Topic 5 - Pharmacodynamics

Question 1

Explain how drugs act on the main primary drug ion channels

Answer 1

Signal molecule binds as a ligand at a specific site on the receptor. Conformational changes open the channel allowing ions to flow into the cell.

The change in ion concentration within the cell triggers cellular responses

There are different types of channels:

Chemically regulated channels will only open in the presence of a certain chemical

Voltage gated channels will only open within a specific voltage range

Mechanically regulated channels will only open with applied pressure

Question 2

Explain how drugs act on the main primary drug targets: Enzymes

Answer 2

Drugs can inhibit the action of an enzyme to alter the physiological response

There is competitive inhibition where substrate and enzyme compete for the same binding site. Generally is reversible. Normal reaction slowed down or inhibited

There is a non-competitive inhibition where the inhibitor bind in a different site to the substrate. Preventing the activation of the substrate binding site.

Question 3

How many family of receptors are there?

Answer 3

• Type 1: Transmitter-gated ion channels
• Type 2: G-protein-coupled receptors
• Type 3: Kinases-linked receptors
• Type 4: Intracellular receptors

Question 4

Explain how drugs act on the main drug receptors

Answer 4

Drugs that bind to a receptor are called an agonist or antagonist.

Partial agonists are ligands that bind and allow normal action. However their bond formation is to a lesser extent and only reduced responses occur

Competitive (reversible) antagonists compete with the binding of the agonist and their action can be overcome by increasing the concentration of the agonist

Competitive (irreversible) antagonists render the target receptor permanently unavailable for binding of the endogenous agonist

Allosteric modulator binds at the second site and causes conformational change in the shape of the protein receptor molecule. Either causing reduced affinity of the primary agonist or potentiating the effect of the primary agonist.

Question 5

Compare and contrast how drugs act as agonists and antagonists by referring to the drug concentration-response curve

Answer 5

Antagonists bind to the receptor to block access of the ligand and thus diminish the normal response.

In competitive (reversible) antagonists Their action can be overcome by increasing the concentration of the agonist

Question 6

Identify the importance of drug potency and maximal drug efficacy

Answer 6

Having a high efficacy relates to the ability of a drug to produce an effect at a receptor

and potency the relative amount of a drug that has to be present to produce an effect