Binding and functional characterization of A3 adenosine receptors in human neutrophils exposed to electromagnetic fields

摘要

Adenosine mediates a number of physiological functions through the interaction with 4 cell surface subtypes classified as A_1, A_(2A), A_(2B) and A_3 receptors which are coupled to G proteins. Recently we have demonstrated that anti-inflammatory actions of adenosine are produced by the involvement of AM and A_3 adenosine receptor subtypes. In human neutrophils A5 receptors exert their anti-inflammatory properties by inhibiting degranulation, chemotaxis and superoxide anion production. Several works have investigated the dependence of prolonged exposure to pulsing electromagnetic fields (PEMFs) on proliferative effects and on cell density. The present paper describes a significant alteration of A_3 adenosine receptor density and functionality in human neutrophils exposed to PEMFs. Saturation binding experiments were performed using a high affinity radioligand antagonist, [~3H]-MRE 3008F20, and revealed a significant increase of A_3 adenosine receptor density in PEMF-treat-ed human neutrophils. A thermodynamic analysis of [~3H]-MRE 3008F20 binding was performed with the aim of obtaining new insights into the effect of PEMFs on the forces driving drug-receptor coupling. Competition of radio ligand binding by the high affinity A_3 receptor agonists Cl-IB-MECA and IB-MECA in the absence and hi the presence of PEMFs has been performed. In functional assays the effects of Cl-IB-MECA and IB-MECA in the adenylyl cyclase activity, in the superoxide anion production and in calcium release have been evaluated.