Binding of Amitriptyline to Adenosine A1 or A2a Receptors Using Radioligand Binding Assay

Background and Objective: Tricyclic antidepressants such as amitriptyline (AMT) may result in life-threatening cardiovascular toxicities. Previous studies showed that AMT-induced cardiovascular toxic effects were prevented/reversed by selective adenosine receptor (AR) antagonists. This study aimed to examine whether AMT mediates its cardiovascular effect through binding to ARs and for this purpose measured the binding affinity of AMT to A(1)-or A(2a)-ARs. Materials and Methods: Membranes expressing the A(1)- or A(2a)-ARs were labeled with their specific radioactive ligands ([H-3]-cyclopentyl-1,3-dipropylxanthine and [H-3]CGS21680, respectively). The displacement of the radioligand binding was determined in the presence of different concentrations of AMT or the selective adenosine receptor antagonists for A(1)-AR and A(2a)-AR, 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX) and [8-(3-Chlorostyryl) caffeine (CSC), respectively. The students t-test was used to compare the differences of two groups. Results: The bound A(2a)-AR radioligand was completely displaced by AMT and the Ki value was calculated [half-maximal inhibitory concentration (IC50): 51.42 +/- 15.87 mu M and Ki: 4.8 +/- 0.11 mu M, p<0.05]. High concentrations of AMT (10(4) and 10(3) M) inhibited radioligand binding to the A(1)-AR, which was nearly 25% (p<0.05). Conclusion: AMT showed significant binding to the A(2a)-AR, which might play an important role in its pharmacological and toxicological effects. Finally, the toxicity of high AMT concentrations may be mediated through the A(1)-AR.