[H-3] 7-OH-DPAT IS CAPABLE OF LABELING DOPAMINE D-2 AS WELL AS D-3 RECEPTORS

The binding of [H-3](+)-7-hydroxy-2-(N,N-di-n-propylamino)tetralin ([H-3]7-OH-DPAT) to dopamine D-2 and D-3 receptors expressed in Chinese hamster ovary (CHO) cells was investigated and compared with [H-3]methylspiperone. [H-3]7-OH-DPAT labeled the D-3 receptor in the CHO cells in a guanine nucleotide-insensitive fashion and exhibited a K-d of about 0.5 nM. In the presence of MgCl2. [H-3]7-OH-DPAT was also found to label the D-2 receptor in CHO cells with high affinity (3.6 nM). The binding of [H-3]7-OH-DPAT to the D-2 receptor was sensitive to guanine nucleotides suggesting occupancy of a high affinity G protein-coupled state of the receptor. These results suggest that caution should be exercised when using [H-3]7-OH-DPAT to label the dopamine D-3 receptor in brain tissues.