Delta Receptors
Opioid receptors are specialized “recognition” proteins located on cell membranes in many organs, including the central and peripheral nervous systems. Currently, three opioid receptors, mu, delta, and kappa, have been shown to be important in human physiology. The mu receptor, first identified in 1972, was rapidly understood because of the historical knowledge of classic mu receptor agonists such as morphine, fentanyl, and oxycodone. The delta receptor was identified in the late 1970s. However, without the availability of cloning tools, non-peptide agonists, and other such advanced techniques, detailed knowledge of the function of this receptor was not gained until the early 1990s when our founder, Dr Chang, and his team discovered the first non-peptide delta receptor agonists.
The delta-, mu- and kappa-opioid receptors are similar to each other in protein structure but link to a variety of distinct intracellular G-coupling proteins that function to cause the receptors’ unique physiologic effects on target organs. As members of the superfamily of G-protein coupled seven transmembrane (7-TM) receptors, opioid receptors belong to one of the most important families of drug targets for the pharmaceutical industry.
There is a growing realization that because the opioid receptor/G-protein apparatus produces biochemical reactions that differ from cell to cell, and because these receptors are found in many organ systems, compounds interacting with opioid receptors have far-reaching clinical potential not only in analgesia but in other indications. The role of delta receptors as critical regulators of cellular function in several organ systems is clearly established by the many ion channels and enzymes coupled to these receptors and their associated physiological responses. This diversity, along with the multiple opioid receptor subtypes and specific tissue localization, highlights the potential of selectively targeting this receptor for the discovery of therapeutic agents.