Fig. 3.

Binding and function of C3aR ligands on HEK293 and HMDM cells. a C3aR-binding affinities of hC3a and hC3a-desArg measured by competition with [Eu DTPA]-hC3a (2 nM) on human HEK293 cells transfected with C3aR (C3aR^+/+); b western blot showing no human C3aR expression, and fluorescence plots showing no intracellular Ca²⁺ release induced by C3a, 3 or 6 (vs. positive control: calcimycin) in wild-type human HEK293 cells (C3aR^−/−); c Intracellular Ca²⁺ release induced by C3a or 3 alone or in the presence of 6 (pre-treated 30 min before adding C3a or 3) in human HEK293 cells transfected with C3aR (C3aR^+/+); d Concentration dependent iCa²⁺ release induced by agonist 3 in the presence of 0–1000 nM antagonist 6 (pre-treated 30 min before adding agonist), relative to 100% response for 100 µM 3 on HMDMs. All the data in a–d, n ≥ 3, error bars ± SEM. e, f Metabolic stability for agonist 3 and antagonist 6 vs hC3a in e rat plasma over 4 h and f rat liver microsomes over 1 h, illustrating greater stability of 3 and 6 over hC3a