Pharmacological parameters for agonist binding to A1R-A2AR and A2AR-D2R CHO cells.

Binding data from competition experiments were fitted assuming that receptors (also when heteromerizing) form homodimers, and cooperativity (DCB ≠ 0, fitting to eq. 2; Materials and Methods) or non-cooperativity (DCB = 0, fitting to eq. 3; Materials and Methods) in competitor ligand binding was statistically tested (F test). KDB1 and KDB2 are, respectively, the equilibrium dissociation constants of the first and second binding of B (the A1R, A2AR, or D2R agonists: R-PIA, CGS-21680 or quinpirole, respectively) to the dimer. DCB is the “dimer cooperativity” index for the binding of the ligand B, and B50 is the concentration providing half saturation for B. Data are mean ± S.E.M. values of three experiments.*: pDB1 values in A1R-A2AR and A2AR cells (Table 1); one-way ANOVA, followed by Newman-Keuls test.