The Effect of Amiodarone on the β-Adrenergic Receptor Is Due to a Downregulation of Receptor Protein and Not to a Receptor–Ligand Interaction

• Published in: Biochemical and biophysical research communications Vol. 255; no. 2; pp. 515 - 520
• Main Authors: Drvota, V., Häggblad, J., Blange, I., Magnusson, Y., Sylvén, S.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 16-02-1999
• Subjects: Adenosine Triphosphate; Adenosine Triphosphate - metabolism; Adrenergic; Adrenergic beta-Antagonists; Adrenergic beta-Antagonists - pharmacology; Adrenergic beta-Antagonists - toxicity; Amiodarone; Amiodarone - pharmacology; Amiodarone - toxicity; Animals; beta; Binding Sites; Binding Sites - drug effects; Blotting; Blotting, Western; Cultured; Down-Regulation; Down-Regulation - drug effects; drug effects; Fysiologi; Ligands; Medicin och hälsovetenskap; metabolism; Mice; Myocardium; pharmacology; Physiology; Propanolamines; Propanolamines - metabolism; Receptors; Receptors, Adrenergic, beta - metabolism; Signal Transduction; Signal Transduction - drug effects; Time Factors; toxicity; Tritium; Tumor Cells; Tumor Cells, Cultured; Western
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1006/bbrc.1998.0138

Downregulation of beta adrenergic receptors (β-AR) by amiodarone (Am) have been reported in several studies bothin vivoandin vitro.The mechanism underlying the antiadrenergic effect of Am is, however, still unclear. The aim of this study was to characterize whether the antiadrenergic effect of amiodarone is due to binding to the β-AR or to downregulation of the β-AR receptor protein. All experiments were performed on confluent mouse AT-1 cardiomyocytes cultured for 6 days. In acute experiments, equilibrium binding with [3H]-CGP-12177 to β-AR was not directly inhibited by Am and the equilibrium binding constant did not change during prolonged exposure up to 72 hours. After Am exposure for 48 hours β-AR density was decreased by 26% (p<0.005). T3 partially prevented the downregulation elicited by Am (p<0.05). A Western blot analysis with β1-AR antibodies revealed a decreased signal intensity in cells treated with Am for 48 h as compared to control (p<0.05). Isoproterenol-provoked cAMP response did not change after acute exposure to Am. After incubation for 48 hours with Am there was, however, a 20% decrease in cAMP response as compared to control (p<0.05). This study shows that the effect of Am on β-AR is due to a downregulation of the β-AR protein and not to a competitive or non-competitive receptor–ligand interaction. This indicates a new pharmacological mechanism for modulation of β-AR, which probably is transcriptionally regulated.