Oral Biology, 10/24/11

Front 1

Name all the cell types in the taste bud

Back 1

-basal cell: undifferentiated
-Merkel like basal cell (type 4)
-Dark cell (type 1)
-light cell - type 2 (most important in taste)
-intermediate cell (type 3)

Front 2

Describe the functions of all the cell types

Back 2

Type II cells have taste receptors, but no synaptic contacts.
Type II cells signal to Type III cells, that then release neurotransmitters serotonin and ATP.
Type IV cell releases serotonin and has synaptic contacts.
Type I cells control intercellular fluid ionic make-up (Na+ and K+ levels).

Front 3

5 categories of taste and examples

Back 3

Sweet-
carbohydrates (sucrose, glucose) and some amino acids (aspartame)

Salty-
Monovalent cations (sodium, potassium)

Bitter-
Many different chemicals are bitter; some of these are toxic

Sour-
Acids and low pH

Umami- (savory)
Amino acid or peptide taste enhancers such as monosdium glutamate (MSG)

Front 4

How are taste receptors organized on the tongue?

Back 4

Not uniform; salt, sweet, etc. all detected in separate parts of the brain. All areas of the tongue express all known receptors.

-Detection of each tage category is mediated by receptors located on cell surface of taste cells.

Front 5

What are some clinical reasons for why understanding taste is important?

Back 5

-Taste blindness + deficiencies
-Nutrition
-Taste receptors are chemosensors for nutrients /toxins in other areas of alimentary tract

Front 6

What were early experimental studies about taste based on?

Back 6

Early studies were based on measurements of
changes in the levels of candidate mediators of
receptor-signaling in the tongue after giving rats
a taste stimulus.

Front 7

What chemical molecule were most early studies related to? Describe the animal study done on taste sensation.

Back 7

Began with second messengers. One of these was cAMP. Levels of cAMP changes in tongue in response to giving animals something they could taste: sugar, bitter, etc.
-cAMP increased dramatically after sugar and bitter compounds on tongue of rats.

made by conversion of ATP by adenylate cyclase.
Placed inhibitor compound 4,6 dichloro 4,6 dideoxy-alpha-galactopyranoside to sweet where cAMP does not increase.

Front 8

What type of studies can be done for the physiology of taste sensation (for sweet and bitter)

Back 8

Measure voltage across the cell through patch clamp study.

For sweet substances, K channels are closed.
Bitter - Ca channels are closed.

cAMP in sweet, make ion channel open. In bitter, it releases intracellular calcium during storage.

Front 9

cAMP activates what type of receptor? How does cAMP cause changes in cell physiology? (for sweet and bitter)

Back 9

G protein coupled receptors. Inactive - GDP.
Active - GTP. Receptor changes confirmation in G proteins; GDP is released, GTP is put in. Now this binds and activates AC and cAMP is now made from ATP.

Bitter- GTP activates phospholipase C. IP3 releases Ca from intracellular storage.

Front 10

What is Gustducin?

Back 10

First G protein: 1 of 3 that works with some receptors.
-certain receptors work with specific G proteins to conduct the signal. Within receptors + G proteins, sequences are highly conserved one can use PCR to fish for G proteins or receptors.
-Primers recog these sequences to find new proteins.

Knock out mice - less response to sweets, no changes in other flavors. Decrease AP of taste response to sweet and bitter substances.

Front 11

How can you tell whether mice can taste sweet or bitter substances?

Back 11

Behavioral studies - count number of times he goes to bitter vs. sweet substances.
-knock out mouse - takes higher concentration in order to him to avoid bitter. doesn't like sweet.

Front 12

Describe the study that identified the first taste receptor..

Back 12

Receptors that work with G-proteins have features unique to each individual receptor, and features common to all receptors in this class.
Thus, cDNA libraries made from taste cell RNA’s were screened for mRNA’s containing the common features of the G-protein receptor class.
These first receptors (T1R1 and T1R2) were not always co-expressed with gustducin, however, but otherwise were expressed by taste cells in a way that is consistent with being taste cell receptors (Cell 96, 541 – 551 (1999).
High topographic selectivity
Localized at or near the taste pore of taste buds
Mouse and human genes (orthologues) were identified and cloned in this first study of two putative taste receptor genes


TR1 or 2 don't have much to do with sweet or bitter. Gustducin is primarily for sweet + bitter.

TR1R1, TR1R2: taste pore opening.

Front 13

Describe the genetics/genomics approach

Back 13

-inherited "taste blindness" - linked to variation in chr5.
-T2R receptors were found on chr5,12, and 7. There's at least 100 related genes, all G protein coupled taste recept. genes in human genome.

-regions were correlated well with taste blindness.. This is how T2R family was discovered.

Front 14

What was found about T2R receptors on tongue?

Back 14

Consistent non-random distribution where bitter is detected. These are also localized with gustducin in the same taste cells.

-T2R and T1R do not localize with each other.

Front 15

Do we have more sweet or more bitter taste receptors?

Back 15

Most compounds are bitter and toxic. We have evolved to dislike bitter and we have more receptors to detect the bitter compounds out there.

Front 16

T2R5 receptors is specific for what?

Back 16

Cycloheximide was able to activate receptor combination for T2R5-Glustducin.

Front 17

What is the only sweet taste compound?

Back 17

T1R3 + T1R2 - different sweet tastants binds to different domains to the receptor. Need much higher levels to detect sweet.

Front 18

How many bitter taste receptors are there?

Back 18

30! All variants in T2R. Each receptors homo and heterodimer recognizes different kinds of bitter tastants.

Umami T1R1 + T1R3 dimer: regonizes MSG + other amino acids.

Front 19

Describe sour taste receptors

Back 19

-Ion channel receptors.
-PKD2L - sour taste - low pH (high H) detector. Activation will release serotonin.

-First found in kidney disease (polycystic kidney disease). Later expressed in taste cells leading to discovery in sour taste receptors.
PKD1L3 now known to be Na channel.

Front 20

Salt taste receptors

Back 20

-TRPV1t: increases intracellular Ca, activating protein kinase C and P13 kinase. TRP1Vt - ion channel.

-ENaC: inhibited by amiloride. activated in high salt concentration.

Front 21

Are individual taste cells dedicated to a specific taste?

Back 21

-Afferent nerve fibers carry variety of signals to brain = blending
OR
-"Hard wired" - taste cells communicate to brain from specific flavor; known as labeled line model. Swapping receptors on same taste cells tests in this model.

Front 22

What is the evidence to the in line model?

Back 22

-Substitute ligand binding domain of taste receptor in sweet taste cells. Now expresses bitter receptors.
-This results in mice "liking" bitter compound.

Recent study:

1. place electrodes on mice that sense where Ca is released. Then instead of electrode, use dye that responds to Ca. Can identify general area of brain to see what area was stimulated: insular cortex.

; can identify what neuron was conducting the response.
-Different nerve cells respond to diff tastants: different locations in brain detect each flavor.

3. wild type + taste receptor knockout mice combined with fluroscent Ca sens dyes.

Front 23

Describe studies about finding taste receptor cells and response in the gut

Back 23

-Apetite suppressing hormones can be activated by activating sweet taste receptor in the gut.
GLP-1, GYY, and CCK = all apetite suppressants. Desire to overeat becomes limited and may treat diabetes + obesity.

Front 24

Where have sour taste receptors been found elsewhere in the body?

Back 24

Neural tissues - used as pH sensor.

Front 25

What enzyme is located on the tongue and taste pores?

Back 25

Carbonic anyhydrase - generates HCO3- and H+ from CO2 and H20. When CO2 comes into oral cavity, carbonic anhydrase comes along and metabolizes it. We detect activation of sour taste receptor. Invovled in detection of carbonation.

Front 26

here else can bitter taste receptors be found?

Back 26

Airway epithelium - helps to elicit gag response. Bitter taste receptors co localize with acetylated tublin present in motile cilia of airway epithelia.
-Ca is released in response to bitter compounds - denatonium and thujone.
-T2R1s, gustducin and phospholipase C by intratracheal admin led to receptor agonists leading to slower breathing in mice.

Front 27

What are some practical implications for discovering taste cells and receptors?

Back 27

Structure-based design of new substances with predicted taste
Salt substitutes
Sugar substitutes
Other flavor enhancers

New therapeutic strategies
New understanding of physiology in other tissues that will help in curing chronic diseases