Cones retinal receptor

Fig. 1. Representative spectral sensitivities of the human retinal receptors, (-) scotopic (rod) vision, and P, y, and p cone sensitivities. The wavelengths of...

In colour vision there are three specific types of cone cell corresponding to red, green and blue receptors. The chromophore is the same for all three colours, being 11-cis-retinal bound to a protein which is structurally similar to opsin. Colour selectivity is achieved by positioning specific amino acid side chains along the chromophore so as to perturb the absorption spectrum of the chromophore. 

The evidence to-date shows that vertebrate photoreception is mediated by a closely related group of proteins termed opsins. These are G protein-coupled receptors characterized by their ability to bind a vitamin A based chromophore ( -cis-retinal) via a Schiff base linkage using a lysine residue in the 7th transmembrane a helix (Fig. 1). The primary events of image detection by the rods and cones occurs with the absorption of a photon of light by ll-r/r-retinal and its photoisomerization to the AUtrans state (Bums Baylor 2001, Menon et al 2001). Although photoreception is best understood in retinal rods and cones, photoreception is not confined to these structures. In non-mammalian... 

Rod and cone cells are the light sensitive receptor cells in the retina of the human eye. About three million rod cells are responsible for our vision in dim light, whereas the hundred million cone cells are responsible for our vision in the bright light and for the perception of bright colours. In the rod cells, ll-cw-retinal is converted to rhodopsin. 

The membranes of the rod discs are -60% protein and 40% lipid (Table 8-3). About 80% of the protein is rhodopsin (visual purple), a lipoprotein that is insoluble in water but soluble in detergent solutions. Digito-nin is widely used to disperse rhodopsin molecules because it causes no change in optical properties. In addition to rhodopsin, in the outer segment discs of frog retinal rods, there are -65 molecules of phospholipid and smaller amounts of other materials for each molecule of rhodopsin (Table 8-3). The cone cells have a similar architecture but have a different shape and contain different light receptors. The receptors in the cones are present in deep indentations of the plasma membrane rather than in discs within the cytoplasm. 

Cone cells, like rod cells, contain visual pigments. Like rhodopsin, these photoreceptor proteins are members of the 7TM receptor family and utilize 11-cA-retinal as their chromophore. In human cone cells, there are three distinct photoreceptor proteins with absorption maxima at 426, 530, and 560 nm (Figure 32.26). These absorbances correspond to (in fact, define) the blue, green, and red regions of the spectrum. Recall that the absorption maximum for rhodopsin is 500 nm. 

Vision is perhaps the best understood of the senses. Two classes of photoreceptor cells exist cones, which respond to bright lights and colors, and rods, which respond only to dim light. The photoreceptor in rods is rhodopsin, a 7TM receptor that is a complex of the protein opsin and the chromophore 11-ds-retinal. The absorption of light by... 

Glutamate s role as a neurotransmitter in the vertebrate retina is reviewed by Barnstable (1993), Brandstatter et al. (1998) and Lo et al. (1998). As the cell bodies of different retinal cell types are in different laminae (Fig. 10), we can assign which general cell types express which glutamate receptor subunits. However, there are different subsets of the same cell class, e.g., there are at least 10 different types of on- and off-bipolars, and multiple subtypes of the other cell classes (Stevens, 1998). Without cell-type markers and double-labelling studies, ISH can not differentiate these. The cones and rods release glutamate onto the bipolar cells only off-bipolars use ionotropic receptors at this synapse on-bipolars use the metabotropic receptor mGluR6 instead. The distribution of NMDA and non-NMDA receptor mRNAs in the retina is summarized in Fig. 10. 

Fan S-F, Yazulla S (2003) Biphasic modulation of voltage-dependent currents of retinal cones by cannabinoid CBl receptor agonist WIN 55212-2. Visual Neurosci 20 177-188... 

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