In vitro activity: AK enzyme inhibition was assayed radiochemically as described byYamada et al. (1980) and McNally et al. (1997). The ability of A-134974 to inhibit AK activity in intact IMR-32 neuroblastoma cells (American Type Culture Collection, Gaithersburg, MD) carried out as previously described (Kowaluk and Cowart, 1994). Radioligand binding assay methodology for the A1, A2A, and A3 receptors was carried out as described by Jarvis et al. (2000). The ability of A-134974 to inhibit [3H]nitrobenzylthioinosine binding to the ADO transporter and to inhibit adenosine deaminase activity was also examined using previously described methodology (Parkinson and Geiger, 1996).