mu opiate receptor: cDNA cloning and expression.

mu opiate receptors recognize morphine with high affinity. A 2.1-kb rat brain cDNA whose predicted translation product displays 63% identity with recently described delta and kappa opiate receptor sequences was identified through polymerase chain reaction and cDNA homology approaches. This cDNA recognizes a 10.5-kb mRNA that is expressed in thalamic neurons. COS-cell expression confers naloxonazine-, Na(+)-, and GTP-sensitive binding of mu but not delta or kappa opioid ligands. Expressing cells bind morphine, [D-Ala2,N-methyl-Phe4,glyol5]enkephalin (DAMGO), and [D-Ala2,D-Leu5]enkephalin (DADLE) with nanomolar or subnanomolar affinities, defining a mu opiate receptor that avidly recognizes analgesic and euphoric opiate drugs and opioid peptides.