Inhibition of PLC abrogates fMLP- and SDF-1–induced LDV-FITC binding in U937-FPR cells. (A) Flow cytometry was used to determine LDV-FITC binding in real time to U937-FPR cells stimulated with 0.5 mM Mn²⁺, fMLP, SDF-1, or buffer (at time 0). One of 3 independent experiments is shown. (B) Free intracellular calcium levels were measured by fluorimetry in Fura2-loaded U937-FPR cells pretreated with DMSO or U73122 and stimulated with fMLP (100 nM), SDF-1 (12.5 nM), thapsigargin (1 μM), or buffer. One of 3 independent experiments is shown. A U73122 dose response is shown in the right panel. Data are expressed as ratios of the peak fMLP-induced calcium flux in cells treated with varying concentrations of U73122 relative to DMSO-treated cells. (C) Flow cytometry was used to determine LDV-FITC binding in real time to U937-FPR cells pretreated with DMSO (0.1%, vehicle control) or U73122 prior to addition of fMLP, SDF-1, Mn²⁺, or buffer at time 0. One of at least 4 independent experiments is shown.