Activation of the phototransduction cascade

Stable Identifier
Homo sapiens
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The photoreceptor cascade starts with light isomerization of 11-cis-retinal (11cRAL) of rhodopsin (RHO) to all-trans-retinal (atRAL), inducing a conformational change in RHO to the active, metarhodopsin II (MII) state. MII activates the G protein transducin (Gt) that in turn activates phosphodiesterase 6 (PDE6). Consequently, there is a fall in the intracellular concentration of cGMP that closes cGMP-dependent cation channels (CNG channels) and hyperpolarizes the rod. This has the effect of reducing or stopping glutamate release from synaptic vesicles thus signalling to the surrounding cells how many photons were absorbed (Burns & Pugh 2010, Korenbrot 2012, Pugh & Lamb 1993).

Literature References
PubMed ID Title Journal Year
22658984 Speed, sensitivity, and stability of the light response in rod and cone photoreceptors: facts and models

Korenbrot, JI

Prog Retin Eye Res 2012
8382952 Amplification and kinetics of the activation steps in phototransduction

Pugh, EN, Lamb, TD

Biochim. Biophys. Acta 1993
20430952 Lessons from photoreceptors: turning off G-protein signaling in living cells

Burns, ME, Pugh, EN

Physiology (Bethesda) 2010
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