NK cells express functional P2Rs. (A) Expression profile of mRNA encoding P2XR and P2YR and the housekeeping gene β2 microglobulin (β2-M) in freshly isolated NK cells, 1 representative experiment of 4 is shown. (B,D) Calcium signal in NK cells stimulated with extracellular nucleotides. Cells were stimulated with 1mM ATP (B) or 300μM BzATP (D) in the presence (continuous line) or absence (dashed line) of extracellular Ca²⁺. For Ca²⁺-free conditions, 0.5mM ethyleneglycoltetraacetic acid was added to the Ca²⁺-free saline solution to chelate contaminating Ca²⁺. Dose-dependency curves for ATP- (C) or BzATP-induced (E) Ca²⁺ response are shown. (F) NK cells were incubated in the presence of the following P2 antagonists/inhibitors: KN62 (100nM, for 30 minutes), PPADS (100μM, for 2 hours), and oATP (600μM for 1.5 hours). Cells were rinsed (oATP and PPADS) and stimulated with 300μM BzATP. One representative experiment of at least 5 similar is shown (B,D,F). Data are mean ± SD of at least 4 independent experiments (C,E).