C3a induced activation and stimulus specific reversible desensitization of guinea pig platelets.

C3a and its C-terminal hexapeptide lead to a dose dependent release of biogenic amines and nucleotides stored in platelet's granules. The release reaction can be measured by tritiated serotonin or by ATP, indicated by an ATP specific bioluminescence assay. We tested the capability of C3a to induce aggregation of washed platelets. The recently described phenomenon of low dose, stimulus specific desensitization of platelets to the anaphylatoxic peptides C3a and C5a could be shown by measuring the release reaction as well as the aggregation. Further we could demonstrate the reversibility of the stimulus specific desensitization within 2 to 3 hours. The desensitization was proven to be temperature dependent. The recovery of function was independent of newly synthetized protein and is discussed as the result of receptor-recycling.