2-[2-[4-[2-[2-[ 1,3-Dihydro- 1,1-bis (4-hydroxyphenyl)-3-oxo-5-isobenzofuranthioureidyl]ethylaminocarbonyl]ethyl]phenyl] ethylamino]-5'--ethylcarboxamidoadenosine (FITC-APEC): A Fluorescent Ligand For A-Adenosine Receptors.

The fluorescein conjugate, FITC-APEC (2-[2-[4-[2-[2-[1,3-dihydro-l,l-bis(4-hydroxyphenyl)-3-oxo-5-isobenzofuranthioureidyl]ethylaminocarbonyl]ethyl]phenyl]ethylamino]-5'--ethylcarboxamidoadenosine), is a novel ligand derived from a series of functionalized congeners that act as selective A-adenosine receptor agonists. The binding of FITC-APEC to bovine striatal A,-adenosine receptors measured by fluorescence techniques was saturable and of a high affinity, with a , of 2.3 ± 0.3 pmol/mg protein and of 57 ± 2 n. The value estimated by fluorescence was consistent with the (11 ± 0.3 n) obtained by competition studies with [H]CGS 21680. Additionally, the , value found by FITC-APEC measurement was in agreement with , values obtained using radioligand binding. FITC-APEC exhibited rapid and reversible binding to bovine striatum. The potencies of chemically diverse A-adenosine receptor ligands estimated by inhibition of FITC-APEC binding were in good agreement with their potencies determined using radioligand binding techniques ( = 0.97, = 0.0003). FITC-APEC binding was not altered by purine derivatives that do not recognize A-adenosine receptors. These findings demonstrate that the novel fluorescent ligand FITC-APEC can be used in the quantitative characterization of ligand binding to A-adenosine receptors.