Family of cell surface receptors which mediate opiate drug effects on neurons, lymphocytes, macrophages, and other cells; may or may not coincide with neuropeptide receptors; some are G protein coupled to calcium channel inhibition.

(receptors, opioid) Cell membrane proteins that bind opioids and trigger intracellular changes which influence the behavior of cells. The endogenous ligands for opioid receptors in mammals include three families of peptides, the enkephalins, endorphins, and dynorphins. The receptor classes include mu, delta, and kappa receptors. Sigma receptors bind several psychoactive substances, including certain opioids, but their endogenous ligands are not known.