3H]Spiroperidol Binding in Rat Striatum: Two High-Affinity Sites of Differing Selectivities |
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Authors: | Anne C. Andorn Michael E. Maguire |
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Affiliation: | Departments of Psychiatry and Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106 |
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Abstract: | [3H]Spiroperidol binding to homogenates of rat striatum is saturable and shows either monophasic or biphasic saturation isotherms under specified conditions. In poorly washed membrane fragment preparations, saturation isotherms of [3H]spiroperidol binding are monophasic, revealing an apparently homogeneous set of sites with KD 0.6 +/- 0.3 nM and density 440 +/- 80 fmol/mg protein. However, equilibrium displacement studies of [3H]spiroperidol binding at this site indicate an alpha-adrenergic component in addition to the previously described dopaminergic component. In thoroughly washed membrane fragment preparations, saturation isotherms are clearly biphasic, showing an additional high-affinity site with an approximate KD of 24 +/- 10 pM and an approximate density of 110 +/- 20 fmol/mg protein at a protein concentration of 2.0 mg/ml. Selectivity at this site appears classically dopaminergic, suggesting that the lower affinity site is the primary source of the alpha-adrenergic component of spiroperidol binding. |
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Keywords: | Spiroperidol α-Adrenergic Dopaminergic Striatum Receptor Receptor heterogeneity |
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