- Classical receptor theory suggests that the response seen will be proportional to the percentage of receptors occupied
- In this situation when the relationship between receptor occupancy and response is linear
- Occupancy is directly proportional to efficacy
- Affinity is directly proportional to potency, with KD = EC50
- If a simple dose-occupancy curve for a full agonist is plotted on the same axes as a dose–response curve they would be identical
- In this situation when the relationship between receptor occupancy and response is linear
- However, this relationship usually does not bear true:
- Receptor Reserves:
- It is often the case that only 5–10% occupancy is needed to produce a full response
- Indicates that ∼90% of receptors are not needed to elicit a maximum response and hence form the receptor reserve
- Results in dose-response response lying to left of the binding curve in full agonist (EC50 less than KD)
- Partial agonism:
- Implied that at a full response can be produced with full receptor occupancy
- For a partial agonist, even at 100% occupancy a full response (similar to the full agonist) cannot be produced
- Spare receptors are not pooled or hidden; they are simply surplus to requirements
- Receptor Reserves:
