Radioligand binding methods for membrane preparations and intact cells

The radioligand binding assay is a relatively simple but powerful tool for studying G protein-coupled receptors. There are three basic types of radioligand binding experiments: (1) saturation experiments from which the affinity of the radioligand for the receptor and the binding site density can be determined; (2) inhibition experiments from which the affinity of a competing, unlabeled compound for the receptor can be determined; and (3) kinetic experiments from which the forward and reverse rate constants for radioligand binding can be determined. Detailed methods for typical radioligand binding assays for G protein-coupled receptors in membranes and intact cells are presented for these types of experiments. Detailed procedures for analysis of the data obtained from these experiments are also given.