Inhibition of mast cell adenosine responsiveness by chronic exposure to adenosine receptor agonists

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Mast cell adenosine receptors are up-regulated functionally and numerically by chronic exposure to receptor antagonists, but their response to long-term treatment with receptor agonists has not been studied. To address this issue cultured mouse bone marrow-derived mast cells were exposed to N-ethylcarboxamide adenosine (NECA), an adenosine receptor agonist that augments stimulated mast cell mediator release. Cells grown for 3 days in 1 nM NECA responded normally to A23187 or antigen in releasing β-hexosaminidase, but the ability of exogenous adenosine to potentiate this mediator release was attenuated markedly. This inhibition of adenosine responsiveness was partially present after 10 min of 1 μM NECA exposure and complete after 4 hr. The inhibitory effects could be reversed by washing NECA-exposed cells and returning them to culture for more than 4 hr. The adenosine present in the fetal calf serum coupled with deoxycoformycin attenuated mast cell adenosine responsiveness. The NECA-treated cells also exhibited a hyporesponsiveness to adenosine's augmentation of cell cyclic AMP content. This hyporesponsiveness was specific for adenosine receptors in that exogenous isoproterenol was able to increase cyclic AMP levels to a similar degree in both control and NECA-treated cells. Thus, chronic NECA exposure induces a homologous desensitization of mast cell adenosine receptors.