Sensing with channels

Question 1

Senses and ion channels

Answer 1

Photoreception and olfaction (cNGCs)

Gustation, hearing and touch (TRP channels)

Question 2

Vertebrate and drosophila phototransduction

Answer 2

Vertebrate cGMP-gated channel
Light leads to hyperpolarisation (channel closes and Na+/Ca2+ influx blocked)

Drosophila TRP/TRPL
Light leads to depolarisation (channel opens and allows Na+/Ca2+ influx)

Question 3

TRP channel features

Answer 3

6 TMS domains (S1-6)
1 pore (P) domain. Cation selective (usually preference for Ca2+ over Na+)
No voltage sensor
Long C and N termini (regulation of gating)
Highly promiscuous gating (DAG, PIP2, Ca2+, GTP)

Question 4

Thermosensation

Answer 4

TRPV1, 2, 3, 4 activated by heating
TRPM8, TRPA1 activated by cooling
TRPM2 required for warmth sensing
TRPV1 deficient mice lack neurons that respond to moderate heat
Neurons from TRPM8- mice show loss of cold sensitivity

Question 5

Thermosensing mechanism

Answer 5

TRPV1 channel opening is favoured as the temperature increases
TRPM8 channel closing is favoured as the temperature increases

Question 6

Mechanosensation and hearing

Answer 6

TRP channels on stereocilia connected by tiplinks
Movement of cilia opens/closes ion channel
TRPA1 highly expressed in hair bundles
Ankyrin binding repeat binds to cytoskeleton

Question 7

Chemosensation

Answer 7

Capsaicin binds to TRPV1, menthol binds to TRPM8 (both also thermosensors)

Tyrosine-serine motif between TM2 and TM3 important for capsaicin binding