Table 1.

Approximated IC₅₀ values (μM) of agonists and antagonists obtained in radioligand binding studies with [³H]XAC on the wild-type (WT) and E13Q mutant of the cloned human adenosine A_2A receptor (n = 2, with individual IC₅₀ values differing less than 30%: CGS21680 alone: n = 3, IC₅₀ ± S.E.M.)

Compounds	WT	E13Q	Shifta
Agonist
CGS21680	0.85 ± 0.22	13.0 ± 4.3	15
CGS21680 +GTPb	1.65	24.8	15
CGS21680 +GTPb+NaClc	10.5	37.9	3.6
Antagonists
XAC	0.018	0.042	2.3
CGS 15943	0.0022	0.0027	1.2
Amiloride	52	46	0.9

^aIC_{50. E13Q}/IC_{50. WT}.

^bGTP concentration (final): 1 mM.

^cNaCl concentration (final): 1 M.