Abstract

The present study describes the effect of low frequency, low energy, pulsing electromagnetic fields (PEMFs) on A2A adenosine receptors in human neutrophils. Saturation experiments performed using a high affinity adenosine antagonist [3H]-ZM 241385 revealed a single class of binding sites in control and in PEMF-treated human neutrophils with similar affinity (KD=1.05+/-0.10 and 1.08+/-0.12 nM, respectively). Furthermore, after 1 h of exposure to PEMFs the receptor density was statistically increased (P<0.01) (Bmax =126+/-10 and 215+/-15 fmol mg-1 protein, respectively). The effect of PEMFs was specific to the A2A adenosine receptors. This effect was also intensity, time and temperature dependent. In the adenylyl cyclase assays the A2A receptor agonists, HE-NECA and NECA, increased cyclic AMP accumulation in untreated human neutrophils with an EC50 value of 43 (40 - 47) and 255 (228 - 284) nM, respectively. The capability of HE-NECA and NECA to stimulate cyclic AMP levels in human neutrophils was increased (P<0.01) after exposure to PEMFs with an EC50 value of 10(8 - 13) and 61(52 - 71) nM, respectively. In the superoxide anion (O2-) production assays HE-NECA and NECA inhibited the generation of O2- in untreated human neutrophils, with an EC50 value of 3.6(3.1 - 4.2) and of 23(20 - 27) nM, respectively. Moreover, in PEMF-treated human neutrophils, the same compounds show an EC50 value of 1.6(1.2 - 2.1) and of 6.0(4.7 - 7.5) nM respectively. These results indicate the presence of significant alterations in the expression and in the functionality of adenosine A2A receptors in human neutrophils treated with PEMFs.