Adenosine Binding Sites of Rat Pheochromocytoma PC 12 Cell Membranes: Partial Characterization and Solubilization1

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Abstract
Rat pheochromocytoma PC 12 cell membranes were shown to possess A2-like adenosine binding sites as assessed by using 5′-N-ethylcarboxamide[3H]adenosine ([3H]NECA). Specific [3H]NECA binding to PC 12 cell membrane at 0°C was saturable and showed a monophasic saturation profile. In contrast,[3H]NECA binding to PC 12 cell membrane at 30°C exhibited a biphasic profile suggesting the presence of two specific binding site. The rank order of potency for inhibition of [3H] binding at 0°C was NECA>2-chloroadenosine> 2′,5′-dideoxyadenosine> isobutylmethylxanthine » phenylisopropyladenosine. These adenosine binding sites were solubilized with sodium cholate and the solubilized portion retained the same ligand binding characteristics as those of the membranebound form. Gel filtration experiments indicated an apparent Stokes radius of 6.7 nm for these adenosine binding sites/detergent complexes.