ICPP Flashcards
Name an amine hormone
NA, adrenaline, dopamine, 5-HT
Out of amine, peptide and steroid hormones, order how long their half lives are
Amine seconds, peptide minutes, steroids hours
Name an amino acid neuroT
Glutamate, glycine, GABA
What are metabotropic receptors?
GPCRs
How do ionotropic Rs carry out their effects?
Ca2+ coupled
Name the alpha protein and effector molecules involved in GPCRs
a1 Gaq activ PLC --> IP3 and DAG a2 Gai inhib AC --> cAMP --> PKA B Gas activ AC --> cAMP --> PKA M1/3 Gaq activ PLC --> IP3 and DAG M2/4 Gai inhib AC --> cAMP --> PKA
Describe the structure of a GPCR
7TM, single polypeptide, N terminus is extracellular and C terminus intracellular
What happens following PLC activation
Has two effectors, IP3 and DAG. IP3 joins to IP3 receptor on SR/ER which causes calcium release. DAG activates PKC which phosphorylates proteins
What happens following AC activation
AC hydrolyses ATP to create cyclic AMP which then activates PKA which phosphorylates proteins
At what stage is there signal amplification in GPCR signalling
AC activates many molecules of cAMP
PKA phosphorylates many proteins
PLC activates two effectors (IP3 and DAG)
DAG phosphorylates many proteins
Name all the calcium transporters/channels in a cell
Plasma membrane: NCX, PMCA Ca out, NOCC Ca in, LGIC Ca in
SR/ER: IP3 Ca out, SERCA Ca in, CICR (ryanodine Rs) Ca out
Which molecules can pass through the lipid bilayer?
Small uncharged polar or any hydrophobic molecules
What determines rate of passive transport?
Permeability coefficient and concentration gradients on each side J=P(C1-C2)
If ∆G is positive, what does this mean about the transport process?
Its active transport! ∆G negative is passive transport
What determines if it will be active or passive transport?
Dependent on concentration ratio and membrane potential
What are the glucose and fructose transporters for both sides?
Glucose SGLT, fructose GLUT5 and then both GLUT2 on basolateral side
Give an example of an ATPase Calcium transporter
PMCA (transports Ca out of cell)
What type of transporter is SGLT?
Cotransporter/symtransporter. Transports Na and glucose into cell
What is mainly responsible for RMP of -70mV?
Passive K+ diffusion out of cell through K+ channels
NOT Na/KATPase, this is only responsible for 5-10mV
Name two antiports
NCX (NaCa), NHE (Na H)
How does NaKATPase drive secondary active transport?
Drives Na out so provides energy for transporters that bring Na in e.g. Na/H or Na/Ca antiports or Na/glucose Na/aa symport
Name primary active, secondary active and facilitated transporters in Calcium
Primary active: PMCA (Na/CaATPase), SERCA
Secondary active: NCX
Facilitated: mitochondrial Ca uniports at high Ca to buffer harmful effects
What is NCX?
3 Na in, one Ca out (can reverse mode of operation if low Ca or high Na
Why do you get reversal of NCX activity in ischemia?
So normally NCX moves 3Na in and 1Ca out, but if ischaemic then NaCaATPase (PMCA) doesn’t work so then Na accumulates in cell so NCX reverses direction
What transporters control cell pH
NHE (Na in H out antiport), AE (HCO3- out, Cl- in)
What do you need to have a membrane potential?
Ion gradients and selective ion channels
What is the nernst equation?
Gives the equilibrium potential for an ion (=where chemical and electrical charges are balance) i.e. the membrane potential where the ion will be in equilibrium
If you increase membrane permeability, you move it closer/further away from its equilibrium potential?
Closer to its equilibrium potential
What is fast synaptic transmission?
Where the R is also an ion channel e.g. Nictonic ACh R that lets sodium in
What are excitatory and inhibitory synapses?
Ligand-gated ion channels
Excitatory causes EPSP (ACh, glutamate, dopamine) and inhibitory cause IPSP (glycine, GABA)
Give examples of slow synaptic transmission
GPCRs, use of intracellular messengers
How can you measure the RMP of a cell?
With a microelectrode
Where does depolarisation initiate an ap?
The axon hillock
What are the ARP and RRP?
Absolute refractory period- another AP cannot be generated as nearly all Na channels are in the inactivated state (they have already let Na in and now are tired)
Relative refractory period- a strong stimulus may generate an AP, Na channels recover from inactivation and less are inactivated
What is the structure of voltage gated Na channel?
Channel is made of one alpha subunit. Has four domains (I,II,III,IV) each with 6 transmembrane alpha helices. The S4 segments in each domain act as a voltage sensory- they are positively charged and following depolarisation initiate a conformational change in the channel and cause the pore to open. The pore is between S5 and S6.
What is the structure of voltage gated K channels?
Similar to voltage gated Na channels except the K channel has 4 alpha subunits. Same as Na channel with S4 voltage sensor and pore between S5 and S6.
How do local anaesthetics such as procaine work?
Block Na channels
In terms of axons, what order do local anaesthetics block them?
1st small myelinated
2nd unmyelinated
3rd large myelinated
What fibres conduct sharp localised pain?
Ad
What fibres conduct diffuse pain? (as well as itch)
C fibres
What theory describes the spread of charge along the axon and causes propagation of the action potential?
Local currents
What is capacitance and what is it a property of?
Ability to store charge, a property of the lipid bilayer
What is membrane resistance?
Relates to the number of open ion channels (high resistance = lots of ion channels closed)
Would would a high capacitance membrane mean for conduction?
Stores lots of charge so membrane charge changes more slowly
What would a high resistance membrane mean for conduction?
Lots of ion channels closed so change in voltage will spread further along the axon
Describe the structure of the myelin sheath
Schwann cell rotates around the axon to make a spiral. It is high resistance so allows current to spread further. Decreases membrane capacitance
What do nodes of ranvier have high concentrations of?
Na channels
What is saltatory conduction?
Conduction of an action potential via action potentials only occuring at nodes of ranvier then “jumping” to the next node due to the myelin sheath (which is high resistance so ap can spread)
Name a demyelinating disease
Multiple sclerosis (stops saltatory conduction)
Myelinated axons have a low/high resistance and a low/high capacitance?
High resistance, low capacitance
What channels are involved in the NMJ
depolarisation triggers opening of Ca channels which trigger neuroT release, ACh binds to nAChR on end plate and causes voltage gated Na influx, this depolarises muscle fibre which then contracts
Does the frequency of APs change amount of Ca entry and neuroT release?
Yes, higher frequency APs = more Ca entry = more neuroT release
Describe the structure of voltage gated Ca channels?
Very similar to Na with 4 domains in a subunit (I,II,III,IV)
Which subunit of Na and Ca voltage gated channels forms the pore?
Alpha subunit
Which activates faster: Na or Ca voltage-gated channels?
Na much faster, Ca are slow
What breaks down ACh?
Acetycholine esterase
How does Ca entry lead to neuroT release?
Enters, binds to vesicle via synaptotagmin, vesicle moves close to membrane, Snare complex makes a fusion pore, neuroT released through pore
What ions does nAChR let through?
Cations, N+ and K+
What is an end plate potential?
Axon action potential –> neuroT release –> depolarisation of motor end plate occurs. This is the end plate potential –> generates action potential in the muscle
Name a disease involving the NMJ
Myasthenia gravis- autoimmune against nAChRs causing profound weakness because end plate potentials are reduced
Why are nAChRs fast acting?
Ligand gated ion channel (unlike GPCRs which have to trigger events)
What are Bmax and Kd?
Bmax is maximum binding capacity and Kd is the drug concentration at 50% of Bmax
Low Kd = ___ affinity
High affinity
What are Emax and EC50?
Emax is maximal response and EC50 is concentration at 50% response i.e. EC50 is potency
What is potency?
Measured by EC50, amount of response generated and depends on affinity and intrinsic efficacy (ability to activate receptor). Receptor number can change potency
If Kd for salbutamol is 20uM for B1 and 1uM for B2, what does this mean?
A bit more selective for B2 than B1 (because B2 Kd is lower = higher affinity)
Potency = ___ + ____
affinity + efficacy
Why do we have spare Rs?
Amplify signal transduction Increase sensitivity (allow responses at low concs of agonist)
What’s the point in partial agonists?
Can function as antagonists in presence of full agonist, can allow a more controlled response, can work in the absence/low presence of ligand
What is IC50?
Concentration of antagonist giving 50% inhibition
Define pharmacodynamics and kinetics
PD- what the drug does to the body
PK- what the body does to drug
What are enteral and parenteral drug routes?
Enteral is via GI (sublingual, rectal, oral)
Parenteral is via anything else (SC,IM,IT,IV)
What are SLCs and what types are there?
SoLute Carriers for charged molecules across GI epithelium for drug absorption. Types are OATs or OCTs. Transport either by facilitated diffusion or secondary active transport
Give factors affecting each of ADME
Absorption: drug lipophilicity, pKa, density of SLC expression, blood flow, GI motility,
Distribution: if lipophilic will cross barriers, albumin binding
Metabolism: in Liver Phase I by CYP450 and Phase II by hepatic enzymes, induction or inhibition of CYP450 by other drugs and genetic variation
Elimination: renal function
Which drugs can passively diffuse across GI?
Lipophilic, weak acids and bases
Describe the route drugs are absorbed through once in gut
Gut –> hepatic portal vein –> liver –> body (or enterohepatic circulation meaning back to gut via bile duct)
Bioavailability =
fraction of a defined dose that reaches a specific body compartment
What is Vd?
Fluid volume needed to contain drug at the same concentration as in the plasma
Bigger d gives more penetration of the V
Higher Vd=
More penetration of interstitial/intracellular fluid compartment
Bigger d = more penetration of V
What is first pass metabolism?
Metabolism occuring before the drug reaches the systemic circulation i.e. first pass metabolism by GI/liver
Phase I and II liver enzymes increase/decrease ionic charge or drugs and why?
Increase ionic charge to enhance renal elimination
Give an example of a CYP genetic polymorphism?
CYP2DR for codeine
What routes of elimination are there?
Renal is main, also lung, bile, breast milk, sweat, tears, saliva, genital secretions
What will carry charged molecules across the PCT for renal excretion?
OATs and OCTs (helped by previous phase I and II metabolism that increased charge)
What is clearance?
Rate of elimination of a drug from the body, made up of hepatic clearance (i.e. metabolism) and renal clearance (excretion)
What are linear kinetics?
Rate of clearance is proportional to drug concentration (i.e. plenty of transporters etc). Will be linear on a log scale but curvy on a concentration scale
What are zero order kinetics?
Rate of clearance reaches a limit of capacity- I have zero tolerance for this! Hyperbolic on a log scale but linear on a concentration scale
Which type of kinetics is more likely to result in toxicity?
Zero order
Most sympathetic post-ganglionic neurones are…
noradrenergic
Muscarinic ACh Rs and all adrenoceptors are what type of R…?
GPCR
What cells in the adrenal medulla innervated by the SNS secrete adrenaline?
Chromaffin cells
Describe effects of parasympathetic ACh and the receptors involved
Bradycardia via M2 at SAN and AVN
Bronchoconstriction via M3 at lungs
Increased GI motility via M3
Increased sweat/saliva/lacrimal M1/M3
Describe effects of sympathetic NA and receptors involved
Tachycardia via B1
Bronchodilation via B2
Vasoconstriction via a1
Pupillary dilation via a1
What are catecholamines?
Adrenaline and NA
Side effects of cholinergics i.e. increased parasympathetic activity?
Bradycardia, bronchoconstriction
SLUDGE: salivation, lacrimation, urination. defecation, GI upset, emesis
Which enzymes within the presynaptic terminal metabolise NA?
MAO and COMT
How many people in each stage of drug development?
Phase 1- 50 healthy volunteers for pharmacokinetics and safety
Phase 2- 200-400 people with target disease for pharmacology
IIa is pilot study for dose finding
IIb measures therapeutic action
Phase 3- 1000-3000 target population longer term safety data, efficacy compared with current treatment, large scale RCT
What might happen after lead identification?
Lead optimisation e.g. increase potency, optimise selectivity, optimise PKs,
When are proof of concept and proof of principle established?
Proof of concept is Phase I/IIa
Proof of principle is Phase IIb/III
Four ethical principles
Justice, autonomy, beneficience, non-maleficience
Describe what happens in CICR
Ca enters myocyte via L-type Ca channels, VOCC and/or LGIC then this Ca influx stimulates ryanodine Rs on the SR so that Ca is then released from the SR
What is a Store Operated Channel? (SOC)
Pumps Ca directly into SER when low
How does a GPCR relate to calcium release from SER/SR?
Gq so activates PLC which activates IP3 and DAG, IP3 binds to IP3R on SR/SER to release Ca
What is different about calcium channels in skeletal muscle?
T tubule VOCCs are physically coupled to ryanodine Rs
After muscle contraction how is resting Ca regained?
SERCA moves Ca back into stores
What buffers excessive Ca in a cell?
Mitochondria
Name the 3 calcium buffers in the cytosol, SR, and SER
Cytosol- calbindin
SR- calreticulin
SER- calsequestrin
What does calmodulin do?
Acts a calcium sensor protein. Binds 4 Ca, changes conformation, binds PMCA and increases PMCA sensitivity to Ca x10
Describe normal compartment fluid volumes
70kg human is 60% water so 42kg. 2/3 intracellular (28k) and 1/3 extracellular (14). Of the 14L, 9L is interstitial and 5L is circulating blood volume, 3L of which is plasma and 2L is RBCs.
How does fibre diameter affect conduction velocity?
Bigger diameter = faster conduction
(A fibres fastest and biggest, B fibres middle, C fibres slowest and smallest). Note A and B are myelinated, C unmyelinated
Roughly what value is the internodal distance (between nodes of ranvier)
100 x external diameter of fibre
What cells form the myelin sheath in the CNS and PNS?
CNS: oligodendrocytes
PNS: Schwann cells
When does myelination occur in development?
Third trimester and first two ish years of life
How does adrenaline increase inotropy?
Binds to Gas, cAMP and then PKA activated, PKA activates VOCC channels to increase intracellular calcium
Equation for oral bioavailability?
F = AUCoral / AUCiV
Bioavailability =
amount reaching systemic circulation / amount administered
Anticholinergic side effects
Constipation, dry mouth, urinary retention
What’s thyrotoxicosis? + signs/symptoms
Excess thyroid hormones
Tachycardia, diarrhoea, weight loss, heat intolerance, sweating, amennorhea, palmar erythema
Name a treatment for hyperthyroidism
Carbimazole- inhibits thyroid peroxidase from iodinating tyrosine residues on thyroglobulin so prevents production of T3 and T4
