Autonomic, Cardiovascular, and Central Nervous System Pharmacology EXAM 1

# of transmembrane domains of GPCR

7

t/f most GPCRs are drugged already

false

# of GPCRs

about 800

# of orphan GPCRs

about 150

orphan GPCR

GPCR whose endogenous ligand is unknown

5 GPCR classes

- Rhodopsin (class A)

- Secretin and Adhesion (class B)

- Glutamate (class C)

- Frizzled/taste receptor 2 (TAS2)

examples of physiology that GPCRs regulate

Motor control, Working memory, Mood, Perception, Platelet aggregation, Gastric motility, Insulin secretion, Respiration, Vasoconstriction, Heart rate, Itch, Appetite regulation, Vision, smell, wakefullness

how much of all approved medications target GPCRs

and their biochemical pathways

about 35%

GPCR Structure

-Extracellular NH2 terminus, Intracellular C-terminus, 7 alpha helices

-Intracellular loops interact with heterotrimeric G proteins/effectors

-GPCR ligand/drug binding sites are highly diverse in EC loops and TM domains

GPCR Basic structure

7 Transmembrane Domains (TMDs), 3 intracellular loops, 3 extracellular loops, N- and C-terminals

GPCR Functions

Transduce extracellular transmitter/hormone signals into

cellular/biochemical/physiological responses

Heterotrimeric G proteins

Contain 3 subunits (alpha, beta, gamma) and function with G-protein Coupled Receptors (GPRCs) to transduce signals.

signaling cascade overview (in neurons)

signal molecule -> GPCR -> G protein -> second messenger generation -> modulate ion channel function -> neuron excitability

t/f GPCRs can act to modulate other effectors and not just ion channels

true. enzymes for example

beta arresting interact with GPCR and do what?

block G-protein binding, turn off signaling.

also can modulate receptor trafficking (endo/exocytosis)

also interact with enzymes

active state/conformation of G protein

bound to GTP

inactive state/conformation of G protein

bound to GDP

G protein subunit G alpha

GTPase. cleaves GTP to GDP and turns off G protein signal

there are many subtypes of each G protein monomer

over 1200 alpha beta gamma combos

Gs coupled receptor

excitatory (by activation of adenylyl cyclase, cAMP, and PKA)

Gs coupled receptor in neurons responds to what

norepinephrine

Gq

excitatory (by phospholipase C and Ca2+)

Gi/o

inhibitory (turns of cAMP)

Gq coupled receptor in neurons responds to what

glutamate

Gi/o coupled receptor in neurons responds to what

dopamine or GABA

signal cascade amplification

1 ligand -> 1 receptor on -> 1 adenylyl cyclase -> many cAMP -> 1 kinase on each -> many phosphorylated proteins

what % of receptors need to be activated by agonist for signal effect max

8-10%

what % of receptors need to be blocked by antagonist for full turn off

about 85%

Signaling to the nucleus to regulate gene expression

GPCR/cAMP/PKA signaling to phosphorylate CREB

CRE

cyclic AMP response element

role of CRE

cAMP hits them, they directly change genomic expression in long-term manner.

role in neuroplasticity, learning.

if CRE does long term change, how do you see short term change in neurons?

rapid neuron excitability change by ion channel modification

beta arrestin receptor trafficking summary

induce endocytosis to turn of signal:

sucked up receptors can be ubquinated to be destroyed (long term down regulation)

OR

receptors can be held internally, but sent back out (recycling)

tachyphylaxis

rapid decrease in response to the drug.

"Acute tolerance"

caused by internalized receptors

endosome role in drug clearance

internalized receptors enter low pH endosome, undergo conformational change, and let go of any bound drug

why does internalizing a receptor stop/reduce drug response

the receptor is no longer available for a ligand to bind to it

Desensitization/resensitization

a decrease in responsiveness during continuous drug application or a right-shift in a drug dose-response curve.

After removal of the drug, receptor activity recovers, although the speed and extent of this resensitization can depend on the duration of agonist activation

short term desensitization (rapid)

results from receptor phosphorylation, arrestin binding, and receptor internalization.

Long-term desensitization (down-regulation)

involve changes in receptor and/or G protein levels, and their mRNA stability and expression.

t/f Long-term changes in GPCRs and accessory proteins are known to be induced by chronic drug treatment and involved in several pathologies.

trve...

efficacy

How well the drug causes a conformational change in the receptor to activate G proteins or arrestins

binding affinity

drug-receptor interaction strength

Indicated by the Kd and most commonly Ki

HERG channel in heart

major off-target concern for drugs. inhibition of it can prolong QT interval and cause heart failure

Kd (Dissociation constant)

Concentration at which half the drug dissociates from the receptors (1/2 maximal binding constant)

Ki (inhibitor dissociation constant)

Concentration that competes half of the radiolabeled drug off receptor

Ki =

IC50/(1 + [hot ligand]/Kd hot ligand)

high affinity for Drugs

<50nM

basal (constitutive) activity

receptor flops around and hits active conformation, binds G protein even if no signaling molecule. signaling rate low but on at all times

orthosteric drug

bind to the primary agonist site on a receptor

allosteric modulator

binds to protein away from binding site and changes activity

Drug potency

EC50, drug concentration enabling half maximal response

Drug efficacy

Emax, maximal response of the drug

full agonist

Ability of a drug to produce 100% of the maximum response regardless of the potency

partial agonist

a drug that binds to a receptor and causes a response that is less than that caused by a full agonist

neutral antagonist

stops action at the receptor. sits there and blocks signaling molecules from interacting

inverse agonist

a substance that binds to a receptor and causes it to do the opposite of what the naturally occurring transmitter does

What underlies GPCR inverse agonism?

Inverse agonism is thought to occur by reducing GPCR constitutive activity

Functional selectivity (ligand bias)

The ligand-dependent selectivity for certain signal transduction pathways in one and the same receptor

Different drugs can promote distinct receptor conformations that engage different G proteins (or arrestins) resulting in activation of distinct signaling pathways

SBDD

Structure Based Drug Design based on co-crystal structures

t/f more GPCRs in nervous system than ligand gated neurotransmitter receptors

true

GPCR role in neurons

modulate inhibition/excitation of neurons by altering membrane potential

major excitatory neurotransmitter

glutamate

major inhibitory neurotransmitter

GABA (gamma-aminobutyric acid)

Action potential summary

- -70 mV resting membrane potential, Ion channels are closed

-Stimulus causes depolarization to threshold (-55 mV)

-Na channels open, Na moves into cell = depolarization

-Action potential propagates along cell

-Na channels close

-K channels open

-K moves out of cell (into ECF) = repolarization

-K channels close

-Na/K pump restores ion concentrations

result: Ca2+ channels open in axon terminal and then vesicles with NTs are fused to membrane, dumping cargo into cleft

NTs bind post synaptic neuron receptors and do what?

change their excitability (by direct receptor- ion channel interactions or indirect)

fast synaptic transmission (ionotropic)

Postsynaptic receptor is a transmitter-gated ion channel

Ion channels much more rapid than GPCRs/G proteins

Rate limiting step is time of diffusion (2-5msec)

slow synaptic transmission (metabotropic)

Use of metabotropic G protein-coupled receptors.

1. NTs binds to G protein-coupled receptor.

2. G protein is activated.

3. Activated G protein subunit moves to adjacent ion channel.

4. Ions flow across membrane for longer period of time.

metabotropic changes

GPCR tunes ion channel conductance via phosphorylation or protein-protein interaction. slow modification of excitability of neuron.

location of Na+ channels

axon hillock (and nodes of Ranvier).

GPCRs tune conductance before hillock to modulate excitation

autoreceptors

receptors on presynaptic neuron that respond to the released transmitter by inhibiting further synthesis and release.

inhibitory self-regulation

autoreceptor inhibitory self-regulation example

noradrenaline can reduce Ca2+ permeability of presynaptic neuron, reducing NT release or reducing cAMP expression

through Gi/o activation

opening of K+ channels in neuron

hyperpolarizes neuron, inhibitory. K+ ions leave cell, mem potential decreases, APs turned off

autoreceptors and K+ channels

Gi/o opens K+ channels to inhibit neuron

CNS

central nervous system; brain and spinal cord

PNS

peripheral nervous system

peripheral nervous system subdivision

somatic nervous system and autonomic nervous system

somatic nervous system

the division of the peripheral nervous system that controls the body's skeletal muscles. voluntary movement

autonomic nervous system (ANS)

A subdivision of the peripheral nervous system. Controls involuntary activity of visceral muscles and internal organs and glands.

autonomic nervous system (ANS) further subdivisions

sympathetic and parasympathetic

sympathetic nervous system

fight or flight

parasympathetic nervous system

rest and digest

t/f parasympathetic is anabolic

true. stores energy

symp is adrenergic and uses energy

sympathetic effect in heart and gut

Heart rate increase, gastrointestinal movement decrease

frontal lobe of cerebral cortex

Executive function, impulse control, long-term planning (pre-frontal cortex), motor function (primary motor cortex), speech production (Broca's area)

limbic lobe

emotion

hypothalamus

mater regulator for hormone secretion and controller of autonomic NS

afferent

sensory info goes toward CNS

efferent

motor commands go away from CNS

ANESTHESIOLOGY and autonomic NS

anesthetics negate autonomic NS function

ganglia

bunches of nerves

anatomy of parasymp

preganglionic cell bodies in brain stem and sacral spinal cord.

long myelinated axons to ganglia in target body tissue. few branches

post synaptic fibers are short and unmyelinated and release Ach

t/f all NTs in parasymp are Ach

yeah

anatomy of symp

short pregang fibers by spinal cord release AcH. many branches.

Long post gang fibers then dump norep into target tissue

The ratio of pre- to post- ganglionic fibers in symp

1:20

large magnification of signal

The ratio of pre- to post- ganglionic fibers parasymp

close to 1:1

symp role in epinephrine secretion

symp stimulates adrenal glands (on top of kidneys) to release norep and ep. responsible for about 75% of ep in circulation. rapid mobilization of energy

Describe the autonomic nervous control of a person's bladder in a stressful situation

Under stressful situations, SNS plays a dominate role, and PNS activity is decreased; SNS on detrusor causes relaxation (beta 2) and on internal sphincter (Alpha1, contraction) stops out flow of urine;

At same time, PNS decrease its activity and causes less contraction of detrusor (relaxation, M receptor); Overall, urine is kept in the bladder.

symp and ion channels

uses fast transducing ligand gated ion channels for rapid change

parasym and ion channels

uses metabotropic muscarinic GPRCs and ionotropic nicotinic channels

Choline synaptic transmission

choline enters presynaptic neuron via CHT transporter.

ChAT enzyme makes Ach.

VAT transports Ach into vesicles (which then fuse to membrane and exocytoses Ach when AP/Ca2+ signal arrives).

Hit nicotinic and muscarinic receptors.

Ach degraded by acetylcholinesterase in cleft to turn off signal