pThe stimulation of reactive oxygen metabolite production from human polymorphonuclear leucocytes by chemotactic peptide (fMet-Leu-Phe) was inhibited by adenosine with a K0.5 of 0.6 microM. Dipyridamole (0.1 microM), an inhibitor of adenosine uptake, did not prevent the effect of adenosine. Non-metabolizable analogues could substitute for adenosine in the potency order N-ethoxycarboxamideadenosine greater than 2-chloroadenosine greater than adenosine greater than L-N6-(phenylisopropyl)adenosine = D-N6-(phenylisopropyl)adenosine, which is characteristic of an A2 adenosine receptor. The effects of adenosine, 2-chloroadenosine and N-ethoxycarboxamideadenosine were reversed by 8-phenyltheophylline. When endocytosis was inhibited with cytochalasin B, cells were still susceptible to adenosine receptor agonists. 2-Chloroadenosine (10 microM) reduced the activation of respiration in response to chemotactic peptide from 3.3-fold to 1.4-fold. Activation of reactive oxygen metabolite production in response to latex beads was not reversed by adenosine or its analogues. It was concluded that adenosine acts at an A2 adenosine receptor to antagonize the activation of polymorphonuclear leucocytes by those stimuli, such as chemotactic peptide, which cause an increase in the intracellular free Ca2+ concentration./p
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