[35S]GTPγS autoradiography reveals a wide distribution of Gi/o‐linked ADP receptors in the nervous system: close similarities with the platelet P2YADP receptor

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Abstract
No Gi-linked P2Y receptors have been cloned to date but the presence of such receptors is thought to be restricted to platelets and certain clonal cell lines. Using the functional approach of [35S]guanosine 5′-[γ-thio]-triphosphate autoradiography, we uncovered the widespread presence of such receptors in the CNS. Under conditions in which the prominent signal due to tonic adenosine receptor activity is masked, ADP and ATP stimulated G-protein activity in multiple grey and white matter regions. Localization in the grey matter suggests inhibitory auto-/heteroreceptor function. In the white matter, activated G proteins appeared as ‘hot spots’ (presumed oligodendrocyte progenitors) with scattered distribution along the main fibre tracts. Responses to ATP were diminished under conditions that inhibited degradation, suggesting that prior conversion to ADP explained agonist action. Uracil nucleotides were ineffective but 2-methylthio-ADP activated G proteins ≈ 500-fold more potently than ADP, although both were similarly degraded. Throughout the brain, ADP-dependent G-protein activity was reversed by 2-hexylthio-AdoOC(O)Asp2, a non-phosphate ATP analogue, whereas selective P2Y1 receptor antagonists proved ineffective. A similar receptor was also disclosed from the adrenal medulla. These data witness a hitherto unrecognized abundance of Gi/o-linked ADP receptors in the nervous system. Biochemical and pharmacological behaviour suggests striking similarities to the elusive platelet P2YADP receptor.