ABSTRACT
Nucleotides are important extracellular signaling molecules. It has been established that nucleotides are released from damaged cells, activated platelets and endothelial cells. Thus, at the site of vascular injury, the concentrations of extracellular nucleotides can become elevated. Nucleotides have been shown to cause mobilization of intracellular calcium, upregulation of Mac-1 (CD11b/CD18), degranulation, and chemotaxis in human neutrophils. The goal of this work is to investigate the functional characteristics of nucleotide-receptors in human neutrophils. Nucleotides (ATP and UTP), caused intracellular calcium mobilization in a dose dependent manner. Pharmacological characterization using selective agonists (ATP, UTP), pertussis toxin in human neutrophils and human astrocytoma cells 1321N1 stably expressing P2Y2 or P2Y4 receptors, revealed that human neutrophils express only functional P2Y2 receptors. Treatment of neutrophils with pertussis toxin causes a partial inhibition of nucleotide-induced calcium mobilization. Similarly, by using 1321N astrocytoma cells expressing the P2Y2 receptor we confirmed that calcium mobilization is only partially inhibited by pertussis toxin. The partial resistance of P2Y2-mediated intracellular calcium mobilization suggests that this receptor subtype is coupled not only to a Gi protein, but also to a protein belonging to the Gq-family (most likely G16). In conclusion, we have shown that human neutrophils express functional P2Y2 receptors and all the nucleotide responses are mediated by P2Y2 receptor subtype and that P2Y2 receptors are the functional able to trigger intracellular signaling event in human neutrophils through dual activation of different G proteins.
