EFFECTS OF ADENOSINE AND ITS ANALOGS ON ACTIN POLYMERIZATION IN HUMANPOLYMORPHONUCLEAR LEUKOCYTES

1. The effects of adenosine and its analogues on actin polymerization in human polymorphonuclear leucocytes (PMN) induced by three different chemotactic stimulants, platelet-activating factor (PAF), N-formyl-me thionyl-leucyl-phenylalanine (FMLP) and an activated fragment of C5 (C 5a) were investigated. 2. Adenosine and its analogues inhibited the ac tin polymerization induced by these three agents in a concentration-de pendent manner and theophylline, a competitive antagonist at adenosine receptors, abolished these inhibitory effects.3. The adenosine analog ue 5'-N-ethylcarboxamideadenosine (NECA) was a more potent inhibitor o f actin polymerization than either L-N6-phenylisopropyladenosine (PIA) or adenosine itself, the rank order of potency of these agonists was characteristic of adenosine A2 receptors. 4. Adenosine deaminase (ADA) abolished the inhibitory effect of adenosine and augmented PAF-induce d actin polymerization. 5. It was concluded that, at physiological con centrations, adenosine inhibits actin polymerization in PMN via activa tion of PMN surface membrane adenosine A2 receptors and thus modulates chemotactic stimulus-induced PMN motility.