Drug Receptor Interactions Flashcards
What is meant by a drug
A chemical substance that interacts with a biological system to produce a physiological effect.
List the different drug target sites
Receptors
Ion channels
Transport systems
Enzymes
What do the drug target sites all have in common
They are all proteins
How do drugs essentially illicit their response
By interacting with the drug target site
Summarise tolerance
Tolerance is the measured effect of repeated administration.
Doesn’t occur with all drugs
Limits the use of the drug
Where can receptors be found
Extracellularly (non-steroid)
Intracellularly (steroid)
Summarise receptors
Proteins within cell membranes (usually)
Activated by NT or hormone
Defined by agonists & antagonists
4 types of receptors
What are the 4 types of receptor
Ionotropic
GPCR
Enzyme-linked
Intracellular
What is each drug receptor defined by
By selective agonists and selective antagonists
e.g a compound that selectively stimulates dopamine receptors and not 5-HT or NA receptors
What are families of receptors defined by
By their structures and transduction systems used
What is meant by agonists and antagonists
Agonist- compound that stimulates the receptor
Antagonist- compound that blocks or inhibits the receptor
Give some examples of drugs that act on receptors
Acetylcholine (agonist for acetylcholine receptors)
Atropine (selective antagonist for muscarinic acetylcholine receptors)
What is atropine used for
pre-med before surgery- dry up secretions- particualry bronchial secretions
used to treat cardiac arrest, sinus bradycardia after myocardial infarction
side effects include dry mouth, dilated pupil, bronchodilatation, urinary retention
What is meant by an ion channel
Selective pores - allow transfer of ions down electrochemical gradients
What are the two types of ion channel
2 types 1) voltage-sensitive e.g. VSCC
2) receptor-linked e.g. nAChR
How are ion channels defined
By the gated mechanisms that they use
Describe receptor-linked ion channels
When Ach stimulates the nicotinic receptor- it changes its conformation opening a linked cation channel- allowing a current of Na+ to move into the cell- depolarising the cell- increasing the firing rate of the cell
What is important to remember about nicotinic receptors
They are excitatory
Describe how local anaesthetics work
Lots of action potentials generated in the wound by nociceptive receptors- which sends APs down sensory neurone to the sensory cortex via the thalamus- triggering pain
LAs (e.g lidocaine) get inside the Na+ channel and stereochemically inhibit it (preventing the influx of Na+ ions)- fewer APs- ‘numbing’ the pain
How are local anaesthetics administered
sub-cutaneous
How can calcium channel blockers be used to treat arrhythmias
ClassIV drugs (verapamil) block L-type Ca2+ channels, thereby decreasing the gradient of the pacemaker potential, slowing the rate of depolarisation in the SA node and prolonging the conduction delay in the AV node. They also have negative ionotropic effects by limiting the influx of Ca2+ during the plateau phase
What else can CCBs be used to treat
Hypertension- all blood vessels have sympathetic tone- CCBs prevent influx of Ca2+- reduced contraction of SM-dilation of the vessels- lowering BP
Can also be used to treat angina
What is meant by transport systems
Transport against the conc gradient- need ATP to function
glucose, ions, NTs
Summarise transport systems
Transport against concentration gradients (glucose, ions, NTs)
Specificity for certain species
Examples :Na+/K+-ATPase
: NA ‘uptake 1’
Give some examples of drugs that target transport systems
Tricyclic Anti-depressants (TCAs).
Cardiac glycosides.
What does each NT have
its own specific transporter system
e.g NA uptake 1 only found in NA nerve terminals
Describe tricyclic anti-depressants
Interfere with the function of NA uptake 1 protein
In clinical depression, the NA transport system is not functioning optimally in the CNS
TCAs slow down the uptake system of NA- so more remains in the synaptic cleft for longer enhancing NA.
Also enhances the activity of 5-HT- aiding in reducing the effects of depression.
Describe cardiac glycosides
Glycosides e.g digoxin have a central effect, stimulating the vagus nerve and increasing parasympathetic stimulation, thus slowing heart rate. It simultaneously exerts its positive inotropic effect by inhibition of Na+/K+ ATPase.
Inhibiting Na+/K+ ATPase increases the intracellular Na+, which increases I.C Ca2+- improving contractility.