CHARACTERIZATION OF C3A ANAPHYLATOXIN RECEPTOR ON GUINEA-PIG MACROPHAGES

We have characterized a C3a receptor on guinea-pig macrophages by I-12 5-C3a binding and functional responses. Scatchard analysis applied to the I-125-C3a binding to guinea-pig macrophages revealed the existence of two receptor classes; a high-affinity class with approximately 0.6 3 x 10(5) binding sites/cell with a K(d) = 2.7 nM, and a relatively lo w-affinity class with approximately 1.2 x 10(5) binding sites/cell wit h a K(d) = 51 nm. The binding of C3a to macrophages was totally blocke d when there was an excess of C3a. C3a triggered a transient intracell ular Ca2+ ([Ca2+]i) mobilization in macrophages, which was accompanied by homologous desensitization. C3a was also capable of generating O2- from macrophages. The C3a-induced Ca2+ response and O2- generation we re not detected in the pertussis toxin-treated macrophages, suggesting that G proteins are coupled with the C3a receptors of macrophages. Al though the C3a-induced O2- generation was inhibited by staurosporine, it was more resistant to staurosporine than phorbol 12-myristate-13-ac etate (PMA)-induced O2 generation, suggesting that a protein kinase di stinct from protein kinase C may be associated with the C3a receptor.