The sigmoidal binding curve used to describe drug-receptor interactions plots drug bound against what?

The sigmoidal binding curve used to describe drug-receptor interactions plots drug bound against what?

• A. Drug bound versus log concentration of agonist.
• B. Time to onset versus drug concentration.
• C. Maximal response versus receptor occupancy.
• D. Receptor density versus concentration.

Answer: (A)

The main idea here is how receptor occupancy relates to the amount of agonist present. The sigmoidal binding curve shows how much drug is bound to receptors as you increase the agonist concentration, with the bound amount on the y-axis and the logarithm of the agonist concentration on the x-axis. Plotting against log concentration spreads out the data so the steep middle portion becomes clear, giving that characteristic S-shape. The middle of the curve corresponds to the concentration that gives half-maximal binding, which is tied to the dissociation constant (Kd) for simple one-site binding. At very low concentrations, binding is minimal; at very high concentrations, most receptors are occupied. The other described relationships don’t capture the standard binding isotherm: time versus concentration describes pharmacokinetics, maximal response versus receptor occupancy relates to effect rather than binding itself, and receptor density versus concentration isn’t the binding curve.

The main idea here is how receptor occupancy relates to the amount of agonist present. The sigmoidal binding curve shows how much drug is bound to receptors as you increase the agonist concentration, with the bound amount on the y-axis and the logarithm of the agonist concentration on the x-axis. Plotting against log concentration spreads out the data so the steep middle portion becomes clear, giving that characteristic S-shape. The middle of the curve corresponds to the concentration that gives half-maximal binding, which is tied to the dissociation constant (Kd) for simple one-site binding.

At very low concentrations, binding is minimal; at very high concentrations, most receptors are occupied. The other described relationships don’t capture the standard binding isotherm: time versus concentration describes pharmacokinetics, maximal response versus receptor occupancy relates to effect rather than binding itself, and receptor density versus concentration isn’t the binding curve.