Overview of Techniques for Direct Measurement of Receptor-Ligand Interactions
Most of the commonly used techniques now available for directly measuring receptor-ligand interactions involve the use of radioisotopes. A preparation that contains receptor sites of interest is incubated with a solution that contains the radiolabeled receptor ligand. Receptors are often membrane incorporated, membrane associated, or in some other particulate form. Cells in culture, tissue slices, tissue homogenates (and membrane fractions isolated from them), and purified receptors incorporated into artificial membranes (liposomes) are some commonly employed membranous preparations for ligand binding studies of receptors. When the receptor is “soluble” more elaborate means of separation of bound from unbound ligand are required. Chromatographic separations and immunochemical precipitation of the receptor or unbound ligand are commonly employed methods. Alternatively, the “soluble” receptor can be trapped in a gel, such as those employed for electrophoresis, and handled like a tissue slice. Ideally, the ligand employed will bind to the receptor with both high affinity and high specificity.