Pharmacology I-IV Flashcards
Langley’s experiment : giving rise to idea of receptors
1) pilocarpine added to heart - slows heart rate and increases savliva secretion
2) if atropine added to heart - nothing happened
3) atropine + pilocarpine - pilo didnt slow heart rate
= effects were antagonised by atropine
effects dependant on concentration of poison and affinity for substances
Experiments with nicotine and curare on chicken legs
Action --- Contraction? stimulate nerve --- yes apply nicotine --- yes apply curare and stimulate nerve --- no apply nicotine and curare --- no = SO NICOTINE MIMICS EFFECTS OF STIMULATION, CURARE STOPS BOTH, DOES IT ACT ON NERVE OR MUSCLE?: DENERVATE (kill nerves) apply nicotine --- yes apply curare and nicotine --- yes = SO NICOTINE AND CURARE ARE ACTING ON MUSCLE, STIMULATING NERVES PRODUCES SUBSTANCE THAT MIMICS ACTION OF NICOTINE
Ehrlich’s experiment
on blood cells - found evidence of receptors:
applied dyes to cells and saw different cells absorbed different dyes - selectivley
Macromolecular proteins
serve as recognition sites for neurotramsitters, hormones etc used in cell communication
also refers to any protein of a cell that can bind a molecule/drug, which modulates some activity
Chemical mediator
extracellular signalling molecules e.g. hormones
detected by target cells through receptors
cell signalling occurs when …
receptors detect extra cell signals and genterate intra cell signals = signal transduction
Endocrine communication
long distance
sig mol secreted into blood stream
e.g. adrenaline, insulin
Paracrine communication
locally, signals to neighbouring cells
may be stored in vesicles or synthesised on demand and diffuse across membrane
if cell receiving is same type as cell making it = autocrine
e.g. growth factors : histamine, nitric oxide, anadin, CBD
Neuronal communication
may be long distance, very fast, specific to target cell (synapses)
chemical mediators that diffuse across cleft from vesicles
e.g. botox - interfere with synthesis, storage or release of neurotransmitters; nicotine and curare - act on receptors for neurotransmitters
Contact - dependant communication
shortest range
used in immune system
e.g. T cell receptors interact with receptors on antigen presenting cells to become activated, so they can recognise infected/damaged cells, CAR-T immunotherapy uses contact dependant to kill cancer
Bioassays =
experimental assays, concentration of substances measured by the biological response it produces
Bioassays used to:
measure pharmalogical activity of new substrates
investigate function of endogenous mediators
measure drug toxicity and unwanted effects
Loewi’s experiment - followed on from Langley
if vagus was stimulated, heart rate slowed - what caused this?
if it was a chemical, he should be able to collect it and test it on another heart:
2 isolated hearts, stimulated 1 vagus nerve and collected medium heart was in
put the medium onto 2nd heart and the message transferred - he called it ‘vagustoff’
Dale continued this research on leeches and found the chemical was Ach
Acetylcholine effects on differenct receptors (CNS)
Somatic efferent system = binds to nic receptors and controls skeletal muscle
sympathetic system =
nicotinic - noradrenaline - blood vessels
nicotinic - muscarinic - sweat glands
nicotinic - adrenal medulla
Parasympathetic system = nicotinic - muscarinic - salviary glands
Experimental criteria:
1) released from cells in sufficient amounts to produce bio action on target in appropriate time frame
2) application of authentic sample of mediator reproduces original bio effect
3) interference with synthesis, release or action (e.g. enzyme inhibitors) abalates or modulates original bio effects
Synthesis of small molecules
- regulated by specfic enzymes, peptides synthesis regulated by transcription - which mediator produced depends on which enzymes/gens are active
- some secretory vesicles store more than one type of transmitter
Synthesis, storage and release
2 groups:
1) mediators that are preformed are stored in vesicles then released by exocytosis = allows for rapid communication (microseconds)
2) mediators produced on demand are released by diffusion or constitutive secretion = take longer to act (minutes to hours) e.g. lipids and small gases
in nerve ending, transporter protein loads neurotransmitters into vesicle
vesicle docks at plasma membrane
when signal is generated e.g. action potential, vesicle fuses with membrane creating fusion pore
neurot escapes and goes to receptor on other cells
endocytosis recycles vesicle
Research into mediators
neurot. storage = early studies demonstrated quantal nature of tranmission (hinted at existence of ‘packages’)
developents in microscopy lead to packagess being ideatified as vesicles
cryoelectron microscopy identified protein rquired to dock vesicles at membrane = SNARE proteins
new reaserch investigates molecular mechanisms for regulating release: vesicles involved in exocytosis have calcium sensor proteins = synaptotagmin
Termination of action
transmission needs a process that will rapidly dispose of released neurot
cholinergic synapses - enzyme = acetylcholinesterase
other synapses rely on uptake back into neutron for supporting cells - specific transporters for diff types of neurotransmitters
Pharmacology principles
1) drug action must be explicable in terms of conventional chemical intercations between drug and tissues
2) drug molecules must be ‘bound’ to particular constituents in order to prudce effect
3) drug molecules must exert some chemical influence on one or more constituents of cells to produce a pharmalogical response
Drugs interfere with neurotransmission, used to allevaite neurological conditions
antidepressants - can target transporters, block protein site so neurot isnt disposed of
amphetamines - indirectly increase noradrenaline release ny displacing it from its vesicles
ion channels - e.g. lignocaine, gabapentin
receptors - e.g. opium
Receptors (pharm definition)
protein that binds chemical mediators e.g. hormones, neurot
functions of receptors
regulation of cellular processes
1 - chemical recognition and binding
2 - intracellular signal generation
Classified by structure
4 main classes
‘super families’
same class = common overall structural features
3 classes found on cell surface
STRUCTURE 1) Ligand gated ion channel (ionotropic receptors)
control flow of specific ions across membrane, binding site facing outside, in series with a number of trans membrane domains
STRUCTURE 2) G protein coupled receptor (metabotropic receptors)
all proteins that code for these have 7 transmembrane domains, anchors them into membrane
depending on sub family - binding domains in either amino terminus or ligand binding domain maybe in a ‘pocket’ inside membrane, have conservation in intracellular loops
recognised by and bind G proteins
STRUCTURE 3) kinase - linked receptors
simple, single trans membrane domain, ligand binding site in amino terminus, range of bidning sites, used in immune and hormone signalling, transduction done by kinase being associated with them (phosphorylates other proteins)
STRUCTURE 4) Nuclear receptors
no transmem domains, common drug target, found in cytoplasm or nucleus have DNA binding sites built in, directly control transcription of specific genes, used by lipophilic mediators
agonist
bind to receptor to produce a response e.g. pilocarpine, nicotine, acetylcholine
antagonist
prevent/inhibit response of an agonist e.g. atropine, curare, naloxone
ligand
any molecule that binds to receptor
signal transduction in:
ligand gated ion channel
most rapid
proteins arrange to open pore and ions flow through
milliseconds
e.g. nicotinic ACh receptor
signal transduction in:
G protein coupled receptor
agonist bound receptor, activates G protein whic controls function of other proteins - could be enzymes or ion channels in membrane
seconds
e.g. muscarinic ACh receptor
signal transduction in:
kinase linked receptor
increased / decreased expression of certain genes
hours
e.g. cytokine receptors
signal transduction in:
nuclear receptors
regulate transcription
hours
e.g. oestrogen receptor
Ligand gated ion channels
fast transmission
endogenous (ones we produce ourselves) agonists are fast / classic neurotransmitters, stored in synaptic vesicles e.g. ACh, glutamate, GABA
3-5 subunits
each subunit has 2 - 4 transmembrane domains
complex arrangemnt to form central aqueous pore
agonist binding = channel opening - channel is closed when agonist removed or receptor enters ‘desensitised’ state
ions flowing through open channels produce changes in cell potential e.g
excitatory neurotransmitter = ACh in PNS, glutamate in CNS = mem depolarisation, action potential firing
inhibitory neurot = inhibit mem depol, reduce action potenital firing
sub families of ligand gated ion channels
1) cys-loop (pentameric assembly) e.g. nAChR, GABAR
2) ionotropic glutamate (tetrameric assembly), contain p loop e.g. NMDA
3) P2X (trimeric assembly), contain ATP gated channels, e.g. P2XR
4) calcium release (tetrameric assembly), e.g. IP3R
Nicotinic receptor subtypes (3)
muscle type
ganglion type
CNS type
Muscle type nicotinic receptors
- location
- membrane response
- agonist
- antagonist
- skeletal NMJ post synapse
- excitatory EPP
- ACh, CCh
- alpha-bungarotoxin , tubocurarine
Ganglion type nicotinic receptor
- location
- membrane response
- agonist
- antagonist
- autonomic ganglia, post synapse
- excitatory, EPSP
- ACh, CCh
- trimetaphan
CNS type nicotinic receptor
- location
- membrane response
- agonist
- antagonist
- brain, pre and post
- mainly pre-synaptic
- ACh, DMPP
- mecanylamine
G protein coupled receptors (metabotropic)
receptor formed from single protein
7 transmem domains, heptohelico
heterotrimeric - 3 diff proteins form a G protein
regulate effector proteins
following agonist binding to a GPCR = signal transduction occurs via activation of heterotrimeric G proteins
activated subunit binds guancine triphosphate ( G receptor)
20 types of G protein, diff receptor sub types signal via diff G proteins
same G protein may be used by more than one receptor
3 subunit = alpha, beta, gamma, allow receptor to talk to and regulate effectors
act as switches
GPCR ‘on’
signal molecule activates receptor
alpha contains binding site for nucleotide, forms complex with beta,gamma
agonist bound receptor is in direct contact with alpha subunit using intracellular loops for interaction
receptor binding causes change in alpha subunit = GDP affinity lowers, GTP affinity increases
receptor comes off alpha so alpha separates from beta,gamma
GPCR ‘off’
alpha is bound to GTP
target protein is activated and GTP hydrolysed
alpha subunit now inactive - dissociates from target and reassembles with beta,gamma to reform inactive G protein
G proteinmay extend signal after signal molecule has gone
Subunits :
alpha (a)
knwon for regulating activity if enzymes involved in producing 2nd messengers
e.g. Gs (a) = stimulates, inc adenyl cyclase = inc cAMP
Gi (a) = inhibits, dec adenyl cyclase = dec cAMP
Gq (a) = activate, inc phospholipase C (PLC) = inc IP3 + DAG = inc Ca in cell
Subunits:
beta,gamma (bg)
known for regulating ion channels, reduced action potential firing
e.g. GIRK = potassium channel opened by bg subunit
opiod receptors act via G proteins, inc GIRK and dec Ca = dec pain transmission in CNS
dec cAMP = addiction
Adenyl cyclase
2nd messenger for cAMP, regulates activity of other proteins in sig trans including PKA, EPAC and GREB
PKA = kinase that phosphorylates other proteins, made of regulatory and catalytic subunits, cAMP binds to regulatory subunits so they fall off to free up catalytic subunits to interact with downstream targets
e.g. in cardiac muscle beta 1 receptors are activated by adrenaline = inc cAMP = inc PKA = phosphorylates Ca channel = inc contractility
e.g. PLC activation by GPCRsleads to generation of 2nd messenger IP3 (which diffuses from membrane and releases Ca from ER) and DAG (which stays in plasma membrane and activates protein kinase c)
e.g. smooth muscle contraction stimulated by receptors coupled to Gq and PLC signalling = inc Ca = contraction
