Taste

Question 1

What are the basic tastes?

Answer 1

Sweet, sour, umami, salt and bitter

Question 2

How is the topology for the 5 basic taste receptors?

Answer 2

Umami + sweet: dimeric GPCR (T1R1/2 + T1R3) - family C
Bitter: GPCR, app. 30, each bitter cell express all 30
Salt: Na^+ gated ion channel, trimer, each monomer has 2 TMs - DEG/ENaC family
Sour: H^+ gated ion channel, dimer, each monomer har 12 TMs - otop 1 family

Question 3

Descripe the signal transduction of sweet/umami/bitter.

Answer 3

Tastant binds and activates GPCR. G-q-beta-gamma activates PLC, which cleaves PIP2 into IP3 and DAG. IP3 gates a Ca^2+ channel on ER, Ca^2+ gates TRPM5 inducing Na^+ influx, resulting in depolarization triggering voltage gated Na^+ channels to open -> AP. The action potential results in the opening of voltage gated ATP channels (pannexin). ATP binds to P2X3 on afferent neuron, and the neuron is depolarized and an actionpotential is initiated -> signal travels to brain

Question 4

Describe the signal transduction of salt/sour.

Answer 4

Na^+/H^+ binds to ion channel, resulting in Na^+/H^+ influx, causing depolarization resulting in AP. Voltage gated Ca^2+ channels open, and stimulate the release of serotonine. Serotonine binds to 5HT3R on afferent neuron, causing Na^+ influx and AP -> signal travels to brain.

Question 5

Which receptors mediates the tasting of spices?

Answer 5

TRP channels, e.g. TRPV1: capsaisin (heat/pain) and TRPM8: menthol (cold)

Question 6

What pathway do the nerves sensing spices signal through?

Answer 6

The trigmenial ganglion