GPCRs II Flashcards
Receptors associated with sense of smell
Olfactory receptors
Receptor associated with vision
Rhodopsin
Important signalling molecule in smooth muscle
Nitric oxide
Action potential sequence
Resting potential, depolarisation, repolarisation, hyperpolarisation
Muscarinic ACh receptor M2
Present on heart cells. ACh binds, Gi protein gets activated, Galpha subunit inhibits adenylyl cyclase. Beta-gamma subunits bind and open K+ channels, making it harder to depolarise the cell. Decreased rate of firing
How many olfactory receptors do humans have
~350
How many smells can human olfactory receptors detect
> 10, 000
What happens when an odorant binds to an olfactory GPCR?
Activates a Golf protein, which activates adenylyl cyclase. This produces cAMP which opens cAMP- gated Na+ channels, which depolarises the olfactory neuron.
What do cones detect
Colour
What do rods detect
Intensity
Structure of retina
Axons of ganglion cells, ganglion cells, bipolar cells (horizontal and amacrine cells), photosensors (rods and cones), pigmented epithelium
How many disks does 1 rod have
~1000
How many rhodopsins does 1 disk have
~150,000
Basics about rhodopsin
GPCR, detects change from 11-cis-retinal (a chromophore) to 11-trans-retinal caused by photon
Rod photoreceptor in the dark
Rhodopsin inactive, cation channels open, rod cell is depolarised, glutamate is released and inhibiting ON bipolar cell
Rod photoreceptor in the light
Rhodopsin active, cation channels close, rod cell is hyperpolarised, glutamate is not being released, ON bipolar cell is not being inhibited and fires an action potential. (cGMP phosphodiesterase is stimulated)
Guanylyl cyclase
GTP to cGMP
Rhodopsin G-protein
Transducin (Gt)
What is used to help the rods to adapt to continuous light exposure
Negative feedback loops (RGS (a GAP), rhodopsin kinase, arrestin)
What is the difference in membrane potential by 1 photn
1mV
Why is nitric oxide produced?
Produced in response to GPCR signalling in endothelial cells. NO diffuses into adjacent smooth muscle cells where it activates guanylyl cyclase, producing cGMP and causing rapid relaxation of the smooth muscle cell.
