deck_666162 Flashcards
Define ligand
A target which binds to a receptor and causes a response
Define affinity
The degree to which a receptor binds to a ligand
Define efficacy
The ability of a ligand to activate a receptor
Define agonist
Drugs that bind to a receptor and cause a response – have affinity and efficacy
Define antagonists
Drugs that bind to a receptor but do not cause a response– have only affinity and NO efficacy – block the effects of agonists
What is binding determined by?
Affinity
What is activation governed by?
Efficacy
How many receptors does a cell have?
10,000 to 100,000 per cell
Hw can you get information regarding binding of drugs?
Use a radioligand (radioactive version of the ligand)
What is Bmax?
The maximum binding capacity– gives information regarding the number of receptors
What is Kd?
The dissociation constant– is a measure of affinity– the concentration of a ligand required to occupy 50% of the available receptorsThe lower the value, the higher the affinity
Define concentration
Th known concentration of drug at site of actionI.e. in cells or tissues
Define dose
The concentration of a drug at the site of action is unknown E.g. Th dose that you give to a patient related to their weight
What law does binding obey?
Th law of mass action– it is related to the concentrations of the products and the reactants (dynamic equilibrium)
Define potency
A combination of affinity and efficacy– governed by the number of receptors – a measure of the drug needed to produce a biological response
What are agonists?
Drugs that mimic endogenous ligands
Way are antagonists?
Drugs that block endogenous ligands
What is critical in determining drug action?
The concentration of drug molecules around the receptors
What determines the amount of receptors bound to receptors?
Concentration of the ligand
What effect will a drug which has good potency have on the EC50 and dose size?
Good potency = low EC50 = smaller dose needed
What effect will a drug which has bad potency have on the EC50 and dose size?
Bad potency = high EC50 = larger dose needed
What is functional antagonism?
Separate pathways mediate contraction and relaxationE.g. Bronchi constriction and bronchodilation
How do side-effects of drugs come about?
Drugs can interact with adrenoceptors which are present in other areas of the body. E.g. Asthma drugs target B-adrenoceptors which are also present in the heart, causing the heart rate to increase
Define spare receptors
Receptor numbers greater than needed to generate a maximum response