[Effect of in vitro serotonin on dopaminergic binding sites in rat striatal membranes]

Influence of serotonin on dopaminergic binding sites investigated on striatum membranes of the rat in vitro Two binding sites could be demonstrated for 3H-apomorphine (3H-APO) as well as for 3H-spiroperidol (3H-SPI) in the used membrane fraction of rat striatum (3H-APO: KD' 0.3 nM, Bmax', 47 fMol/mg protein; KD" 3.5 nM, Bmax" 173 fMol/mg protein. 3H-SPI: KD' 0.08 nM, Bmax', 62 fMol/mg protein; KD" 2 nM, Bmax" 271 fMol/mg protein). After preincubation with serotonin (10 microM, 30 min, 37 degrees C) and washing the membranes twice an increase of the high affinity 3H-APO binding and the low affinity 3H-SPI binding by 64% and 57%, respectively, was shown. This effect of serotonin was counteracted by methiothepin (0.1 microM) in both cases. The results provide evidence for allosteric conformation changes of distinct dopaminergic binding sites which can be triggered by specific serotonin receptors in vitro and may be operative under in vivo conditions.