2.3. Adenosine A1 receptor bioassay
The assay was performed as previously described (Chang et al.,
2004) except that the volume of the total mixture in the assay was
200 μL. The radioactive ligand used for the assay was 0.4 nM [3H]
DCPCX (8-cyclopentyl-1,3-dipropylxanthine) (Kd¼1.6 nM). Membranes
were prepared from Chinese hamster ovary (CHO) cells
stably expressing human adenosine receptors by a method previously
described (Dalpiaz et al., 1998). Non-specific binding was
determined by using 10 μM CPA (N6-cyclopentyladenosine).
The mixture consisting of 50 μL [3H] DPCPX, 50 μL CPA/50 mM
Tris–HCl buffer/test compounds in different concentrations,
50 μL 50 mM Tris–HCl buffer pH 7.4, and 50 μL of membrane
was incubated at 25 1C for 60 min and then filtered over a GF/B
Whatman filter under reduced pressure. The filters were washed
three times with 2 mL ice-cold 50 mM Tris/HCl buffer, pH 7.4, and
3.5 mL scintillation liquid was added to each filter. The radioactivity
of the washed filters was counted by a Hewlett-Packard
Tri–Carb 1500 liquid scintillation detector. Non-specific binding
was determined in the presence of 10–5 M CPA