Protease-activated receptor ligands increase cytosolic Ca²⁺ levels in human peripheral monocytes and monocyte-derived macrophages. (A) Monocytes loaded with 2 μM Fura-2 acetoxymethyl ester for 30 minutes were stimulated (arrows) with 10 U/mL thrombin, 100 nM trypsin, 10 nM FMLP, or with 300 μM of each PAR-AP. (B) In desensitization experiments, monocytes were sequentially stimulated either with thrombin (10 U/mL) and PAR1-AP (300 μM) or thrombin (10 U/mL). (C) Macrophages loaded with 2 μM Fura-2 acetoxymethyl ester for 60 minutes were stimulated with thrombin, trypsin, PAR-AP, or FMLP, as indicated. Results of 1 of 3 independent experiments are shown.