scholarly journals Axial gradients of rhodopsin in light-exposed retinal rods of the toad.

1990 ◽  
Vol 96 (6) ◽  
pp. 1199-1220 ◽  
Author(s):  
C L Makino ◽  
L N Howard ◽  
T P Williams
Keyword(s):  
Mathematical Model ◽  
Outer Segment ◽  
Light Adaptation ◽  
Monochromatic Light ◽  
Spectral Content ◽  
Photoreceptor Outer Segments ◽  
Rod Outer Segment ◽  
Lighting Conditions ◽  
Retinal Rods ◽  
Vertebrate Eye

Exposure of an intact vertebrate eye to light bleaches the rhodopsin in the photoreceptor outer segments in spatially nonuniform patterns. Some axial bleaching patterns produced in toad rods were determined using microspectrophotometric techniques. More rhodopsin was bleached at the base of the outer segment than at the distal tip. The shape of the bleaching gradient varied with the extent of bleach and with the spectral content of the illuminant. Monochromatic light at the lambda max of the rhodopsin gave rise to the steepest bleaching gradients and induced the greatest changes in the form of the gradient with increasing extent of bleach. These results were consistent with a mathematical model for pigment bleaching in an unstirred sample. The model did not fit bleaching patterns resulting from special lighting conditions that promoted the photoregeneration of rhodopsin from the intermediates of bleaching. Prolonged light adaptation of toads could also produce axial rhodopsin gradients that were not fit by the bleaching model. Under certain conditions the axial gradient of rhodopsin in a rod outer segment reversed with time in the light: the rhodopsin content became highest at the base. This result could be explained by an interaction between the pattern of bleaching and the intracellular topography of regeneration.

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.

Movement of retinal along cone and rod photoreceptors

1994 ◽  
Vol 11 (2) ◽  
pp. 389-399 ◽  
Author(s):  
Jing Jin ◽  
Gregor J. Jones ◽  
M. Carter Cornwall
Keyword(s):  
Cell Body ◽  
Dark Adaptation ◽  
Visual Pigment ◽  
Outer Segment ◽  
Light Adaptation ◽  
Rod Photoreceptors ◽  
Rod Outer Segment ◽  
Rods And Cones ◽  
Outer Segments ◽  
Rod Cell

AbstractSingle isolated photoreceptors can be taken through a visual cycle of light adaptation by bleaching visual pigment, followed by dark adaptation when supplied with 11–cis retinal. Light adaptation after bleaching is manifested by faster response kinetics and a permanent reduction in sensitivity to light flashes, presumed to be due to the presence of bleached visual pigment. The recovery of flash sensitivity during dark adaptation is assumed to be due to regeneration of visual pigment to pre-bleach levels. In previous work, the outer segments of bleached, light-adapted cells were exposed to 11–cis retinal. In the present work, the cell bodies of bleached photoreceptors were exposed. We report a marked difference between rods and cones. Bleached cones recover sensitivity when their cell bodies are exposed to 11–cis retinal. Bleached rods do not. These results imply that retinal can move freely along the cone photoreceptor, but retinal either is not taken up by the rod cell body or retinal cannot move from the rod cell body to the rod outer segment. The free transfer of retinal along cone but not along rod photoreceptors could explain why, during dark adaptation in the retina, cones have access to a store of 11–cis retinal which is not available to rods. Additional experiments investigated the movement of retinal along bleached rod outer segments. The results indicate that retinal can move along the rod outer segment, but that this movement is slow, occurring at about the same rate as the regeneration of visual pigment.

On the nature of linkage between retinal rod outer-segment disk and cellular membrane

1994 ◽  
Vol 52 ◽  
pp. 28-29 ◽  
Author(s):  
A. M. Petrosian ◽  
J. E. Haroutounian
Keyword(s):  
Cell Membrane ◽  
Extracellular Space ◽  
Outer Segment ◽  
Mechanical Stability ◽  
Freeze Fracture ◽  
Cellular Membrane ◽  
Rod Outer Segment ◽  
Retinal Rods ◽  
Retinal Rod ◽  
Frog Retina

In the retina of most vertebrates the cone outer segment disk are in continuity with the cell membrane, thus intradisk space is part of the extracellular space. The rod disk membranes, except for some basal ones, appear to be separated from the cell membrane. On the other hand it has been shown the existence of filament-like structures connecting retinal rod disks to one another and with the cell membrane. However due to the lack of observation of either electron-dense or fluorescent extracellular tracer penetration into rod outer segments, it is believed that rod intradisk space is isolated from the extracellular space. This investigation elucidates upon the nature of filament-like linkage between retinal rod outer segment disk and cell membrane. An incubation solution with 10 times lower than normal osmolarity was used to osmotically explode isolated dark adapted frog retina.Membranes under this condition were observed by transmission electron microscopy (TEM) using the freeze-fracture replica technique. Regularly spaced filaments were observed that were continuous between outer segment disks and the cell membrane in the retinal rods (Fig. 1). Probably these connections have a supporting function providing mechanical stability of the rod outer segment structure.

scholarly journals Adaptations in rod outer segment disc membranes in response to environmental lighting conditions

2017 ◽  
Vol 1864 (10) ◽  
pp. 1691-1702 ◽  
Author(s):  
Tatini Rakshit ◽  
Subhadip Senapati ◽  
Vipul M. Parmar ◽  
Bhubanananda Sahu ◽  
Akiko Maeda ◽  
...  
Keyword(s):  
Outer Segment ◽  
Rod Outer Segment ◽  
Lighting Conditions ◽  
Environmental Lighting

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.

High time resolution enzyme cytochemistry of rod outer segment

1990 ◽  
Vol 48 (3) ◽  
pp. 878-879
Author(s):  
Takuma Saito ◽  
Toshihiro Takizawa
Keyword(s):  
Enzyme Activities ◽  
Outer Segment ◽  
Rapid Change ◽  
High Time Resolution ◽  
Visual Cell ◽  
Enzyme Cytochemistry ◽  
Activation Effect ◽  
Rod Outer Segment ◽  
Enzymatic Cascades ◽  
Rapid Drop

Cells and tissues live on a number of dynamic metabolic pathways, which are made up of sequential enzymatic cascades.Recent biochemical and physiological studies of vision research showed the importance of cGMP metabolism in the rod outer segment of visual cell, indicat ing that the photon activated rhodopsin exerts activation effect on the GTP binding protein, transducin, and this act ivated transducin further activates phosphodiesterase (PDEase) to result in a rapid drop in cGMP concentration in the cytoplasm of rod outer segment. This rapid drop of cGMP concentration exerts to close the ion channel on the plasma membrane and to stop of inward current brings hyperpolarization and evokes an action potential.These sequential change of enzyme activities, known as cGMP cascade, proceeds quite rapidly within msec order. Such a rapid change of enzyme activities, such as PDEase in rod outer segment, was not a matter of conventional histochemical invest igations.

Sign in / Sign up

Export Citation Format

Share Document