Definition of Receptors in Radioligand-Binding Experiments

The fundamental purpose of radioligand-binding experiments is to study the binding of drugs to receptors. Thus, a key question to be addressed is whether or not the binding site detected in the experiment really corresponds to the receptor of interest. However, the identification of binding sites as receptors is by no means a simple problem and is one that has dogged binding studies from their inception. The essence of the problem is this: the definition of a receptor is functional—drugs bind to receptors and produce a response. However, no response is measured in binding experiments.