Lecture 3 - Taste Pt. 2

Question 1

How does the PKD2L1 promoter gene used for?

Answer 1

gene that is useful to mark sour cells it was thought to be the sour receptor but later shown that it does not function as the sour receptor

Question 2

What was used to identify sour taste cells?

Answer 2

PKD2L1 promoter driving YFP can be used to identify sour taste cells; recorded from the PKD2L cells and showed that APs to acid stimuli increase as pH is lowered

-Note the the Ba2+ in the study is a positive control since it blocks the resting potassium ion channels causing depolarization

Question 3

How do sour taste cells respond to acids?

Answer 3

with an inward H+ current

Question 4

What is the inward H+ current sufficient to elicit and what is it specific to?

Answer 4

APs; specific to sour taste cells

Question 5

What is the expression cloning strategy?

Answer 5

1. Isolate and pick cells
   10-15 YFP+/PKD2L1 (5 replicates)
   10-15 GFP+/TRPM5 (5 replicates)
2. Molecular Biology
   library generation
   sequencing
   map to genome
3. Analysis/Candidate selection
   TM protein
   Function unknown
   Enriched in PKD2L1 cells (4x)
   Not ubiquitous (bio GPS)

Question 6

What gene expressed currents that are evoked by lowering extracellular pH?

Answer 6

OTOP1 makes the ion channels that carries H+ protons into the cell
-the current is bigger as pH is lowered
-only protons go through the channel

Question 7

What was performed to figure out that Otop1 is required for acid-evoked APs in sour taste cells?

Answer 7

KO found animals not sensitive to acid stimuli and did not fire APs

Question 8

What is the model for sour taste transduction?

Answer 8

-a proton selective ion channel encoded by Otop1 opens in response to acidic stimuli which allows an influx of H+ ions (H+ both opens the channel and goes through it)
-this acidifies the cell cytosol which blocks the potassium channel
-the influx of H+ and closing of potassium leak channels depolarizes the membrane potential leading to the generation of APs and release of neurotransmitters

OTOP1 is the sour receptor

Question 9

What is the receptor for salty taste?

Answer 9

Na+ channels ENaC (epithelial sodium channel found first in the kidney)
-is open constitutively does not need voltage
-sodium enters through the ENaC and depolarizes the cel
-cell releases the neurotransmitter THROUGH A MECHANISM THAT DOES NOT INVOLVE VESICULAR RELEASE