Evidence for functional beta-adrenoceptor subtypes in CG-5 breast cancer cells

beta-adrenergic receptors (beta-ARs) were identified in CG-5 breast cancer cells using a radiometric assay. The total beta-AR concentration was measured using the highly potent beta-adrenergic antagonist (-)[H-3]CGP 12177, and the densities of beta-AR subtypes were discriminated in the presence of highly selective unlabelled ligands (CGP 20712A and ICI 118551). Scatchard analysis revealed good linearity (r>0.95) and K-d values (0.05-1 nM) indicated the presence of high affinity binding sites in CG-5 cell membranes. beta(2)-AR concentrations (74%) were significantly (P<0.05) higher than beta(1)-AR concentrations (36%). Displacement studies indicated that tested adrenergic agonists displaced (-)[H-3]CGP 12177 from its specific binding sites in the order of potency (-)isoproterenol>(+/-)clenbuterol>(-)adrenaline>(+/-)dobutamine much greater than>(-)noradrenaline, whereas beta-adrenergic antagonists inhibited the binding in the following order of potency: (-)propranolol much greater than ICI 118 551 much greater than much greater than CGP 20712A. The functionality of beta-ARs identified in CG-5 cell membranes was demonstrated by the significant increase in cAMP production induced by different concentrations of isoproterenol vs unstimulated cells (control). The pathophysiological role of beta-ARs in breast cancer cells is still undefined, but their presence suggests the possible adrenergic regulation of some cellular activities such as proliferation and/or differentiation. (C) 1996 The Italian Pharmacological Society.