Specific desensitization of actin polymerization of bovine platelets

Polymerization of actin induced by activation of platelets was investigated using deoxyribonuclease I inhibition assay. When platelets were activated with ADP or 5-hydroxytryptamine, actin was polymerized quickly followed by rapid depolymerization to the initial level. Reactivation with the same agonist, however, did not cause the polymerization of actin, though with different agonists actin polymerized quite normally. The mechanism for this agonist-specific desensitization of actin polymerization was investigated by the use of a calcium ionophore A23187. It was suggested that the cause for the desensitization is the inability of platelets to mobilize Ca2+ in response to specific agonist.