Lecture 7: Sensing with ion channels - taste cells and the retina

Question 1

Chemotransduction

Answer 1

how taste cells work
taste cells are polarized
channel change lead to receptor potential

Question 2

salty

Answer 2

Na+ permeation through cation channels

Question 3

sour/acid

Answer 3

H+ block of K channels or permeation of H+ in mammals
in vertebrates H+ in through proton channel causes change in Vm (depolarization)
Na+ in K out Ca in increased Ca –> vesicles released

Question 4

sweet, umami and bitter

Answer 4

are GPCR and G-protein mechs
bind to G protein coupled receptor G proteins intimates second messenger system that induces Ca release from stores in things like ER

Question 5

Phototransduction in the dark vs light

Answer 5

Dark: the cells are depolarized, high release, large influx of Na+, high efflux of K+

Light: cells hyper polarized, low release less influx of Na+ and K+

Question 6

Mechanism of phototransduction

Answer 6

• photon absorption
• conformational change in rhodopsin a GCPR
• G-protein transduction activated
• PDE phosphodiesterase is activated
• Hydrolysis/decrease of cGMP
• closure of CNG channels

Question 7

how does light affect phototransduction

Answer 7

increases outward current and increases level of hyper polarization

Question 8

Cell types of the retina

Answer 8

retinal neurons are relatively depolarized in darkness
tonic release of glutamate
ribbon synapses in photoreceptors and bipolar cells basically synapsing on multiple types of cells for quick Ca+ mediated activation

Question 9

Ca+2 induce Ca+ release

Answer 9

• Ca+2 influx
• Ca+2 ions bind to RyRs
• Ca+2 released form stores ER to further increase cytosolic Ca+2
• low cytosolic Ca+2 is usually maintained by pump
• a little influx of Ca+2 across the membrane can release a lot of Ca+2 from the ER