ABSTRACT
This chapter focuses on the criteria necessary to show that a binding site is a receptor: saturability, specificity, and location. Many drugs act by binding to receptor molecules that are designed to bind a hormone or a neurotransmitter. Equilibrium dialysis depends on having a receptor that is not capable of passing through a dialysis membrane, and a ligand that can pass through. The fundamental limiting factor determining whether a receptor can be detected is different for a filter assay. It is simply the amount of radioactivity that can be collected on the filter. A straight, nonhorizontal line on a Scatchard plot is no guarantee that the binding observed is to the receptor of interest. For neurotransmitter receptors, the physiological response is generally considered to be a change in permeability of the postsynaptic membrane to some ion or ions.
