Identification and regulation of adrenergic receptors in target cells.

The application of radioligand binding techniques has recently led to increased understanding of adrenergic receptors, the recognition sites for catecholamines on target cells. Radioligand binding is a simple technique to conduct, although data obtained from binding studies are not always as easy to interpret as they are to generate. Nevertheless, the goal of these studies is to help define the molecular physiology of catecholamine action. In this article, I address five principal questions that largely dominate current research on adrenergic receptors. 1) How many types and subtypes of adrenergic receptors exist? 2) What is the structure of adrenergic receptors? 3) How is occupancy of adrenergic receptors translated to changes in target cell response? 4) How do target cells regulate their complement of adrenergic receptors? 5) Do alterations in adrenergic receptors mediate altered pathophysiology in disease? Although only preliminary answers are available, the use of radioligand binding methodology, together with other biochemical, cell biological, immunological, and molecular biological approaches should provide the tools to obtain definitive answers to those questions within the near future.