(2 S,3 R)TMT- l-Tic-OH is a potent inverse agonist at the human δ-opioid receptor

We examined the pharmacologic effect of β-methyl-2′,6′-dimethyltyrosine- l-tetrahydroisoquinoline-3-carboxylic acid ((2 S,3 R)TMT- l-Tic-OH) on G protein activation in membranes prepared from Chinese Hamster Ovary cells transfected with cDNA of the human δ-opioid receptor. (2 S,3 R)TMT- l-Tic-OH inhibited G protein activation to 58% of basal with an EC 50 of 0.72 nM as determined by [ 35 S ]GTPγS binding. These findings suggest that (2 S,3 R)TMT- l-Tic-OH is a highly potent inverse agonist at the human δ-opioid receptor.