Chemicon's A1 membrane preparations are crude membrane preparations made from our proprietary stable recombinant cell lines to ensure high-level of GPCR surface expression; thus, they are ideal HTS tools for screening of antagonists of A1 interactions with its ligands. The membrane preparations exhibit a Kd of 1.2 nM for [3H]-Cyclopentyl-1, 3-dipropylxanthine, 8-[dipropyl-2, 3-3H (N)]. With 5mg/well A1 Membrane Prep and 20nM [3H]-DPCPX, a greater than 6-fold signal-to-background ratio is obtained.