Table 1.

Inhibition of [³H]XAC^a binding by adenosine receptor agonists and antagonists in bovine cortical and cardiac membranes. K_H and K_L are the dissociation constants for the high and low affinity states determined by LIGAND. %H is the percentage of high affinity binding sites. Values are means ± SEM for 3 experiments

Compound	Cortex			Heart
	KH, nM	KL, nM	%H	KH, nM	KL, nM	%H
R-PIA	0.07 ± 0.02	4.5 ± 2.1	81 ± 7	0.36 ± 0.16	4000 ± 1600	57 ± 7
S-PIA	1.30 ± 0.40	140.0 ± 40.0	83 ± 7	5.30 ± 2.20	5500 ± 2200	61 ± 6
CHA	0.14± 0.04	8.3 ± 3.1	76 ± 6	0.67 ± 0.44	5200 ±3200	66 ±11
IABA	0.21 ± 0.11	18.0 ± 12.9	78 ±10	0.40 ± 0.21	4700 ±2700	65 ± 9
NECA	13.0 ± 5.2	700 ± 400	74 ± 10	14.7 ± 16.0	900 ± 600	41 ± 14
NCCA	5.3 ± 5.5	1376 ± 886	51 ± 13	3.8 ± 7.6	1000 ± 800	41 ± 25
Theophylline	9600 ± 1400	–	–	32500 ± 7900	–	–
XAC	0.17 ± 0.01	–	–	0.20 ± 0.07	–	–

^a[³H]XAC was present in concentrations of 0.06 – 0.07 nM for cortical membranes and 0.15–0.25 nM for cardiac membranes