Table 1.

Comparison of the ligand-binding properties of A₁R and its heteromers

	Radioligand
	[3H]DPCPX		[3H]NECA		[3H]R-PIA
	KD, nM	Bmax, pmol/mg	KD, nM	Bmax, pmol/mg	KD, nM	Bmax, pmol/mg
A1R	1.3  ± 0.14	3.5  ± 0.12	—	—	—	—
HA-A1R	1.2  ± 0.12	3.6  ± 0.11	3.4  ± 1.2	0.11  ± 0.07	0.85  ± 0.3	0.09  ± 0.02
HA-A1R + Myc-P2Y1R	1.2  ± 0.1	1.9  ± 0.05*	3.5  ± 1.8	0.09  ± 0.03	3.1  ± 1.7*	0.08  ± 0.03

For an A₁R antagonist [³H]DPCPX saturation experiment, 10 μg of membrane protein was incubated with 0.2–10 nM [³H]DPCPX containing 2 units/ml adenosine deaminase, 5 mM MgCl₂, and 50 mM Tris-acetate buffer, pH 7.4 for 60 min at 25°C. Nonspecific binding was measured in the presence of 1 μM XAC. For agonist [³H]NECA and [³H]R-PIA saturation experiment, 30–50 μg of membrane proteins was incubated with 2–50 nM radioligands in the same condition described above. The binding of these ligands to Myc-P2Y₁R was not detected.  

^*, P < 0.05 (Student's t test, n = 3).