An antagonist of P2X receptors and a fluorescent probe; an antagonist at the purinergic receptor subtypes P2X1, P2X3, and P2X2/3 (IC50s = 6, 0.9, and 7 nM, respectively); selective over P2X2, P2X4, and P2X7 receptors (IC50s = 2,000, 15,200, and >30,000 nM, respectively); inhibits calcium flux in 1321N1 cells expressing P2X3 and P2X2/3 receptors (IC50s = 10 and 62 nM, respectively); reduces acetic-acid induced writhing in a mouse model of visceral pain (ED50 = 6.35 μmol/kg); fluorescent probe for ATP-binding enzyme activity with ex/em = 403 and 547 nm, respectively, with a four-fold increase in intensity and an emission shift to 538 nm upon binding to the ATP-binding enzyme IDE ,