Adaptation in Vertebrate Photoreceptors

2001 ◽  
Vol 81 (1) ◽  
pp. 117-151 ◽  
Author(s):  
Gordon L. Fain ◽  
Hugh R. Matthews ◽  
M. Carter Cornwall ◽  
Yiannis Koutalos
Keyword(s):  
G Protein ◽  
Outer Segment ◽  
Light Adaptation ◽  
Electrical Response ◽  
Light Level ◽  
Free Concentration ◽  
Background Adaptation ◽  
Vertebrate Photoreceptor ◽  
Intracellular Ca ◽  
The One

When light is absorbed within the outer segment of a vertebrate photoreceptor, the conformation of the photopigment rhodopsin is altered to produce an activated photoproduct called metarhodopsin II or Rh*. Rh* initiates a transduction cascade similar to that for metabotropic synaptic receptors and many hormones; the Rh*activates a heterotrimeric G protein, which in turn stimulates an effector enzyme, a cyclic nucleotide phosphodiesterase. The phosphodiesterase then hydrolyzes cGMP, and the decrease in the concentration of free cGMP reduces the probability of opening of channels in the outer segment plasma membrane, producing the electrical response of the cell. Photoreceptor transduction can be modulated by changes in the mean light level. This process, called light adaptation (or background adaptation), maintains the working range of the transduction cascade within a physiologically useful region of light intensities. There is increasing evidence that the second messenger responsible for the modulation of the transduction cascade during background adaptation is primarily, if not exclusively, Ca2+, whose intracellular free concentration is decreased by illumination. The change in free Ca2+ is believed to have a variety of effects on the transduction mechanism, including modulation of the rate of the guanylyl cyclase and rhodopsin kinase, alteration of the gain of the transduction cascade, and regulation of the affinity of the outer segment channels for cGMP. The sensitivity of the photoreceptor is also reduced by previous exposure to light bright enough to bleach a substantial fraction of the photopigment in the outer segment. This form of desensitization, called bleaching adaptation (the recovery from which is known as dark adaptation), seems largely to be due to an activation of the transduction cascade by some form of bleached pigment. The bleached pigment appears to activate the G protein transducin directly, although with a gain less than Rh*. The resulting decrease in intracellular Ca2+ then modulates the transduction cascade, by a mechanism very similar to the one responsible for altering sensitivity during background adaptation.

scholarly journals Rhodopsin kinase and recoverin modulate phosphodiesterase during mouse photoreceptor light adaptation

2015 ◽  
Vol 145 (3) ◽  
pp. 213-224 ◽  
Author(s):  
Ching-Kang Chen ◽  
Michael L. Woodruff ◽  
Gordon L. Fain
Keyword(s):  
G Protein ◽  
Outer Segment ◽  
Light Adaptation ◽  
Prolonged Exposure ◽  
Genetic Manipulation ◽  
Electrical Response ◽  
Light Response ◽  
Background Light ◽  
Rhodopsin Kinase ◽  
Pde Inhibition

Light stimulates rhodopsin in a retinal rod to activate the G protein transducin, which binds to phosphodiesterase (PDE), relieving PDE inhibition and decreasing guanosine 3′,5′-cyclic monophosphate (cGMP) concentration. The decrease in cGMP closes outer segment channels, producing the rod electrical response. Prolonged exposure to light decreases sensitivity and accelerates response kinetics in a process known as light adaptation, mediated at least in part by a decrease in outer segment Ca2+. Recent evidence indicates that one of the mechanisms of adaptation in mammalian rods is down-regulation of PDE. To investigate the effect of light and a possible role of rhodopsin kinase (G protein–coupled receptor kinase 1 [GRK1]) and the GRK1-regulating protein recoverin on PDE modulation, we used transgenic mice with decreased expression of GTPase-accelerating proteins (GAPs) and, consequently, a less rapid decay of the light response. This slowed decay made the effects of genetic manipulation of GRK1 and recoverin easier to observe and interpret. We monitored the decay of the light response and of light-activated PDE by measuring the exponential response decay time (τREC) and the limiting time constant (τD), the latter of which directly reflects light-activated PDE decay under the conditions of our experiments. We found that, in GAP-underexpressing rods, steady background light decreased both τREC and τD, and the decrease in τD was nearly linear with the decrease in amplitude of the outer segment current. Background light had little effect on τREC or τD if the gene for recoverin was deleted. Moreover, in GAP-underexpressing rods, increased GRK1 expression or deletion of recoverin produced large and highly significant accelerations of τREC and τD. The simplest explanation of our results is that Ca2+-dependent regulation of GRK1 by recoverin modulates the decay of light-activated PDE, and that this modulation is responsible for acceleration of response decay and the increase in temporal resolution of rods in background light.

scholarly journals Phosducin Regulates the Expression of Transducin βγ Subunits in Rod Photoreceptors and Does Not Contribute to Phototransduction Adaptation

2007 ◽  
Vol 130 (3) ◽  
pp. 303-312 ◽  
Author(s):  
Claudia M. Krispel ◽  
Maxim Sokolov ◽  
Yen-Ming Chen ◽  
Hongman Song ◽  
Rolf Herrmann ◽  
...  
Keyword(s):  
G Protein ◽  
Outer Segment ◽  
Light Adaptation ◽  
Wild Type ◽  
Rod Photoreceptors ◽  
Response Properties ◽  
Adaptation Mechanisms ◽  
Subunit Expression

For over a decade, phosducin's interaction with the βγ subunits of the G protein, transducin, has been thought to contribute to light adaptation by dynamically controlling the amount of transducin heterotrimer available for activation by photoexcited rhodopsin. In this study we directly tested this hypothesis by characterizing the dark- and light-adapted response properties of phosducin knockout (Pd−/−) rods. Pd−/− rods were notably less sensitive to light than wild-type (WT) rods. The gain of transduction, as measured by the amplification constant using the Lamb-Pugh model of activation, was 32% lower in Pd−/− rods than in WT rods. This reduced amplification correlated with a 36% reduction in the level of transducin βγ-subunit expression, and thus available heterotrimer in Pd−/− rods. However, commonly studied forms of light adaptation were normal in the absence of phosducin. Thus, phosducin does not appear to contribute to adaptation mechanisms of the outer segment by dynamically controlling heterotrimer availability, but rather is necessary for maintaining normal transducin expression and therefore normal flash sensitivity in rods.

The photoreceptor cytoskeleton visualized

1992 ◽  
Vol 50 (1) ◽  
pp. 480-481
Author(s):  
Beth Burnside
Keyword(s):  
Outer Segment ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Cell Polarization ◽  
Synaptic Proteins ◽  
Cell Functions ◽  
Vertebrate Photoreceptor ◽  
Numerous Cell ◽  
Turn Over

The vertebrate photoreceptor provides a drammatic example of cell polarization. Specialized to carry out phototransduction at its distal end and to synapse with retinal interneurons at its proximal end, this long slender cell has a uniquely polarized morphology which is reflected in a similarly polarized cytoskeleton. Membranes bearing photopigment are localized in the outer segment, a modified sensory cilium. Sodium pumps which maintain the dark current critical to photosensory transduction are anchored along the inner segment plasma membrane between the outer segment and the nucleus.Proximal to the nucleus is a slender axon terminating in specialized invaginating synapses with other neurons of the retina. Though photoreceptor diameter is only 3-8u, its length from the tip of the outer segment to the synapse may be as great as 200μ. This peculiar linear cell morphology poses special logistical problems and has evoked interesting solutions for numerous cell functions. For example, the outer segment membranes turn over by means of a unique mechanism in which new disks are continuously added at the proximal base of the outer segment, while effete disks are discarded at the tip and phagocytosed by the retinal pigment epithelium. Outer segment proteins are synthesized in the Golgi near the nucleus and must be transported north through the inner segment to their sites of assembly into the outer segment, while synaptic proteins must be transported south through the axon to the synapse.The role of the cytoskeleton in photoreceptor motile processes is being intensely investigated in several laboratories.

Disturbing Gtp-Binding Protein Function Through Microinjection Into The Visual Cell Of Limulus

1992 ◽  
Vol 47 (11-12) ◽  
pp. 915-921 ◽  
Author(s):  
Henmg Stieve ◽  
Barbara Niemeyer ◽  
Klaus Aktories ◽  
Heidi E. Hamm
Keyword(s):  
Monoclonal Antibody ◽  
G Protein ◽  
Protein Function ◽  
Clostridium Botulinum ◽  
Functional Role ◽  
Electrical Response ◽  
Visual Cell ◽  
Gtp Binding ◽  
Dim Light ◽  
Ventral Nerve Photoreceptor

We have tested the action of three agents microinjected into the ventral nerve photoreceptor of Limulus on the electrical response to dim light. 1. A monoclonal antibody (mAb 4 A) against the Gɑ subunit of frog transducin reduces the size of the receptor current to 60%, suggesting an interaction with Gɑ in the Limulus photoreceptor. 2. Injection of Clostridium botulinum ADPribosyltransferase C 3 reduces the size to 46%; latency is not affected. The results imply that small GTP-binding proteins play a functional role in photoreception of invertebrates. 3. Injection of GD P-β-S reduces dose-dependently the size of the receptor current to 15% and prolongs the latency to 200%, presumably by reducing number and rate of G-protein activations

scholarly journals Norepinephrine exocytosis stimulated by α–latrotoxin requires both external and stored Ca 2+ and is mediated by latrophilin, G proteins and phospholipase C

1999 ◽  
Vol 354 (1381) ◽  
pp. 379-386 ◽  
Author(s):  
M. Atiqur Rahman ◽  
Anthony C. Ashton ◽  
Frédéric A. Meunier ◽  
Bazbek A. Davletov ◽  
J. Oliver Dolly ◽  
...  
Keyword(s):  
Phospholipase C ◽  
G Protein ◽  
G Proteins ◽  
Fluorescent Dyes ◽  
Transmembrane Protein ◽  
Clostridial Neurotoxins ◽  
Dependent Component ◽  
Intracellular Ca ◽  
Botulinum Neurotoxins ◽  
Vesicular Exocytosis

α–latrotoxin (LTX) stimulates massive release of neurotransmitters by binding to a heptahelical transmembrane protein, latrophilin. Our experiments demonstrate that latrophilin is a G–protein–coupled receptor that specifically associates with heterotrimeric G proteins. The latrophilin–G protein complex is very stable in the presence of GDP but dissociates when incubated with GTP, suggesting a functional interaction. As revealed by immunostaining, latrophilin interacts with Gα q/11 and Gα o but not with Gα s , Gα i or Gα z , indicating that this receptor may couple to several G proteins but it is not promiscuous. The mechanisms underlying LTX–evoked norepinephrine secretion from rat brain nerve terminals were also studied. In the presence of extracellular Ca 2+ , LTX triggers vesicular exocytosis because botulinum neurotoxins E, C1 or tetanus toxin inhibit the Ca 2+ –dependent component of the toxin–evoked release. Based on (i) the known involvement of Gα q in the regulation of inositol–1,4,5–triphosphate generation and (ii) the requirement of Ca 2+ in LTX action, we tested the effect of inhibitors of Ca 2+ mobilization on the toxin–evoked norepinephrine release. It was found that aminosteroid U73122, which inhibits the coupling of G proteins to phospholipase C, blocks the Ca 2+ –dependent toxin's action. Thapsigargin, which depletes intracellular Ca 2+ stores, also potently decreases the effect of LTX in the presence of extracellular Ca 2+ . On the other hand, clostridial neurotoxins or drugs interfering with Ca 2+ metabolism do not inhibit the Ca 2+ –independent component of LTX–stimulated release. In the absence of Ca 2+ , the toxin induces in the presynaptic membrane non–selective pores permeable to small fluorescent dyes; these pores may allow efflux of neurotransmitters from the cytoplasm. Our results suggest that LTX stimulates norepinephrine exocytosis only in the presence of external Ca 2+ provided intracellular Ca 2+ stores are unperturbed and that latrophilin, G proteins and phospholipase C may mediate the mobilization of stored Ca 2+ , which then triggers secretion.

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.

Light adaptation and color opponency of horizontal cells in the turtle retina

2003 ◽  
Vol 20 (4) ◽  
pp. 437-452 ◽  
Author(s):  
GILAD TWIG ◽  
HANNA LEVY ◽  
ELITE WEINER ◽  
IDO PERLMAN
Keyword(s):  
Light Adaptation ◽  
Light Sensitivity ◽  
Horizontal Cells ◽  
Background Illumination ◽  
Voltage Range ◽  
Background Adaptation ◽  
Color Opponency ◽  
Light Stimuli ◽  
Type C

Chromaticity-type (C-type) horizontal cells of the turtle retina receive antagonistic inputs from cones of different spectral types, and therefore their response to background illumination is expected to reflect light adaptation of the cones and the interactions between their antagonistic inputs. Our goal was to study the behavior of C-type horizontal cells during background illumination and to evaluate the role of wavelength in background adaptation. The photoresponses of C-type horizontal cells were recorded intracellularly in the everted eyecup preparation of the turtleMauremys caspicaduring chromatic background illuminations. The voltage range of operation was either reduced or augmented, depending upon the wavelengths of the background and of the light stimuli, while the sensitivity to light was decreased by any background. The response–intensity curves were shifted to brighter intensities and became steeper as the background lights were made brighter regardless of wavelength. Comparing the effects of cone iso-luminant backgrounds on the Red/Green C-type horizontal cells indicated that background desensitization in these cells could not solely reflect background adaptation of cones but also depend upon response compression/expansion and changes in synaptic transmission. This leads to wavelength dependency of background adaptation in C-type horizontal cells, that is expressed as increased light sensitivity (smaller threshold elevation) and improved suprathreshold contrast detection when the wavelengths of the background and light stimuli were chosen to exert opponent effects on membrane potential.

scholarly journals G-protein dependent dual modulation by adenosine of ATP-evoked inward currents and intracellular Ca increase in PC12 cells.

1993 ◽  
Vol 61 ◽  
pp. 131
Author(s):  
Kazuhide Inoue ◽  
Tomokazu Watano ◽  
Shuichi Koizumi ◽  
Geoffrey Burnstock
Keyword(s):  
G Protein ◽  
Pc12 Cells ◽  
Intracellular Ca ◽  
Inward Currents
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