Characterization of (³H)-Spiperone Binding to Alpha₁ - Adrenergic Receptors in a Smooth Muscle Cell Line

Abstract

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 assay techniques. Using a clonal smooth muscle cell culture line (DDT₁ MF-₂), which has previously viously been characterized as possessing α₁- and β₂-adrenergic receptors, we have found that (³H)-spiperone also has a significant affinity for α₁-adrenergic receptors. Our results are consistent with other literature reports which have suggested that spiperone may interact at α₁-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 α₁-adrenergic. The binding to the α₁-adrenergic receptor exhibits stereospecificity and a considerable degree of similarity in pharmacological profile to the D₂-dopamine receptor.