BISC306 Lecture Notes - Lecture 12: Opsin, Rhodopsin, Phosphodiesterase
5 Oct 2016
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Visual transduction: photoreception & visual fields: photoreception, rods & cones-hyperpolarize when exposed to light and release less neurotransmitter a. i. Depolarize in the dark and release glutamate neurotransmitter a. ii. Light decreases the [na+] conductance in outer segments a. iii. Channels are gated by cyclic-gmp: dark current-positive charge comes in during dark light and cyclic-gmp (cgmp) levels increase and na+ channels open b. i. Opened by the binding of cgmp to the protein this allows na+ and ca+2 to enter into the cell: light absorption-causes pigment cis-retinal to change the all-trans configuration c. i. Cis-retinal-bound to a g-protein coupled receptor called opsin in the membrane of rods and cones c. i. 1. Cis-form binds and makes a covalent linkage which causes a conformation change & becomes activated c. ii. Rhodopsin is absorbed, cgmp binds and eventually opens na+ channels cgmp acculumutaes in dark adapted eyes and the channels are more likely to be opened c. ii. 3. cgmp phosphodiesterase c. iii.
