Characterization by [3H]Dihydroergocryptine Binding of Alpha-Adrenergic Receptors in Neuroblastoma × Glioma Hybrid Cells

3H]Dihydroergocryptine (3H]DHE) was shown to bind to sites in membranes from neuroblastoma X glioma hybrid cells (NG 108-15) that had the characteristics expected of alpha-adrenergic receptors. The binding was saturable with 0.3 pmol 3H]DHE bound per mg of protein and of high affinity, with an apparent dissociation constant (KD) of 1.8 nM. The specificity of the binding site for various ligands was more similar to that of alpha 2 receptors than to that of alpha 1. No specific binding of 3H]WB-4101 was found in the membranes derived from NG 108 cells. This finding also indicated that the 3H]DHE binding site in the cell is the alpha 2 receptor. GTP lowered the affinity of agonists for the 3H]DHE binding site, although the nucleotide hardly affected the affinity of antagonists including 3H]DHE.