Characterization of (3H)-spiperone binding to alpha 1-adrenergic receptors in a smooth muscle cell line

Although (3H)-spiperone has been demonstrated to interact at both dopamine (D2) and serotonin (S2) receptors, it remains a popular choice for characterization of the D2-receptor using both in vitro and in vivo and in vivo assay techniques. Using a clonal smooth muscle cell culture line (DDT1 MF-2), which has previously viously been characterized as possessing alpha 1- and beta 2-adrenergic receptors, we have found that (3H)-spiperone also has a significant affinity for alpha 1-adrenergic receptors. Our results are consistent with other literature reports which have suggested that spiperone may interact at alpha 1-receptors and we have characterized this interaction. We have also found an additional, high affinity binding site for spiperone on these cells which may represent a D2 - receptor. Characterization of this high-affinity site has been difficult since it is present in very low density. We conclude that (3H)-spiperone binds with high affinity to at least three known neurotransmitter receptor sites: D2-dopamine, S2-serotoninn and alpha 1-adrenergic. The binding to the alpha 1-adrenergic receptor exhibits stereospecificity and a considerable degree of similarity in pharmacological profile to the D2-dopamine receptor.