Demonstration of High‐Affinity Binding Sites for C3a Anaphylatoxin on Guinea‐Pig Platelets

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Abstract
3H‐serotonin release from guinea‐pig platelets was demonstrated to be the consequence of C3a binding to these cells. A Scatchard analysis of dose‐response data of the 125I‐C3a binding pattern to guinea‐pig platelets pointed to the existence of binding sites with high and low affinity for the C3a molecule (HA and LA receptors). HA receptors are specific for C3a with intact C‐terminal arginine. whereas C3adesarg only interacts with LA receptors. The release of serotonin may be induced by a combined reaction of C3a with HA receptors and LA receptors on the platelet membrane.