Short communication

Functional ß-adrenergic receptors in a human mammary cell line (HBL-100)

β-adrenergic receptors (β-ARs) were identified in CG-5 breast cancer cells using a radiometric assay. The total β-AR concentration was measured using the highly potent β-adrenergic antagonist (−)[³H]CGP 12177, and the densities of β-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) andK_dvalues (0.05–1 nM) indicated the presence of high affinity binding sites in CG-5 cell membranes. β₂-AR concentrations (74%) were significantly (P<0.05) higher than β₁-AR concentrations (36%). Displacement studies indicated that tested adrenergic agonists displaced (−)[³H]CGP 12177 from its specific binding sites in the order of potency (−)isoproterenol>(±)clenbuterol>(−)adrenaline>(±)dobutamine⪢>(−)noradrenaline, whereas β-adrenergic antagonists inhibited the binding in the following order of potency: (−)propranolol⪢ICI 118 551⪢⪢CGP 20712A. The functionality of β-ARs identified in CG-5 cell membranes was demonstrated by the significant increase in cAMP production induced by different concentrations of isoproterenolvsunstimulated cells (control). The pathophysiological role of β-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.

AC glioma cells, a clonal cell line derived from a rat glioma, responded to 1 mM dibutyrylcyclic AMP and isobutylmethylxanthine with a change to stellate morphology. A concentration-related morphological change was induced by β₁- and β₂-adrenergic agonists with the order of potency being isoproterenol > soterenol > norepinephrine. Propranolol (nonselective β-antagonist), butoxamine (β₂-antagonist) and metoprolol (β₁-antagonist) significantly decreased the cell response to isoproterenol. Schild analysis of the response, using the competitive antagonist metoprolol, gave pA₂ values of 7.5 and 8.5 for the agonists norepinephrine and soterenol, respectively, with slopes of the curves being less than unity. These observations indicate that both β₁- and β₂-adrenergic receptors mediate the change in cellular morphology.