Preferred Label : Visual Signal Transduction Pathway;
NCIt related terms : Visual Signal Transduction;
Alternative definition : BIOCARTA: The signal transduction cascade responsible for sensing light in vertebrates
is one of the best studied signal transduction processes, and is initiated by rhodopsin
in rod cells, a member of the G-protein coupled receptor gene family. Rhodopsin remains
the only GPCR whose structure has been resolved at high resolution. Rhodopsin in the
discs of rod cells contains a bound 11-cis retinal chromophore, a small molecule derived
from Vitamin A that acts as the light sensitive portion of the receptor molecule,
absorbing light to initiate the signal transduction cascade. When light strikes 11-cis
retinal and is absorbed, it isomerizes to all-trans retinal, changing the shape of
the molecule and the receptor it is bound to. This change in rhodopsin's shape alters
its interaction with transducin, the member of the G-protein gene family that is specific
in its role in visual signal transduction. Activation of transducin causes its alpha
subunit to dissociate from the trimer and exchange bound GDP for GTP, activating in
turn a membrane-bound cyclic-GMP specific phosphodiesterase that hydrolyzes cGMP.
In the resting rod cell, high levels of cGMP associate with a cyclic-GMP gated sodium
channel in the plasma membrane, keeping the channels open and the membrane of the
resting rod cells depolarized. This is distinct from synaptic generation of action
potentials, in which stimulation induces opening of sodium channels and depolarization.
When cGMP gated channels in rod cells open, both sodium and calcium ions enter the
cell, hyperpolarizing the membrane and initiating the electrochemical impulse responsible
for conveying the signal from the sensory neuron to the CNS. The rod cell in the resting
state releases high levels of the inhibitory neurotransmitter glutamate, while the
release of glutamate is repressed by the hyperpolarization in the presence of light
to trigger a downstream action potential by ganglion cells that convey signals to
the brain. The calcium which enters the cell also activates GCAP, which activates
guanylate cyclase (GC-1 and GC-2) to rapidly produce more cGMP, ending the hyperpolarization
and returning the cell to its resting depolarized state. A protein called recoverin
helps mediate the inactivation of the signal transduction cascade, returning rhodopsin
to its preactivated state, along with the rhodopsin kinase Grk1. Phosphorylation of
rhodopsin by Grkl causes arrestin to bind, helping to terminate the receptor activation
signal. Dissociation and reassociation of retinal, dephosphorylation of rhodopsin,
and release of arrestin all return rhodopsin to its ready state, prepared once again
to respond to light. (This definition may be outdated - see the DesignNote.);
NCIt note : The BIOCARTA Definition (ALT_DEFINITION) for this pathway concept was provided by
BioCarta. This property was not created by, nor is it maintained by the NCI Thesaurus
staff. Additionally, BioCarta is no longer updating its pathway data; thus, the BIOCARTA
Definition might be outdated or inaccurate. Please see the Terms and Conditions for
Use at http://www.biocarta.com/.;
Biocarta ID : h_rhodopsinPathway;
Origin ID : C39222;
UMLS CUI : C1520031;
Automatic exact mappings (from CISMeF team)
- Semantic type(s)
- has_gene_product_element
- pathway_has_gene_element
