Drugable targets

Question 1

where is acetylcholine stored ?

Answer 1

Acetylcholine is present in vesicles of the presynaptic cell.

Question 2

synthesis of acetylcholine ?

Answer 2

Acetylcholine is synthesised within these vesicles from choline, which is transported into the nerve terminal by a specific transporter, it transports choline not acetylcholine so it is not involved in the termination of the transmitter , also present in the vesicles is ATP which drives this process

Question 3

cholinesterase ?

Answer 3

Present in the vesicles is an enzyme called cholinesterase and this continually hydrolyses the acetylcholine and resynthesises it, if this enzyme is inhibited then this leads to very high intracellular levels of Ach which is not available for release by the nerve terminal.

Question 4

what triggers the release of acetylcholine from vesicles and what occurs ?

Answer 4

These vesicles containing acetylcholine are contained at a very high concentration about 100mmol/l. The release from the vesicles occurs by exocytosis and following ca2+ entry into the nerve terminal, a series of events leads to the acetylcholine vesicle in the presynaptic cleft to dock and bind to the membrane of the cell. This leads to it releasing its contents, and it crosses the synaptic cleft to activate the post junctional receptor.

Question 5

enzyme acetylcholine esterase ?

Answer 5

Following release in the synaptic cleft some of the acetylcholine is hydrolysed by the enzyme acetylcholinesterase into choline and acetate this is so the effects are produced rapidly. Choline is charged so it can’t pass the fatty bilayer, therefore a high affinity transporter molecule is recruited so it can cross the membrane

Question 6

choline acetlyl transferase ?

Answer 6

intracellular enzyme called choline acetyl transferase, during this the free choline is acetylated and the acetyl group from Acetyl-CoA is transferred.

Question 7

rate limiting step of acetylcholine transport ?

Answer 7

The rate limiting step in the synthesis of Acetylcholine is the choline transport which is determined by the concentration of extracellular choline

Question 8

Monoamineoxidases found ?

Answer 8

At the varicosity of a neuron there are extracellular enzymes called monoamineoxidases. There are also several different types of receptors present on the post synaptic cell for example 5-HT , alpha , beta , dopamine and purinergic receptors. In a facilitative nerve ending , they won’t contain all of these receptor types , just one. These receptors will also contain ATP to aid Transportation

Question 9

synthesis of 5-HT ?

Answer 9

For the synthesis of 5-HT the precursor is the amino acid tryptophan, this is carried across the bilayer by amino acid transporters as they are unable to cross the bilayer themselves as they are charged. Tryptophan is then converted to 5-hydroxytyrptophan by the enzyme tryptophan hydroxylase. This is then decarboxylated to 5-HT by an amino acid decarboxylase. .

Question 10

5-HT normally stored ?

Answer 10

5-HT is often stored in neurons and chromaffin cells as a co transmitter alongside other peptide hormones

Question 11

degredation of 5-HT ?

Answer 11

The degradation of 5 HT is normally through the oxidation deamination from the enzyme monoamine oxidase.

Question 12

dopamine synthesis ?

Answer 12

Dopamine is a metabolic precursor to noradrenaline and adrenaline. The metabolic precursor for noradrenaline is L-tyrosine , an amino acid. This requires transport across the bilayer as it cannot cross itself as it is charged. The L-tyrosine is then converted to dihydroxyphenylalaine (dopa) by the enzyme tyrosine hydroxylase. Dopa is then converted to dopamine by the a cytosolic enzyme called dopa decarboxylase

Question 13

how is 5-HT and dopamine transported to the vesicles ?

Answer 13

Both dopamine and 5-HT is then transported into vesicles with the aid of ATP, for 5-HT this is the last step for it’s synthesis , however dopamine can further be converted into noradrenaline and adrenaline

Question 14

drugs can affect the storage in vesicles ?

Answer 14

Drugs can affect the storage of chemicals in vesicles. A false neurotransmitter is a compound that enters the biosynthetic pathway and is present in synaptic vesicles and leads to the formation of a false neurotransmitter which is unable to activate the post synaptic receptors. As, the false neurotransmitter occupies a lot of the receptors, this prevents the real transmitter binding and as a consequence the response is hindered. For example, the real neurotransmitter is the biosynthetic pathway of L-dopa into dopamine and noradrealine , the false neurotransmitter is alpha methyl dopa being converted into alpha methyl dopa and resulting in the formation of alpha methlynoradrenlaine. There is no alpha 1 receptor activity with alpha methyl dopa so it has no effect on contraction in the blood vessels but it has an effect on the alpha 2 receptors located in the periphery and brain , this reduces the amount of neurotransmitter being released.

Question 15

drugs can affect metabolism of neurotransmitters ?

Answer 15

Drugs can also affect the metabolism of neurotransmitters, they can do this by affecting their uptake inhibitors. There is a particular monoamine transporter that transports the neurotransmitter back into the vesicle. Uptake one transports the neurotransmitter from the extracellular space back into the nerve terminal, for example noradrenaline has a mitochondrial enzyme called monoamine oxidase (MAO) that does this. The role of MAO’s is that they reduce the level of free neurotransmitter in cells. By preventing the breakdown of neurotransmitters we can therefore, increase the level of them in the synapse.

Question 16

moclobemide ?

Answer 16

Moclobemide is a drug that acts on monoamine A to treat social anxiety and depression

Question 17

selegiline ?

Answer 17

selegiline works on monoamine B to treat depression and increase dopamine levels as a possible cure for Parkinson’s

Question 18

zerpine ?

Answer 18

Zerpine blocks the reuptake of neurotransmitter into the vesicle , it is not a clinical drug however , it is just used in the lab

Question 19

fluoxetine ?

Answer 19

Fluoxetine is a SSRI which is selective serotonin reuptake inhibitor ,

Question 20

venlafaxine ?

Answer 20

venlafaxine is a SNRI which is a selective noradrenaline reuptake inhibitor.

Question 21

sympathomimetics ?

Answer 21

Sympathomimetics are indirectly acting agonists that mimic the aspects of the sympathetic nervous system and leads to the release of noradrenaline.

Question 22

tyramine ?

Answer 22

sympathomimetics

Question 23

ephedrine ?

Answer 23

found nasal sprays

Question 24

amphetamine mode of action ?

Answer 24

Amphetamine is taken into the vesicle by reuptake 1 alongside the other neurotransmitter noradrenaline present. If amphetamine is taken up in high enough concentrations, then it will prevent the noradrenaline neurotransmitter from being taken up and increase the level of neurotransmitter present in the neuronal cleft. Amphetamine is taken up by the MAO transporter and this displaces the noradrenaline from the vesicles , some of the displaced noradrenaline will be re uptake by MAO however some will be pumped out from the vesicle and activate the post synpatic cell.

Question 25

calcium channels explained for structure ?

Answer 25

The calcium channel contains an alpha subunit, which is responsible for the pore forming element. The channel is made up of 4 domains and each domain is made up of 6 separate transmembrane units. The main alpha sub unit is divided into 3 groups based on their molecular pharmacology ,these are Cav1 , Cav2 and Cav3.

Question 26

calcium channel compared to sodium ?

Answer 26

calcium channels are activated when the membrane is depolarised and on comparison to sodium channels , they require a stronger depolarisation to open. They also activate and inactive more slowly than sodium channels. The calcium channels supply a maintained inward current for a prolonged depolarisation which is important in the plateau phase of the cardiac action potential.

Question 27

type L calcium channel?

Answer 27

Type L calcium channel is found in many cells an the plasma membrane , it is voltage gated and the drugs that target it are verapamil , nifedipine and diltiazem.

Question 28

type N calcium channel ?

Answer 28

Type N calcium channels are found in nerve terminals and it is voltage gated. The drugs that target it are huwentoxin XVI and Prialt

Question 29

type T calcium channel ?

Answer 29

Type T calcium channels are found in cardiac pacemaker and they are voltage gated, drugs targeted against it are mibefradil and trimethadione

Question 30

P/Q calcium channel ?

Answer 30

P/Q calcium channels are found in ER/SR and they are gated by IP3, drugs that target it are 2-APB.

Question 31

ryanodine calcium channel ?

Answer 31

Ryanodine calcium channels are located in the ER/SR and are gated by calcium ion. The drugs that target it is ryanodine

Question 32

sodium channel explained ?

Answer 32

Sodium channels contain 11 genes (SC1A-SCN11A) , they encode for nine channels (Nav1.1-Nav1.9). There is a 50% homology for the amino acid sequence between the different sodium channels so it is difficult to find a drug target.

Question 33

explain resting state and activation ?

Answer 33

The channel contains 2 paddles as voltage sensors, the pinch point is the selectivity filter. At rest the outside of the membrane is positively charged and inside is negatively charged. The paddles are positively charged so they are attracted to the negative inside of the membrane and gate remains closed. During a depolarisation the inside of the cell becomes more positively charged. The paddle moves up and ions can flow down their concentration gradient. Based on the selectivity filter, only one ion will move into the cell, in this case it’s a sodium. Sodium channels have a ball and chain of amino acids which are attracted to the inside of the membrane based on hydrophobic interaction which blocks channel from the inside even though it is still open. The sodium channel has 3 states, closed, open and inactivated (even during depolarisation).

Question 34

potassium channel ?

Answer 34

Potassium channels are 6TM with one pore and some are 2 TM and a pore , some are 4TM with 2 pores. They are able to depolarise membranes , quickly or can delay depolarisation.

Question 35

ATP a regulator for ?

Answer 35

ATP is a regulator of the membrane potential , KATP channels are important in regulating the membrane potential in smooth muscle and pancreatic beta cells.

Question 36

KATP in smooth muscle ?

Answer 36

The kATP channels in smooth muscle cells are normally bound with ATP and this causes the ion channel to remain closed. In a resting state smooth muscle cell there is normally an excess of ATP. When the cells enter the active phase there is calcium entering the cell, the ATP is broken down into ADP and as a result the ATP levels decrease and ADP increases. The sulfonylurea ion channels lose their bound ATP and this causes the potassium channels to open and potassium moves down it’s concentration gradient out of the cell resulting in a decrease in the membrane potential. As a result , the membrane potential moves closer to the resting value and the calcium channels close as a result. The levels of ATP affect the potassium levels in a cell and as a result this indirectly has an effect on the calcium levels.

Question 37

beta cells kATP ?

Answer 37

In a beta cell, the kATP channel is opened in resting state as the ATP levels are low. When glucose levels increase they enter the beta cells and this transforms ADP + Pi into ATP. The ATP binds to the sulfonylurea receptor which blocks the ion channel , as there is no longer a loss of charges the membrane potential depolarises and calcium channels open and calcium increases which drives insulin secretion.

Question 38

chromakalim ?

Answer 38

vasodilator

Question 39

glibenclamide ?

Answer 39

anti diabetic drug

Question 40

expression of T cell Kv1.3 potassium channels ?

Answer 40

correlates with pro inflammatory cytokines and disease activity

Question 41

why would a peptide drug have an advantage ?

Answer 41

they are highly selective and potent , so less chance of unusual side effect. The disadvantage is that they are expensive to make and how do they get past the low pH of the stomach?