Characterization of adenosine receptors in bovine chondrocytes and fibroblast-like synoviocytes exposed to low frequency low energy pulsed electromagnetic fields

Objective: The present study describes the presence and binding parameters of the A(1), A(2A), A(2B) and A(3) adenosine receptors in bovine chondrocytes and fibroblast-like synoviocytes. The effect of low frequency low energy pulsed electromagnetic fields (PEMFs) on the adenosine receptor affinity and density was studied. Methods: Saturation, competition binding experiments and Western blotting assays in the absence and in the presence of PEMFs on the adenosine receptors in bovine chondrocytes or fibroblast-like synoviocytes were performed. Thermodynamic analysis of the A(2A) or A(3) binding was studied to investigate the forces driving drug-receptor coupling. In the adenylyl cyclase and proliferation assays the potency of typical high-affinity A(2A) or A(3) agonists in the absence and in the presence of PEMFs was evaluated. Results: Bovine chondrocytes and fibroblast-like synoviocytes expressed all adenosine receptors. PEMFs evoked an up-regulation of A(2A) and A(3) receptors and thermodynamic parameters indicate that adenosine binding is enthalpy and entropy driven. In PEMF-treated cells the potency of typical A(2A) or A(3) agonists on cyclic AMP assays was significantly increased when compared with the untreated cells. PEMFs potentiated the effect of A(2A) or A(3) agonists on cell proliferation in both cell types. Conclusions: PEMFs mediate an up-regulation of A(2A) and A(3) receptors related to an increase of their functional activities in bovine chondrocytes and fibroblast-like synoviocytes. No differences are present in adenosine affinity and in the drug-receptor interactions. Our data could be used as a trigger to future studies addressed to PEMFs and adenosine therapeutic intervention in inflammatory joint diseases. (C) 2007 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.