Figure 1.

Effects of various treatments on the binding of [³H]DPCPX (1 nM) to human A₁ receptors stably expressed in CHO cell membranes. (a) Membranes had no pretreatment during preparation prior to addition of the indicated treatment. [³H]DPCPX-specific binding in the absence of any treatment was 188±22 fmol mg⁻¹ protein, in the presence of 0.1 U ml⁻¹ ADA was 396±28 fmol mg⁻¹ protein, in the presence of 100 μM Gpp(NH)p was 380±26 fmol mg⁻¹ protein and in the presence of both 0.1 U ml⁻¹ ADA and 100 μM Gpp(NH)p was 423±30 fmol ml⁻¹ protein. ^**P<0.01; ^***P<0.001; one-way ANOVA with Bonferroni post-test. (b) Membranes were pretreated with 10 U ml⁻¹ ADA during preparation (as indicated in the Methods) prior to addition of the indicated treatment. [³H]DPCPX-specific binding in the absence of any treatment was 269±16 fmol mg⁻¹ protein, in the presence of 0.1 U ml⁻¹ ADA was 291±12 fmol mg⁻¹ protein, in the presence of 100 μM Gpp(NH)p was 309±15 fmol mg⁻¹ protein and in the presence of both 0.1 U ml⁻¹ ADA and 100 μM Gpp(NH)p was 311±20 fmol mg⁻¹ protein. In all cases, incubation was for 90 min at 25°C in 50 mM Tris(HCl) buffer. Nonspecific binding was defined using 10 μM R-PIA. Data points represent the mean±s.e.m. obtained from five separate experiments performed in triplicate. There were no significant differences (P>0.05) between groups.