The phototransduction machinery in the rod outer segment has a strong efficacy gradient

Rod photoreceptors consist of an outer segment (OS) and an inner segment. Inside the OS a biochemical machinery transforms the rhodopsin photoisomerization into electrical signal. This machinery has been treated as and is thought to be homogenous with marginal inhomogeneities. To verify this assumption, we developed a methodology based on special tapered optical fibers (TOFs) to deliver highly localized light stimulations. By using these TOFs, specific regions of the rod OS could be stimulated with spots of light highly confined in space. As the TOF is moved from the OS base toward its tip, the amplitude of saturating and single photon responses decreases, demonstrating that the efficacy of the transduction machinery is not uniform and is 5–10 times higher at the base than at the tip. This gradient of efficacy of the transduction machinery is attributed to a progressive depletion of the phosphodiesterase along the rod OS. Moreover we demonstrate that, using restricted spots of light, the duration of the photoresponse along the OS does not increase linearly with the light intensity as with diffuse light.

Download Full-text

Movement of retinal along cone and rod photoreceptors

Visual Neuroscience ◽

10.1017/s0952523800001735 ◽

1994 ◽

Vol 11 (2) ◽

pp. 389-399 ◽

Cited By ~ 29

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.

Download Full-text

High time resolution enzyme cytochemistry of rod outer segment

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100161953 ◽

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.

Download Full-text