CD34⁺ HSCs express functional P2XRs. CD34⁺ cells were loaded with the Ca²⁺ indicator fura-2/AM, as detailed in “Materials and methods,” and then stimulated with nucleotides in a Ca²⁺-containing (A-B) or in a Ca²⁺-free medium (C-D) supplemented with 0.5 mM ethylene glycol tetraacetic acid (EGTA). Nucleotides were added at the concentration of 1 mM. Traces are from a single experiment representative of 5 similar ones. Cells were also pretreated with the P2X inhibitor oATP (600 μM for 2 hours at 37°C), rinsed, and then challenged with 1 mM ATP (E; continuous line (i), ATP; dashed line (ii), oATP + ATP). P2R stimulation induces plasma membrane depolarization (F). Cells were loaded with the fluorescent dye bisoxonol as reported in “Materials and methods” and then challenged with increasing ATP concentrations (trace i, 300 μM; trace ii, 1 mM; trace iii, 3 mM). KCl (arrowhead) was 30 mM. Traces are from a single experiment representative of 5 similar ones.