Eighty thousand β-adrenoreceptors in a single cell

CATECHOLAMINES function as hormones in peripheral organs and as neurotransmitters in the central nervous system (CNS). The primary event in the action of catecholamines is their interaction with specific α- adrenoreceptors or β-adrenoreceptors¹. The interaction of catecholamines with β-adrenoreceptors induces the activation of the enzyme adenylate cyclase which converts adenosine triphosphate (ATP) to cyclic AMP (ref. 2). Development of reliable radioligand binding methods has enabled the direct determination of the number of β-adrenoreceptors in various cell types^3-12. The content of β-adrenoreceptors in all the cells examined varies between a few hundred and a few thousand receptors per cell. These values correspond to (0.2-2.0) × 10^-12 mol receptor per mg membrane protein, when membranes are prepared from these cells.