What does the transmitter do?
It binds to the channel resulting in the channel becoming opened. Ions flow selectively through the channel.
How many transmitter binding sites are there per receptors?
Usually more than one. Average 2.
What is the typical rate of ions to flow through a channel?
10 million ions per second.
What happens when nicotinic receptors are activated?
Leading to opening of the associated cation-conducting ion channel.
How many subunits are the nicotinic receptors made up of?
What technique is used to observe the activity of single receptors?
Use of the patch-clamp technique.
Describe the "patch-clamp technique"?
Fire-polish the tip of the electrode and connect it to the cell (using a syringe to suck).
Name the 4 different confirmations of the patch-clamp technique?
Cell attached. Whole-cell Inside-out Outside-out
What are the 2 advantages of using cell-attached patch?
1. Intracellular milieu is maintained. 2. Control of the extracellular solution.
What are the 3 disadvantages of using cell-attached patch?
1. Investigating different conc. of drugs. 2. Agonist always present. 3. No control of the intracellular content.
What are the 3 advantages of using whole-cell voltage clamp?
1. Control of the intracellular and extracellular milieu. 2. Record from a population of receptors. 3. Introduce biochemical modulators intracellularly.
What are the 2 disadvantages of using whole-cell voltage clamp?
1. Biochemical "washout" of the intracellular milieu. 2. Resolution- rarely observe single receptors.
What are the 2 advantages of using outside-out patch clamp?
1. Control of the intracellular and extracellular milieu. 2. Can change extracellular drug conc.
What are the 2 disadvantages of using outside-out patch clamp?
1. Biochemical "washout" of the intracellular milieu. 2. Cannot change intracellular messengers.
What are the 2 advantages of using inside-out patch clamp?
1. Control of the intracellular & extracellular milieu. 2, Can introduce biochemical modulators.
What is the 1 disadvantage of using inside-out patch?
Cannot change the concentration of agonist.
Is the nAChR selective or non-selective for cation channels?
The different confirmations of the nAChR?
Mainly it usually requires two agonist to bind before it opens. However, there is a chance that it will open when only one agonist is bound. Thus had a numerous different states. Bound closed (1A). Bound open (1A). Bound closed (2A) and bound open (2A)
What is the difference when the nAChR is opened by one agonist or two?
When one opens it it is only mono-liganded and is brief in its opening. When two opens it: it is bi-liganded therefore it is prolonged opened with brief closures.
Name two subtypes of nAChR?
Ganglionic and skeletal muscle.
What family is the nAChR a member of?
The cys-loop transmitter-gated ion channel family
What other receptors are the nAChR closely related to?
GABAA, glycine and 5HT3 receptors.
Name the 5 subunits that make up the nAChR?
alpha. Beta. Delta. Alpha. Epilson Usually: many different subtypes depending on function of the receptor
What part of the nAChR does the ACh bind?
ACh binds to the part between delta& alpha subunit and between alpha&epilson.
What part of the subunit does the ACh bind?
At the subunit interfaces.
Name the 3 transmitter-gated ion channel family of receptors?
Cys-loop receptor Glutamate receptor family. P2X receptor family.
What are the characteristics of the Cys-loop receptor superfamily?
Pentamer. NH3 and COO on the outside. eg. nAChR, GABAA and glycine.
What are the characteristics of the glutamate receptor family?
Tetramer. 4 subunits-> 2nd not fully spanning. eg. NMDA and AMPA receptor.
What are the characteristics of the P2X receptor family?
Trimer. eg. P2X receptor.
Whats a characteristic of the nACh receptor that is related to its function?
It has a large loop located between TM3 and TM4 located at the intracellular portion of the receptor.
Define the term "PAMs"?
Positive allosteric modulators.
Describe two-electrode voltage clamp?
Oocyte clamped at -60mV. Current passing at one end of the membrane and voltage sensing at the other end. Record what happen on application of neurotransmitter.
What relates subunit protein to function?
What is the agonist of the alpha 7 receptor?
What is the agonist of the 5-HT3A receptor?
What is the agonist of the alpha7/5HT3A receptor?
What does alpha-bungarotoxin do to the alpha 7 receptor?
Blocks the agonist from binding.
What does the alpha-bungarotoxin do to the 5-HT3A receptor?
What does the alpha-bungarotoxin do the alpha7/5HT3A receptor?
Blocks the agonist from binding
What is the conductance of the alpha 7 receptor?
What is the conductance of the 5-HT3A receptor?
What is the conductance of the alpha7/5HT3A receptor?
Where is TM2 amino acid located on the nAChR?
On the cation conductance.
Name two extracellular influences that can effect cation conductance?
Glutamate and aspartate.
How is cationic nAChR a7 mutated to anionic?
By mutating Glu to Arg of the M2 segment
How is anionic a1-GlyR mutated to cationic?
By mutating Arg to Glu of the M2 segment
Difference in conductance between homomeric and heteromeric 5HT3A receptors?
Homomeric has a lower conductance value compared to heteromeric.
Why is there a noticeable difference in conductance between homomeric and heteromeric 5HT3A receptors?
Changes within the intracellular loop between TM3 and TM4.
Where in the 5HT3A receptor is the determinant of conductance?
Mapped to 21 AAs in the large intracellular loop between TM3 and TM4.
Define the watering can model of ion conductance?
Ions were thought to travel straight through a channel while the watering can model suggests that the channel disperses ions in all direction when it passes through.