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

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Abstract
[3H]Dihydroergocryptine ([3H]DHE) was shown to bind to sites in membranes from rat neuroblastoma .times. 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/mg of protein and of high affinity, with an apparent 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 (N-[2-(2,6-dimethoxyphenoxy)ethyl]-2,3-dihydro-1,4-benzodioxin-2-methanamine HCl) was found in the membranes derived from NG 108 cells. This finding 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.