The human chemoattractant complement C5a receptor inhibits cyclic AMP accumulation through Gi and Gz proteins.

The human C5a receptor is known to signal through Gi proteins. The ability of the cloned C5a receptor to inhibit adenylyl cyclase or to stimulate phospholipase C through Gi proteins was examined in transfected cells. Activation of recombinant C5a receptors resulted in the stimulation of phospholipase C in Ltk- cells and inhibition of adenylyl cyclase in 293 cells. Pertussis toxin potently abolished both responses indicating the involvement of Gi proteins. Previous studies have shown that Gi-mediated inhibition of adenylyl cyclase can be similarly regulated by the pertussis toxin-insensitive GZ. In 293 cells co-transfected with the alpha subunit of GZ, the C5a-mediated inhibition of cAMP accumulation became pertussis toxin-resistant, signifying functional coupling between the C5a receptor and GZ. However, GZ cannot substitute for Gi in the C5a-induced stimulation of phospholipase C or inhibition of adenylyl cyclase in Ltk- cells.