C5a stimulus-secretion coupling in rat basophilic leukaemia (RBL-2H3) cells transfected with the human C5a receptor is mediated by pertussis and cholera toxin-sensitive G proteins.

Rat basophilic leukaemia cells (RBL-2H3) were transfected with either the wild type human C5a receptor or a truncated form lacking the last 23 C-terminal residues. Transfected cells bound human C5a specifically, with affinities in the range 3-20nM, and 12-166,000 receptors per cell, similar values to those obtained on human neutrophils and monocytic cells. The stimulation of secretion by human C5a was completely inhibited by pertussis toxin and partially sensitive to cholera toxin, indicating that both wild-type and mutated receptors are coupled to G proteins. Cells transfected with the mutated receptor were equally sensitive to hC5a, suggesting that this portion of the C terminus is not an absolute requirement for signal transduction.