Direct Identification of Beta-Adrenergic Receptors on Isolated Bovine Parathyroid Cells**

Abstract

The radioiodinated .beta.-blocker iodohydroxybenzylpindolol ([125I]HYP) was used to identify directly and characterize .beta.-adrenergic receptors in isolated bovine parathyroid cells. [125I] HYP was bound rapidly and reversibly to isolated bovine parathyroid cell membranes. Scatchard analysis revealed a single class of binding sites with high affinity (4 .times. 1010M-1) and low capacity (0.7 pmol/mg). Saturation analysis of [125I]HYP binding to intact bovine parathyroid cells suggested a site with similar affinity on whole cells and with a binding capacity of 5000-10,000 sites/cell. True Kd for .beta.-adrenergic agonists and antagonists were in good agreement with activation constants (KA) and inhibition constants (Ki) for effects on adenylate cyclase in membrane preparations. These constants also were in reasonable agreement with KA and Ki previously shown for effects of agonists and antagonists on c[cyclic]AMP accumulation and PTH [parathyroid hormone] release in whole cells. .beta.-adrenergic receptors exist on isolated bovine parathyroid cells, and there is close coupling between receptor binding, effects on cAMP and hormonal release. This represents still another system in which [125I]HYP was successfully used to study .beta.-adrenergic receptors in membrane and intact cell preparations.