The differentiation-dependent expression of purinergic receptors for metaboiicaiiy stable analogues of adenosine and ATP was studied in human mononuclear phagocytes (MNPs). Iigands of these receptors are able to modulate cellular cholesterol metabolism. In addition, the intracellular signal transduction pathways of the purinergic receptor system were examined. ATPyS, the metabolic stable analogue of ATP, was used as a P2ligand, and 2-p-(2-carboxyethyl)phenylethylamino-5′-Ar-ethylcarboxamido adenosine (CGS 21680) and 5′-(JV-ethylcarboxamido)adenosine (NECA) were used as P, Iigands in binding studies. Binding of [$S] ATPyS to MNPs at 4°C revealed saturable low-affinity binding sites with aKdof 868±52 nmol/L and B $ of 73±0.4 pmol per 10* cells in 1-day cultured human MNPs and aKtof 780±30 nmol/L and B ml of 14.0±0.8 pmol per 10′ cells in 7-day cultured human MNPs. The characterization of the P, receptors on 1- and 7-day cultured human MNPs showed that they are expressed only on 7-day cultured human MNPs. The specific binding curve of the adenosine A2receptor agonist [3H]CGS 21680 was biphaslc, with aKuof 33±15 nmol/L and aK& of 90±10 nmol/L and withBmMX, of 0.19±0.06 pmol per 10′ cells and B, $ of 0.41 ±0.09 pmol per 10* cells, whereas NECA did not exhibit specific binding. The typical agonists for probing A, receptor subtypes did not bind to 1- and 7-day cultured human MNPs, indicating that only A2receptors are expressed on 7-day cultured human MNPs. ATPyS enhanced [Ca2+]| in 1- and 7-day cultured human MNPs in a concentration-dependent manner, whereas the Pi Iigands, adenosine and CGS 21680, induced Ca2+flux only in 7-day cultured MNPs. All three drugs increased intracellular cAMP levels in 7-day cultured human MNPs at a concentration of 10~5mol/L, whereas no effect was observed in 1-day cultured human MNPs. The uptake of fluorescently labeled acetylated low-density lipoprotein (LDL) in 7-day cultured human MNPs was inhibited by adenosine, CGS 21680, ATP, and ATPyS. No significant influence of these compounds was measured on the uptake of LDL, acetylated LDL, and high-density lipoprotein, in 1-day cultured MNPs. Our investigations indicate that the expression of P2jand A2receptors is increased during differentiation of blood monocytes to macrophages. It is shown that both purinergic Iigands, ATPyS and CGS 21680, inhibit the uptake of acetylated LDL in a concentration-dependent manner, which might impair foam cell formation.