1.3 Receptors Flashcards
(19 cards)
What are the five types of receptor antagonism?
Competitive, irreversible, allosteric, inverse, and functional (physiological) antagonism.
What is a common feature among all antagonists discussed?
They all bind to a target to inhibit receptor-mediated effects.
Where do competitive antagonists bind?
To the same (orthosteric) site as the agonist, reversibly.
What effect do competitive antagonists have on agonist DRC?
Rightward, parallel shifts without reducing maximum response.
What determines agonist vs antagonist binding success?
Relative concentrations and binding affinities.
How do irreversible antagonists bind to receptors?
Covalently (or very slowly reversible) at the orthosteric site.
How do irreversible antagonists affect agonist response?
They reduce the maximum effect by reducing receptor number (RT).
Can you overcome irreversible antagonism with more agonist?
No, because the receptor is permanently inactivated.
Where do allosteric antagonists bind?
At a site distinct from the agonist binding site (allosteric site).
How do allosteric antagonists inhibit receptor activity?
By reducing agonist affinity and/or efficacy through conformational changes.
What is a key property of NAMs’ antagonism?
Dose-dependent but limited due to allosteric site saturation (ceiling effect).
What is constitutive receptor activity?
When unbound receptors exist in an active state and produce effects without agonist.
How do inverse agonists work?
They stabilize the inactive receptor conformation, reducing constitutive activity.
How are inverse agonists different from antagonists?
Inverse agonists reduce basal activity; antagonists block agonist binding without affecting basal activity.
What is functional (physiological) antagonism?
When two agonists at different receptors produce opposing cellular effects.
Example of functional antagonism?
Adrenaline (β₂ agonist) vs Histamine (H₁ agonist) in airway smooth muscle.
Is functional antagonism receptor-specific?
No, it involves different receptors producing opposite actions.
How do antagonists differ by binding site?
Competitive, irreversible, inverse = orthosteric; allosteric = allosteric site; functional = different receptors.
Which antagonists reduce maximal agonist effect?
Irreversible, some allosteric antagonists, and inverse agonists (if constitutive activity is present).
