Download Q. - IS MU

Receptors of
Hormones & Neurotransmitters
Seminar No. 8
- Chapter 22 -
1
Q.
What are general features of signal molecule?
(see scheme on p. 130)
2
Signal molecule (e.g. hormone)
• carries information into cell
• has extremely low concentration in blood (10-9 – 10-15 mol/l)
• specifically binds to receptor
• signal molecule is quickly inactivated
• agonist – (external) molecule which acts the same way as
physiological signal molecule
• antagonist – (external) molecule which blocks receptor
 no biological response
3
Q.
What is the amplification of signal?
4
Amplification of signal
= to make it more powerful
1 molecule of hormone
~ 100-1000 molecules of second messenger
second messenger transfers information to other
intracellular systems and then is quickly inactivated
5
Two classes of hormones
Feature
Lipophilic hormone
Hydrophilic hormone
steroids, iodothyronines,
calcitriol, retinoids
aminoacid derivatives,
polypeptides, proteins
Water solubility
no
yes
Transport protein*
yes
no
Plasma half-time
long (hours, days)
short (minutes)
Chemical type
Membrane penetration yes
no
Receptor
intracellular
in cell membrane**
Second messenger
hormone-receptor complex
cAMP, Ca2+ ....
* in blood
** hormone acts without entering the cell
6
Concentration of hormone in blood
generally does not correlate with its
biological effects
More factors are involved (transport systems,
chemical modifications, activity of receptors etc.)
7
Factors involved in biological action of hormones
Hormone synthesis
regulation effects
Hormone storage
feed back
Hormone secretion
secretion impuls
Transport in ECF
metabolism
inactivation
excretion
Receptor in target cell
cell condition
Biological response
8
Two principal types of receptors
• membrane receptors
• intracellular receptors
9
The main types of membrane receptors
Ligand gated ion channels
• in synapses, activated by neurotransmitters, very quick response
Receptors activating G-proteins
• stimulate or inhibit adenylate cyclase /phospholipase C
Receptors with guanylate cyclase activity
• atrial natriuretic factors
Receptors with tyrosine kinase activity
• insulin
10
Nicotinic acetylcholine receptor
• transmembrane protein = channel for Na+ and K+
• heteropentamer (α2βγδ)
• α-subunits have two binding sites for acetylcholine (ACH)
• nicotine is agonist of this receptor
11
Four events on postsynaptic membrane
(see the scheme and the graph on p. 131)
1. ACH binds to receptor  channel opens  influx of Na+ and
efflux of K+
2. partial depolarization of membrane (-60  -40 mV) opens other
type of voltage-dependent Na+-channel  further influx of Na+
 depolarization of postsyn. membrane ( +20 mV)
3. this depolarization opens K+-channel (volt. dep.)  efflux of K+
 membrane potential returns to normal value (-60 mV) =
repolarization
4. Na+,K+-ATPase gets ion distribution to normal state
(Na+  OUT,
K+  IN)
12
Q.
Describe the formation of acetylcholine in the body.
13
Acetylcholine
CH3
CH3
acetyl-CoA
N CH2CH2OH
CH3
choline
cholin
CH3
CH3
N CH2CH2
O
O C CH3
CH3
acetylcholin
acetylcholine
food
free choline or phosphatidylcholine
14
GABA receptor
• channel for chloride ion (Cl-)
• has the binding site for GABA  channel opens  Cl- ions
get into cell  hyperpolarization ( -80 mV)  decrease
of excitability
• benzodiazepines and barbiturates (synthetic substances)
have similar effects like GABA, they are used as anxiolytics
and/or sedatives
• endozepines – endogenous peptides have opposite effects,
close the channel (are responsible for anxiety feelings)
15
Q.
Describe the synthesis of GABA.
16
GABA formation
HOOC CH2
CH2
CH COOH
NH2
glutamát
glutamate
- CO2

HOOC CH2

CH2

CH2
NH2
GABA
gama-aminobutyric acid
the reaction requires:
enzyme (decarboxylase) + cofactor (pyridoxal phosphate)
17
GABA inactivation
GABA
succinate aldehyde
oxid. deamination
- NH3
oxidation
succinate
CAC
18
Diazepine
Benzo[f]diazepine
1
N a 2
N
b
f
N
N
4
diazepine is a seven-membered unsaturated heterocycle
with two nitrogen heteroatoms in the positions 1,4
19
Benzodiazepines
CH3
N
O
N
Cl
CH3
O
N
N
O2N
CH3
N
O
N
Cl
F
diazepam
flunitrazepam
tetrazepam
anxiolytic / sedative
hypnotic
myorelaxant
structural modifications lead to different pharmacological effects
20
Barbiturates
O
H
O
N
R1
R2
N
O
allobarbital:
R1 = R2 = -CH2-CH=CH2
H
derivates of 2,4,6-trioxoperhydropyrimidine
21
G-Protein linked receptors (scheme, p. 132)
• extracellular part of receptor has a binding site for hormone
• intracellular part has a binding site for G-protein
• G-proteins are heterotrimers (αβγ)
• in resting state, α-unit has GDP attached
• after binding hormone  (α-GDP)βγ makes complex with
receptor  GDP is phosphorylated to GTP
• activated G-trimer dissociates: (α-GTP)βγ  α-GTP + βγ
• α-GTP interacts with effector (enzyme)  activated/inhibited
enzyme  second messenger (↑ or ↓)
22
Main types of G-proteins
• Gs (stimulatory)
• Gi (inhibitory)
• Gp (phospholipid)
• and other ...
• see table on p. 132 !!
23
Q.
What reaction is catalyzed by adenylate cyclase?
24
Adenylate cyclase reaction
O
O
O
O
O P O P O P O
O
O
O
O
Adenin
O
- diphosphate
ATP
OH
Adenin
OH
O P
O
OH
O
cAMP
cAMP = cyclic 3’,5’-adenosine monophosphate
25
Adenylate cyclase (AC)
• membrane bound receptor
• catalyzes reaction: ATP  cAMP + PP (diphosphate)
• Gs protein stimulates AC  conc. of cAMP ↑
• Gi protein inhibits AC  conc. of cAMP ↓
26
Q.
What is the function of cAMP?
27
cAMP is the second messenger
• cAMP activates protein kinase A  phosphorylation of cell
proteins:
• Protein-OH + ATP  Protein-O-P + ADP
------------------------------------------------------------------------• the second messenger cAMP is quickly inactivated
• cAMP is removed by hydrolysis, catalyzed by
phosphodiesterase:
• cAMP + H2O  AMP
28
General scheme of phosphorylation
O
OH
O
Ade
O
O P O P O P O Rib
+
O
O
O
ATP (4-)
substrate
(protein)
substrát
protein
kinasakinase
O
O
O P O
O
O
Ade
+ O P O P O Rib + H
O
O
phosphorylated
protein (2-)
fosforylovaný substrát
(2-)
ADP (3-)
29
Q.
Which aminoacids can be phosphorylated?
30
A.
• AA with a hydroxyl group in a side chain
• serine
• threonine
• tyrosine
write the structural formulas
31
Q.
What reaction is catalyzed by protein phosphatase?
32
A.
Protein-O-P + H2O  Protein-O-H + Pi
hydrolysis
(dephosphorylation)
33
Phosphatidyl inositol system (p. 133)
• Gp protein activates phospholipase C (PL-C)
• PL-C catalyzes the hydrolysis of phosphatidyl inositol bis
phosphate (PIP2):
• PIP2 + H2O  IP3 + DG
• both products (IP3, DG) are second messengers
34
The structure of PIP2
O
C
C
O
O CH2
O CH
CH2
OH
O
O P O
O
OH
O P
HO
O
P
describe the structure
35
Q.
What is the source of inositol in human body?
36
The origine of inositol
HO
OH
HO
OH
HO
OH
Exogenous source: food
Endogenous source: glucose-6-P (side path of metabolism)
37
DG and IP3 as second messengers
• DG activates protein kinase C  phosphorylation of
intracellular proteins
• IP3 opens calcium channel in ER  Ca2+ concentration in
cytoplasm increases  Ca2+ ions are associated with
special protein calmodulin (CM)  Ca2+-CM complex
activates certain types of kinases  biological response
38
Insulin receptor
• has four subunits (α2β2)
• extracellular α-units bind insulin
• intracellular β-units have tyrosine kinase activity 
phosphorylation of tyrosine phenolic hydroxyl of
intracellular proteins including insulin receptor itself
(autophosphorylation)  cascade of further events 
biological response
39
Intracellular receptors:
- cytoplasmatic
- nucleic
for steroids, iodothyronines, calcitriol, retinoids
40
Intracellular receptors
• make complex with hormone
• activate or repress the transcription of genes
hydrophobic hormone penetrates cell membrane
active complex receptor-hormone
active complexes dimerize
are translocated into nucleus
inactive receptor
in cytoplasm in complex with
hsp dimer and other proteins
41
Steroid and thyroid hormones
• insoluble in water  in ECF are transported in complex
with transport proteins
• hormone themselves diffuse easily across cell membrane
• they are bound to cytoplasmatic or nuclear receptors
• in nucleus, the hormone-receptor complex binds to HRE
(hormone response element) in regulation sequence of DNA
• this leads to induction of mRNA synthesis = transcription of
gene
42
Events on synapses
43
Cholinergic synapses
• neurotransmitter: acetylcholine
• two types of receptors
• nicotinic rec. (ion channel) – e.g. neuromuscular junction
• muscarinic rec. (G-prot.) – e.g. smooth muscles
44
Cholinergic receptors
Feature
Nicotinic receptor
Muscarinic receptors
M1, M3
M2
Receptor type
Ion channel
Gp
Gi
2nd messenger
∆ψ*
DAG, IP3
cAMP ↓
Antagonist
tubocurarine
atropine
atropine
Locations
neuromuscular juct.
brain
myocard
* the change of membrane potential
45
Q.
How is acetylcholine released from presynaptic
terminal?
46
A.
• influx of Ca2+ triggers the fusion of presynaptic vesicles
(contaning acetylcholine) with cell membrane and
exocytosis of acetylcholine
• acetylcholine is liberated into synapse
47
Q.
What reaction is catalyzed by acetylcholinesterase?
48
A.
acetylcholine + H2O  choline + acetic acid
hydrolysis of ester
49
Q.
What is nicotine?
50
Nicotine is the main alkaloid of tobacco
(Nicotiana tabacum)
2
3
more basic
1
2
N
less basic
N
pKB = 6.2
CH3
1
pKB = 11
3-(1-methylpyrrolidine-2-yl)pyridine
51
Q.
Why nicotine triggers the release of adrenaline?
52
Main effects of nicotine
• nicotine binds to acetylcholine nicotinic receptors in brain and
other tissues including cells of adrenal medula
• stimulates the secretion of adrenaline – because it binds to
receptors in adrenal medula (p. 135 !) - silent stress
other effects:
• increases the secretion of saliva and gastric juice
• increase intestinal peristalsis
• vasoconstriction
53
Q.
What is muscarine?
54
Muscarine is an alkaloid in some mushrooms
CH3
HO
H3C
CH2
O
N CH3
CH3
HO
CH2
CH2
CH3
muskarin
muscarine
N CH3
CH3
kandicin
tetrahydro-4-hydroxy-N,N,N,5tetramethyl-2-furanmethanammonium
Amanita muscaria (fly agaric)
55
Inhibitors of acetylcholinesterase
• Reversible – carbamates (N-substituted esters of carbamic
acid), e.g. fysostigmine, neostigmine
• they are used to improve muscle tone in people with
myasthenia gravis and routinely in anesthesia at the end of an
operation to reverse the effects of non-depolarising muscle
relaxants. It can also be used for urinary retention resulting
from general anaesthetia
• Irreversible – organophosphates, very toxic compounds
56
Carbamates – General formulas
O
H2N C
O
R
H2N C
OH
O
N C
O R
R
O R
carbamic acid
alkyl carbamate
N-disubstituted
(hypothetic compound)
(ester)
alkyl carbamate
57
Organophosphates
S
HO P OH
OH
thiophosphoric acid
O
HO P F
HO P CN
OH
fluorophosphoric acid
O
O
HO P CH3
HO P CH3
OH
F
kys.
methylfosfonová
methylphosphonic
acid
O
kys.
methylfluorofosfonová
methylfluorophosphonic
acid
OH
cyanophosphoric acid
O
H3C
O P CH3
H3C
F
sarin
58
Adrenergic synapses
• neurotransmitter: noradrenaline
• four types of receptors: α1, α2, β1, β2
• all of them are G-protein linked receptors
• occur in various cells and tissues
59
Adrenergic receptors
Feature
α1
α2
β1
β2
G-protein
Gp
Gi
Gs
Gs
DG, IP3
cAMP
cAMP
cAMP
smooth muscle
brain
myocard
smooth m.
2nd messenger
Occurence*
* Example of occurence
60
Q.
Describe the synthesis of noradrenaline.
61
The formation of DOPA and dopamine
COOH
H2N CH
NH2
COOH
hydroxylation
hydroxylace
CH2
H2N CH
CH2
CH2
dekarboxylace
decarboxylation
CH2
- CO2
O2, BH4
OH
OH
OH
tyrosin
tyrosine
OH
DOPA
DOPA
(3,4-dihydroxyfenylalanin)
3,4-dihydroxyphenylalanine
OH
dopamin
dopamine
(katecholamin)
62
Noradrenaline and adrenaline
NH2
CH2
NH2
hydroxylace na
hydroxylation
at C-2
C2
CH2
O22, ,ascorbate
askorbát
O
NH CH3
N-methylation
N-methylace
CH2
CH OH
SAM
CH2
CH OH
Cu2+
OH
OH
dopamin
dopamine
OH
OH
noradrenalin
noradrenaline
prefix nor- means N-demethyl
OH
OH
adrenalin
adrenaline
63
The next seminar
April 24, 2006
Chapter 21 - I. part
64