1-S-1, but reaches a rate limit at high concentration of reductant; the slower phase is concentration-independent with a rate of 0.3S-1. The activation energies of the fast and the slow processes are 35 and 71 kJ/mol respectively. The reduction kinetics of the mixed-valence CO complex and the cyanide-inhibited enzyme were compared with those of the fully oxidized forms: both the liganded species have a fast phase identical with that found in the oxidized oxidase. A comparison of the kinetic difference spectra obtained for the fast phase of reduction of oxidized oxidase with those obtained on reduction of the liganded species suggests that the rapid phase arises from the reduction ofhaem a, and the slow phase from the reduction of haem a3.

scholarly journals Two Phases of Actin Polymerization Display Different Dependencies on PI(3,4,5)P3 Accumulation and Have Unique Roles during Chemotaxis

2003 ◽  
Vol 14 (12) ◽  
pp. 5028-5037 ◽  
Author(s):  
Lingfeng Chen ◽  
Chris Janetopoulos ◽  
Yi Elaine Huang ◽  
Miho Iijima ◽  
Jane Borleis ◽  
...  
Keyword(s):  
Actin Polymerization ◽  
Slow Phase ◽  
Wild Type ◽  
Rapid Phase ◽  
Pi3k Inhibitors ◽  
Pi3k Inhibition ◽  
Directional Movement ◽  
Temporal And Spatial ◽  
Two Phases ◽  
Highly Correlated

The directional movement of cells in chemoattractant gradients requires sophisticated control of the actin cytoskeleton. Uniform exposure of Dictyostelium discoideum amoebae as well as mammalian leukocytes to chemoattractant triggers two phases of actin polymerization. In the initial rapid phase, motility stops and the cell rounds up. During the second slow phase, pseudopodia are extended from local regions of the cell perimeter. These responses are highly correlated with temporal and spatial accumulations of PI(3,4,5)P3/PI(3,4)P2 reflected by the translocation of specific PH domains to the membrane. The slower phase of PI accumulation and actin polymerization is more prominent in less differentiated, unpolarized cells, is selectively increased by disruption of PTEN, and is relatively more sensitive to perturbations of PI3K. Optimal levels of the second responses allow the cell to respond rapidly to switches in gradient direction by extending lateral pseudopods. Consequently, PI3K inhibitors impair chemotaxis in wild-type cells but partially restore polarity and chemotactic response in pten- cells. Surprisingly, the fast phase of PI(3,4,5)P3 accumulation and actin polymerization, which is relatively resistant to PI3K inhibition, can support inefficient but reasonably accurate chemotaxis.

scholarly journals The effect of experimental hematoma on serum levels of fibrinogen- related antigen

Blood ◽  
1976 ◽  
Vol 47 (5) ◽  
pp. 855-859
Author(s):  
J Cade ◽  
E Regoeczi ◽  
J Hirsh ◽  
M Buchanan
Keyword(s):  
Time Course ◽  
Serum Levels ◽  
Slow Phase ◽  
Homologous Blood ◽  
Rapid Phase ◽  
Baseline Levels ◽  
Total Body ◽  
Circulating Levels

The effect of experimental hematomas on serum levels of fibrinogen- related antigen (FRA) was studied in rabbits. Homologous blood used for production of hematomas was mixed with 131I-fibrinogen, and the measurement of FRA was made using a radioactive technique (representing FRA from hematoma) and immunologically (representing total FRA). Total body radiation of animals bearing hematomas containing 131I-fibrinogen decayed slowly (mean t 1/2 = 189 hr) over the first 2–3 days and then rapidly (mean t 1/2 = 43 hr) during the subsequent days. Serum FRA levels measured immunologically rose transiently from 4 to 11 mug/ml during the slow phase of hematoma resolution, and returned to baseline levels during the rapid phase of resolution. The appearance of a small amount of protein-bound radioactivity in the blood of animals with hematomas paralleled the time course of the changes in immunologically determined FRA, but, even at its peak, circulating levels only averaged 0.36% of the administered tracer. From these observations, it seemed unlikely that the dissolution of fibrin which may form as the result of bleeding into tissues would significatnly contribute to levels of circulating FRA.

scholarly journals The effect of experimental hematoma on serum levels of fibrinogen- related antigen

Blood ◽  
1976 ◽  
Vol 47 (5) ◽  
pp. 855-859 ◽  
Author(s):  
J Cade ◽  
E Regoeczi ◽  
J Hirsh ◽  
M Buchanan
Keyword(s):  
Time Course ◽  
Serum Levels ◽  
Slow Phase ◽  
Homologous Blood ◽  
Rapid Phase ◽  
Baseline Levels ◽  
Total Body ◽  
Circulating Levels

Abstract The effect of experimental hematomas on serum levels of fibrinogen- related antigen (FRA) was studied in rabbits. Homologous blood used for production of hematomas was mixed with 131I-fibrinogen, and the measurement of FRA was made using a radioactive technique (representing FRA from hematoma) and immunologically (representing total FRA). Total body radiation of animals bearing hematomas containing 131I-fibrinogen decayed slowly (mean t 1/2 = 189 hr) over the first 2–3 days and then rapidly (mean t 1/2 = 43 hr) during the subsequent days. Serum FRA levels measured immunologically rose transiently from 4 to 11 mug/ml during the slow phase of hematoma resolution, and returned to baseline levels during the rapid phase of resolution. The appearance of a small amount of protein-bound radioactivity in the blood of animals with hematomas paralleled the time course of the changes in immunologically determined FRA, but, even at its peak, circulating levels only averaged 0.36% of the administered tracer. From these observations, it seemed unlikely that the dissolution of fibrin which may form as the result of bleeding into tissues would significatnly contribute to levels of circulating FRA.

Aluminium Uptake by Excised Roots of Cabbage, Lettuce and Kikuyu Grass

1979 ◽  
Vol 6 (6) ◽  
pp. 643 ◽  
Author(s):  
DO Huett ◽  
RC Menary
Keyword(s):  
Time Course ◽  
Cation Exchange Resin ◽  
Effect Of Temperature ◽  
Metabolic Inhibitor ◽  
Rapid Phase ◽  
Uptake Process ◽  
Accumulation Phase ◽  
Kikuyu Grass ◽  
Two Phases

Uptake of aluminium by excised roots of cabbage, lettuce, kikuyu grass and by a weakly acidic cation exchange resin was studied. The role of metabolism was also investigated, using a range of temperatures and a metabolic inhibitor. The time course of uptake had two phases: an initial rapid phase of about 60 min duration for all species and a slower accumulation phase that was pronounced for cabbage and lettuce and almost absent for kikuyu grass. During the initial phase, calcium was exchanged by aluminium. A small fraction of the aluminium taken up by excised roots could not be desorbed by dilute buffer; this was thought to result from irreversible binding of aluminium directly to exchange sites. Evidence is also presented for a third component for aluminium uptake involving diffusion through the plasmalemma. The non-metabolic nature of the entire uptake process was confirmed by the negligible effect of temperature (1-30°C) and enhancement by 2,4-dinitrophenol on the rate of uptake. Aluminium uptake at pH 4.2 exceeded that at pH 4.0, probably due to the lowering of net charge density of aluminium ions as pH is increased.

Gastrulation in Drosophila: the formation of the ventral furrow and posterior midgut invaginations

Development ◽  
1991 ◽  
Vol 112 (3) ◽  
pp. 775-789 ◽  
Author(s):  
D. Sweeton ◽  
S. Parks ◽  
M. Costa ◽  
E. Wieschaus
Keyword(s):  
Cell Shape ◽  
Time Course ◽  
Drosophila Embryo ◽  
Second Phase ◽  
Rapid Phase ◽  
Apical Constriction ◽  
Posterior Midgut ◽  
Ventral Furrow ◽  
Two Phases ◽  
Shape Changes

The ventral furrow and posterior midgut invaginations bring mesodermal and endodermal precursor cells into the interior of the Drosophila embryo during gastrulation. Both invaginations proceed through a similar sequence of rapid cell shape changes, which include apical flattening, constriction of the apical diameter, cell elongation and subsequent shortening. Based on the time course of apical constriction in the ventral furrow and posterior midgut, we identify two phases in this process: first, a slow stochastic phase in which some individual cells begin to constrict and, second, a rapid phase in which the remaining unconstricted cells constrict. Mutations in the concertina or folded gastrulation genes appear to block the transition to the second phase in both the ventral furrow and the posterior midgut invaginations.

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