Leid M, Schimerlik M I, Murray T F
College of Pharmacy, Oregon State University, Corvallis 97331.
Mol Pharmacol. 1988 Sep;34(3):334-9.
The agonist radioligand (-)-N6-[125I]-p-hydroxyphenylisopropyl-adenosine ([ 125I]HPIA) was used to characterize adenosine recognition sites in porcine atrial membranes. [125I]HPIA showed saturable binding to an apparently homogeneous population of sites with a maximum binding capacity of 35 +/- 3 fmol/mg of protein and an equilibrium dissociation constant of 2.5 +/- 0.4 nM. Kinetic experiments were performed to address the molecular mechanism of [125I]HPIA binding in porcine atrial membranes. [125I]HPIA apparently interacts with the cardiac adenosine receptor in a simple bimolecular reaction. A kinetically derived [125I] HPIA dissociation constant (2.4 nM) was in good agreement with that parameter measured at equilibrium. Guanyl nucleotides negatively modulated [125I]HPIA binding by increasing its rate of dissociation. This finding is consonant with the formation of a ternary complex in porcine atrial membranes, consisting of ligand, receptor, and guanyl nucleotide-binding protein. Prototypic adenosine receptor agonists and antagonists inhibited specific binding in a manner consistent with the labeling of an A1 adenosine receptor. The results of these experiments suggest that the adenosine receptor present in porcine atrial membranes, as labeled by [125I]HPIA, is of the A1 subtype.
激动剂放射性配体（-）-N6-[125I]-对羟基苯异丙基腺苷（[125I]HPIA）用于表征猪心房膜中的腺苷识别位点。[125I]HPIA对一组明显同质的位点表现出饱和结合，最大结合容量为35±3 fmol/mg蛋白质，平衡解离常数为2.5±0.4 nM。进行动力学实验以探讨[125I]HPIA在猪心房膜中结合的分子机制。[125I]HPIA显然以简单的双分子反应与心脏腺苷受体相互作用。动力学推导的[125I]HPIA解离常数（2.4 nM）与在平衡时测量的该参数非常一致。鸟苷酸通过增加其解离速率对[125I]HPIA结合产生负调节作用。这一发现与猪心房膜中由配体、受体和鸟苷酸结合蛋白组成的三元复合物的形成相一致。典型的腺苷受体激动剂和拮抗剂以与A1腺苷受体标记一致的方式抑制特异性结合。这些实验结果表明，由[125I]HPIA标记的猪心房膜中存在的腺苷受体是A1亚型。
