(A) Displacement of specific [3H]-DPCPX binding from the adenosine A1 receptor at 25°C by CCPA in the absence or presence of 10 μM PD81,723, 10 μM BC-1, 1 mM GTP or a combination thereof. (B) Displacement of specific [3H]-DPCPX binding from the adenosine A1 receptor at 25°C by NECA in the absence or presence of 10 μM PD81,723, 10 μM BC-1, 1 mM GTP or a combination thereof. (C) Displacement of specific [3H]-DPCPX binding from the adenosine A1 receptor at 25°C by LUF5834 in the absence or presence of 10 μM PD81,723 or BC-1. (D) Displacement of specific [3H]-DPCPX binding from the adenosine A1 receptor at 25°C by 100 nM CCPA (normalized as 100%) in the presence of increased concentrations of PD81,723 or BC-1. Representative graphs from one experiment performed in duplicate.