scholarly journals Metabolic constraints on the recovery of sensitivity after visual pigment bleaching in retinal rods

2009 ◽  
Vol 134 (3) ◽  
pp. 165-175 ◽  
Author(s):  
Kiyoharu J. Miyagishima ◽  
M. Carter Cornwall ◽  
Alapakkam P. Sampath
Keyword(s):  
Time Constant ◽  
Visual Pigment ◽  
Outer Segment ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Bright Light ◽  
Primary Source ◽  
Retinal Rods ◽  
Before And After ◽  
Active Intermediates ◽  
Phototransduction Cascade

The shutoff of active intermediates in the phototransduction cascade and the reconstitution of the visual pigment play key roles in the recovery of sensitivity after the exposure to bright light in both rod and cone photoreceptors. Physiological evidence from bleached salamander rods suggests this recovery of sensitivity occurs faster at the outer segment base compared with the tip. Microfluorometric measurements of similarly bleached salamander rods demonstrate that the reduction of all-trans retinal to all-trans retinol also occurs more rapidly at the outer segment base than at the tip. The experiments reported here were designed to test the hypothesis that these two phenomena are linked, e.g., that slowed recovery of sensitivity at the tip of outer segments is rate limited by the reduction of all-trans retinal and results from a shortage of cytosolic nicotinamide adenine dinucleotide phosphate (NADPH), the reducing agent for all-trans retinal reduction. Extracellular measurements of membrane current and sensitivity were made from isolated salamander rods under dark-adapted and bleached conditions while intracellular NADPH concentration was varied by dialysis from a micropipette attached to the inner segment. Sensitivity at the base and tip of the outer segment was assessed before and after bleaching. After exposure to a light that photoactivates 50% of the visual pigment, rods were completely insensitive for nearly 10 minutes, after which the base recovered sensitivity and responsiveness with a time constant of ∼200 seconds, but tip sensitivity recovered more slowly with a time constant of ∼680 seconds. Dialysis of 5 mM NADPH into the rod promoted an earlier recovery and eliminated the previously observed tip/base difference. Dialysis of 1.66 mM NADPH failed to eliminate the tip/base recovery difference, suggesting the steady-state NADPH concentration in rods is ∼1 mM. These results indicate the inner segment is the primary source of reducing equivalents after pigment bleaching, with the reduction of all-trans retinal to all-trans retinol playing a key step in the recovery of sensitivity.

scholarly journals Origin and control of the dominant time constant of salamander cone photoreceptors

2012 ◽  
Vol 140 (2) ◽  
pp. 219-233 ◽  
Author(s):  
Jingjing Zang ◽  
Hugh R. Matthews
Keyword(s):  
Time Constant ◽  
External Solution ◽  
Light Response ◽  
Response Recovery ◽  
Bright Flash ◽  
Active Intermediates ◽  
And Control ◽  
Flash Response ◽  
Phototransduction Cascade ◽  
External Ph

Recovery of the light response in vertebrate photoreceptors requires the shutoff of both active intermediates in the phototransduction cascade: the visual pigment and the transducin–phosphodiesterase complex. Whichever intermediate quenches more slowly will dominate photoresponse recovery. In suction pipette recordings from isolated salamander ultraviolet- and blue-sensitive cones, response recovery was delayed, and the dominant time constant slowed when internal [Ca2+] was prevented from changing after a bright flash by exposure to 0Ca2+/0Na+ solution. Taken together with a similar prior observation in salamander red-sensitive cones, these observations indicate that the dominance of response recovery by a Ca2+-sensitive process is a general feature of amphibian cone phototransduction. Moreover, changes in the external pH also influenced the dominant time constant of red-sensitive cones even when changes in internal [Ca2+] were prevented. Because the cone photopigment is, uniquely, exposed to the external solution, this may represent a direct effect of protons on the equilibrium between its inactive Meta I and active Meta II forms, consistent with the notion that the process dominating recovery of the bright flash response represents quenching of the active Meta II form of the cone photopigment.

Effect of hydroxylamine on the subcellular distribution of arrestin (S-antigen) in rod photoreceptors

1994 ◽  
Vol 11 (3) ◽  
pp. 561-568 ◽  
Author(s):  
Nancy J. Mangini ◽  
Grady L. Garner ◽  
Tinging L. Okajima ◽  
Larry A. Donoso ◽  
David R. Pepperberg
Keyword(s):  
Visual Pigment ◽  
Driving Force ◽  
Outer Segment ◽  
Processing System ◽  
Bright Light ◽  
Photoreceptor Outer Segment ◽  
Rod Photoreceptors ◽  
Average Value ◽  
Secondary Antibodies ◽  
Microscopic Image Processing

AbstractThe immunocytochemical labeling of arrestin (S-antigen) in photoreceptors of the ovine retina was examined following incubation of the retina with hydroxylamine (NH2OH), an agent known to inhibit the phosphorylation of photoactivated rhodopsin. Intact, isolated retinas bathed in medium containing 20 mM NH2OH, or in control medium lacking NH2OH, were maintained in darkness or exposed to bright light for 3 min (dark-adapted and light-adapted conditions, respectively); further incubated in darkness for 10 min; and then fixed and prepared for cryosectioning. Cryosections were incubated with anti-S-antigen monoclonal antibody MAb A2G5; with secondary antibodies that were conjugated with horseradish peroxidase; and with either 3–amino-9–ethyl carbazole or diaminobenzidine as chromogen. Anti-arrestin labeling in cryosections was then analyzed densitometrically using a light-microscopic image processing system. In dark-adapted control retinas, labeling density of the photoreceptor outer segment (OS) layer (0.061 ± 0.004; average ± S.e.m.) was less than that of the inner segment (IS) layer (0.138 ± 0.011). In light-adapted control retinas, OS labeling density (0.139 ± 0.007) exceeded IS labeling density (0.095 ± 0.005). Incubation with NH2OH eliminated this light-dependent increase in labeling of the OS relative to that of the IS, i.e. eliminated the increase in relative OS/IS labeling. Densities of labeling were 0.110 ± 0.006 (OS) and 0.183 ± 0.006 (IS) in NH2OH-treated dark-adapted retinas vs. 0.078 ± 0.004 (OS) and 0.182 ± 0.008 (IS) in NH2OH-treated light-adapted retinas. Anti-arrestin labeling was also examined in retinas that were exposed to 3 min or 13 min of bright light and then immediately fixed. Among retinas incubated in the absence of NH2OH, an increase in OS/IS labeling density was evident after 3 min of illumination, and retinas illuminated for 13 min exhibited an even larger increase in OS/IS labeling. An increase in OS/IS labeling was also exhibited by NH2OH-treated retinas that had been illuminated for 3 min; by comparison with dark-adapted NH2OH-treated controls (average value of OS/IS labeling: 0.60), OS/IS labeling in these illuminated retinas was 0.97. However, OS/IS labeling in NH2OH-treated retinas that had been illuminated for 13 min (average value: 0.35) was lower than that of the dark-adapted controls. The results indicate that, within intact rods, NH2OH inhibits the light-dependent increase in OS/IS anti-arrestin labeling that is ordinarily expressed at long times (~10 min) after major bleaching of the visual pigment. Among the possible bases for the effect of NH2OH are a reduction in the driving force for the movement of arrestin from the inner to the outer segment and/or a facilitation of the degradation of arrestin in the outer segment.

scholarly journals Cellular mechanisms that underlie bleaching and background adaptation.

1990 ◽  
Vol 96 (2) ◽  
pp. 345-372 ◽  
Author(s):  
M C Cornwall ◽  
A Fein ◽  
E F MacNichol
Keyword(s):  
Steady State ◽  
Visual Pigment ◽  
Outer Segment ◽  
Tiger Salamander ◽  
Cellular Mechanisms ◽  
Rod Photoreceptors ◽  
Background Adaptation ◽  
Before And After ◽  
Space Constant ◽  
Local Test

Experiments were performed on rod photoreceptors isolated from the eye of the larval tiger salamander to determine if the same or different mechanisms underlie the desensitization produced by dim background light (background adaptation) and that which persists in the steady state in darkness after a significant fraction of the photopigment is bleached (bleaching adaptation). We have examined adaptational effects after light that bleached between approximately 50% and 95% of the photopigment under conditions which preclude pigment regeneration. The steady-state desensitization, far greater than that predicted by quantum-catch loss, is relieved upon regeneration of the visual pigment with 11-cis retinal. We measured the spread of desensitization along the long axis of the rod after a local bright bleach at one end by comparing responses to dim local test flashes elicited in different regions of the outer segment, before and after bleaching. The space constant for this spread was less than 2.5 microns. We have previously measured the space constant for the longitudinal spread of desensitization during a local dim background in Ambystoma rods to be 7 microns. This is similar to a space constant of 6 microns measured under similar conditions in Bufo rods by Lamb et al. (1981. J. Physiol. 319:463-496). If calcium carries the signal for background desensitization, this difference in space constant for background and bleaching adaptation precludes it as the messenger for the steady component of bleaching adaptation. Experiments with isobutylmethyl xanthine (IBMX) also indicate that Ca2+ as well as c-GMP are unlikely regulators of bleaching desensitization, since elevation of cytosolic levels of both of these internal messengers by IBMX has little effect on sensitivity in bleach-adapted cells. All of our findings are consistent with the notion that bleaching adaptation is not mediated by a freely diffusible cytoplasmic messenger.

Freeze-Fracture Replication of Frozen Outer Segments of Rat Retinal Rods

1969 ◽  
Vol 27 ◽  
pp. 392-393
Author(s):  
Thomas S. Leeson ◽  
C. Roland Leeson
Keyword(s):  
Electron Microscopy ◽  
Cross Section ◽  
Outer Segment ◽  
Freeze Fracture ◽  
X Ray Diffraction ◽  
X Ray ◽  
Outer Segments ◽  
Retinal Rods ◽  
Temperature Electron ◽  
Freeze Etching

Numerous previous studies of outer segments of retinal receptors have demonstrated a complex internal structure of a series of transversely orientated membranous lamellae, discs, or saccules. In cones, these lamellae probably are invaginations of the covering plasma membrane. In rods, however, they appear to be isolated and separate discs although some authors report interconnections and some continuities with the surface near the base of the outer segment, i.e. toward the inner segment. In some species, variations have been reported, such as longitudinally orientated lamellae and lamellar whorls. In cross section, the discs or saccules show one or more incisures. The saccules probably contain photolabile pigment, with resulting potentials after dipole formation during bleaching of pigment. Continuity between the lamina of rod saccules and extracellular space may be necessary for the detection of dipoles, although such continuity usually is not found by electron microscopy. Particles on the membranes have been found by low angle X-ray diffraction, by low temperature electron microscopy and by freeze-etching techniques.

Nilai-Nilai Pendidikan Akhlak dalam Al-Qur’an

2018 ◽  
Vol 10 (2) ◽  
pp. 269-295
Author(s):  
Sri Waluyo
Keyword(s):  
Moral Education ◽  
Primary Source ◽  
Secondary Data ◽  
Primary Data ◽  
The Core ◽  
Primary Data Source ◽  
Before And After ◽  
Data Source

This paper discusses the content of Q.S. al-Baqarah ([2]: 67-73). The data used in the preparation of this paper is the data that is primary and secondary. The primary source is data obtained from the core source. In conducting a study of a verse, it is clear that the primary data source is derived from the Qur'an,precisely on Q.S. al-Baqarah ([2]: 67-73). Secondary data is dataobtained from other sources that are still related to the problemand provide interpretation of the primary source. The method usedin analyzing this paper is the tahlili method. This method describesthe meaning contained by the Qur'an, verse by verse, and letterafter letter according to the order in the Mushaf. The descriptionincludes the various aspects which the interpreted verses contain,such as the meaning of the vocabulary, the connotation of thesentence, the background of the verse down, its relation to otherverses, both before and after. And do not miss the opinion that hasbeen given regarding the interpretation of these verses, whetherdelivered by the Prophet, companions, the tabi'in, as well as othercommentators. This study shows that in Q.S. (2): 67-73) there arevalues of moral education which include: 1) morals in asking, (2)morals to parents, (3) patience of educators, (4) educator honesty,and (5) obedience of learners.

scholarly journals Diffusion of calcium ions in retinal rods. A theoretical calculation.

1981 ◽  
Vol 77 (4) ◽  
pp. 475-487 ◽  
Author(s):  
S McLaughlin ◽  
J Brown
Keyword(s):  
Diffusion Coefficient ◽  
Adsorption Isotherm ◽  
Calcium Ions ◽  
Outer Segment ◽  
Effective Diffusion ◽  
Langmuir Adsorption Isotherm ◽  
Diffuse Double Layer ◽  
Langmuir Adsorption ◽  
Retinal Rods ◽  
Disk Membrane

The Fick diffusion equation is combined with the Langmuir adsorption isotherm and the relevant equations from the Gouy-Chapman theory of the electrical diffuse double layer to demonstrate that the effective diffusion coefficient of calcium ions, both in the cytoplasm of the rod outer segment and within the aqueous space bounded by the disk membrane, should be reduced by a factor of 10-100 because these ions adsorb to phospholipids present in the disk membrane.

scholarly journals Light-dependent binding of G-protein to outer segment membranes of toad photoreceptors.

1986 ◽  
Vol 88 (5) ◽  
pp. 675-694 ◽  
Author(s):  
N J Mangini ◽  
D R Pepperberg ◽  
W Baehr
Keyword(s):  
G Protein ◽  
Visual Pigment ◽  
Outer Segment ◽  
Tight Binding ◽  
Beta Subunits ◽  
Hypotonic Medium ◽  
Intense Light ◽  
Low Levels ◽  
Toad Bufo ◽  
Peak Value

Light-dependent changes in the binding of G-protein were analyzed in outer segment disk membranes obtained from photoreceptors of the toad (Bufo marinus) retina. Isolated, intact retinas, incubated in oxygenated Ringer's solution at 23 +/- 1 degree C, were subjected to various conditions of illumination and then incubated in darkness for specified periods. The retinas were then chilled (0-4 degrees C) and the receptor outer segments (ROS) were isolated. Binding of the alpha- and beta-subunits of G-protein to the ROS membranes was analyzed by quantitating G alpha and G beta extracted from the membranes with hypotonic medium lacking GTP vs. hypotonic medium containing GTP (H and HG extracts, respectively). For retinas illuminated and then immediately chilled for analysis, the extent of G binding (relative abundance of G alpha, beta in the HG extract) increased with the extent of bleaching of the visual pigment. Near-maximal binding was observed after bleaches of greater than or equal to 30%. With an increasing period of incubation in darkness after approximately 70% bleaching, the extent of binding declined gradually to low levels characteristic of unbleached retinas. The period required for half-completion of the decline was approximately 10(3) s. A gradual decline in G binding, from a rapidly developing peak value, was also observed with an increasing period of exposure to intense light. Viewed in the context of previous electrophysiological data, our results indicate that sustained bleaching desensitization of the rods does not depend upon a persisting state of "tight binding" (immobilization) of G-protein by bleached visual pigment.

Effects of methacholine and hypocapnia on airways and collateral ventilation in dogs

1979 ◽  
Vol 46 (5) ◽  
pp. 966-972 ◽  
Author(s):  
L. J. Smith ◽  
C. R. Inners ◽  
P. B. Terry ◽  
H. A. Menkes ◽  
R. J. Traystman
Keyword(s):  
Time Constant ◽  
Fiber Optic ◽  
Small Airways ◽  
Before And After ◽  
Airways Resistance ◽  
Lung Deflation ◽  
Collateral Ventilation

We studied the effects of hypocapnia and methacholine on small airways resistance (Rsaw) and collateral ventilation in anesthetized paralyzed dogs. The animals were ventilated with air while either 10% CO2 or air (hypocapnia) was infused through a segment obstructed with a fiber-optic bronchoscope. Measurements were made before and after instillation of methacholine into the obstructed segment. Collateral resistance (Rcoll) and Rsaw increased with hypocapnia and methacholine. The time constant for collateral ventilation increased with hypocapnia, but did not change with methacholine because of decreases in the compliance of the obstructed segment. We conclude that collateral channels respond to methacholine and hypocapnia in a manner similar to small airways and that local parasympathomimetic stimulation, unlike lung deflation does not increase the time constant for collateral ventilation.

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