The effect of amiodarone on the beta-adrenergic receptor is due to a downregulation of receptor protein and not to a receptor-ligand interaction.

• Downregulation of beta adrenergic receptors (beta-AR) by amiodarone (Am) have been reported in several studies both in vivo and in 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 beta-AR or to downregulation of the beta-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 beta-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 beta-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 beta1-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 beta-AR is due to a downregulation of the beta-AR protein and not to a competitive or non-competitive receptor-ligand interaction. This indicates a new pharmacological mechanism for modulation of beta-AR, which probably is transcriptionally regulated.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Fysiologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Physiology (hsv//eng)

Nyckelord

Adenosine Triphosphate

metabolism

Adrenergic beta-Antagonists

pharmacology

toxicity

Amiodarone

pharmacology

toxicity

Animals

Binding Sites

drug effects

Blotting

Western

Down-Regulation

drug effects

Ligands

Mice

Myocardium

Propanolamines

metabolism

Receptors

Adrenergic

beta

metabolism

Signal Transduction

drug effects

Time Factors

Tritium

Tumor Cells

Cultured

Publikations- och innehållstyp

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