[3H]SCH 58261, a selective adenosine A2A receptor antagonist, is a useful ligand in autoradiographic studies.
We have characterized the new potent and selective nonxanthine adenosine A2A receptor antagonist SCH 58261 as a new radioligand for receptor autoradiography. In autoradiographic studies using agonist radioligands for A2A receptors ([3H]CGS 21680) or A1 receptors (N6-[3H]cyclohexyladenosine), it was found that SCH 58261 is close to 800-fold selective for rat brain A2A versus A1 receptors (Ki values of 1.2 nM versus 0.8 microM). Moreover, receptor autoradiography showed that [3H]SCH 58261, in concentrations below 2 nM, binds only to the dopamine-rich regions of the rat brain, with a K(D) value of 1.4 (0.8-1.8) nM. The maximal number of binding sites was 310 fmol/mg of protein in the striatum. Below concentrations of 3 nM, the nonspecific binding was <15%. Three adenosine analogues displaced all specific binding of [3H] SCH 58261 with the following estimated Ki values (nM): 2-hex-1-ynyl-5'-N-ethylcarboxamidoadenosine, 3.9 (1.8-8.4); CGS 21680, 130 (42-405); N6-cyclohexyladenosine, 9,985 (3,169-31,462). The binding of low concentrations of SCH 58261 was not influenced by either GTP (100 microM) or Mg2+ (10 mM). The present results show that in its tritium-labeled form, SCH 58261 appears to be a good radioligand for autoradiographic studies, because it does not suffer from some of the problems encountered with the currently used agonist radioligand [3H]CGS 21680.
Fredholm
B B
BB
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Lindström
K
K
Dionisotti
S
S
Ongini
E
E
D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D001345:Autoradiography / Q000379:methods*; D001667:Binding, Competitive; D019204:GTP-Binding Proteins / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000494:pharmacology; D008024:Ligands; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D010627:Phenethylamines / Q000494:pharmacology; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D011743:Pyrimidines / Q000494:pharmacology*; D011869:Radioligand Assay / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D043705:Receptor, Adenosine A2A; D014230:Triazoles / Q000494:pharmacology*; D014316:Tritium
C098657:5-amino-7-(2-phenylethyl)-2-(2-furyl)pyrazolo(4,3-e)-1,2,4-triazolo(1,5-c)pyrimidine; D000959:Antihypertensive Agents; D008024:Ligands; D010627:Phenethylamines; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D011743:Pyrimidines; D043705:Receptor, Adenosine A2A; D014230:Triazoles; D014316:Tritium; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins; D008274:Magnesium; D000241:Adenosine