Kollias-Baker C, Ruble J, Dennis D, Bruns R F, Linden J, Belardinelli L
Department of Medicine, University of Florida, Gainesville 32610.
Circ Res. 1994 Dec;75(6):961-71. doi: 10.1161/01.res.75.6.961.
The 2-amino-3-benzoylthiophene derivative PD 81,723 is an allosteric enhancer of agonist binding to brain A1 adenosine receptors. One aim of this study was to characterize and contrast the effects of PD 81,723 on the A1 receptor-mediated negative dromotropic and A2a receptor-mediated vasodilatory actions of adenosine and of a nonmetabolizable and unselective N6-(3-pentyl)adenosine derivative. A second aim was to determine the mechanism of action of PD 81,723. In guinea pig isolated hearts, PD 81,723 potentiated the adenosine and the N6-(3-pentyl)adenosine derivative-induced prolongations of the stimulus-to-His bundle (S-H) interval in a concentration-dependent manner. PD 81,723 (30 mumol/L) decreased the EC50 value for adenosine to prolong the S-H interval by ninefold from 7.4 +/- 1.2 to 0.8 +/- 0.1 mumol/L but did not increase the content of adenosine in cardiac effluent. PD 81,723 (30 mumol/L) increased the specific binding of the A1 agonist [3H]cyclohexyladenosine ([3H]CHA) to human atrial and guinea pig atrial and brain membranes by 38%, 78%, and 300%, respectively. PD 81,723 also increased the fraction of A1 receptors in the high-affinity binding state by an average of 56 +/- 13%. The dissociation rate of [3H]CHA from guinea pig brain membranes was decreased in the presence of PD 81,723 (10 mumol/L) from 0.55 +/- 0.01/min to 0.35 +/- 0.01/min. PD 81,723 did not alter the binding of the A1 antagonist [3H]cyclopentyldipropylxanthine to guinea pig brain membranes. The IC50 values for 5'-guanylylimidodiphosphate to reduce specific binding of [3H]CHA to guinea pig cardiac and brain membranes were increased from 1.5 +/- 0.2 and 2.0 +/- 0.2 mumol/L in the absence of PD 81,723 to 10 +/- 3.3 and 18 +/- 0.5 mumol/L, respectively, in the presence of PD 81,723 (30 mumol/L). PD 81,723 did not potentiate the coronary vasodilatory actions of the N6-(3-pentyl)adenosine derivative. Specific binding of the A2a agonist [3H]CGS 21680 to brain membranes and the nucleoside transporter ligand [3H]nitrobenzylthioinosine to cardiac membranes was unchanged in the presence of PD 81,723. The results suggest that PD 81,723 specifically potentiates the action of adenosine on A1 receptors by stabilizing receptor-G protein interactions in the presence of agonists.
2-氨基-3-苯甲酰基噻吩衍生物PD 81,723是激动剂与脑A1腺苷受体结合的变构增强剂。本研究的一个目的是表征和对比PD 81,723对腺苷以及一种不可代谢且无选择性的N6-(3-戊基)腺苷衍生物的A1受体介导的负性变传导作用和A2a受体介导的血管舒张作用的影响。第二个目的是确定PD 81,723的作用机制。在豚鼠离体心脏中，PD 81,723以浓度依赖性方式增强腺苷和N6-(3-戊基)腺苷衍生物诱导的刺激至希氏束（S-H）间期延长。PD 81,723（30 μmol/L）将腺苷延长S-H间期的EC50值从7.4±1.2 μmol/L降至0.8±0.1 μmol/L，降低了9倍，但并未增加心脏流出液中腺苷的含量。PD 81,723（30 μmol/L）使A1激动剂[3H]环己基腺苷（[3H]CHA）与人心房、豚鼠心房和脑膜的特异性结合分别增加了38%、78%和300%。PD 81,723还使处于高亲和力结合状态的A1受体比例平均增加了56±13%。在存在PD 81,723（10 μmol/L）的情况下，[3H]CHA从豚鼠脑膜的解离速率从0.55±0.01/min降至0.35±0.01/min。PD 81,723未改变A1拮抗剂[3H]环戊基二丙基黄嘌呤与豚鼠脑膜的结合。在不存在PD 81,723时，5'-鸟苷酰亚胺二磷酸降低[3H]CHA与豚鼠心脏和脑膜特异性结合的IC50值分别为1.5±0.2 μmol/L和2.0±0.2 μmol/L，在存在PD 81,723（30 μmol/L）时分别增至10±3.3 μmol/L和18±0.5 μmol/L。PD 81,723未增强N6-(3-戊基)腺苷衍生物的冠状血管舒张作用。在存在PD 81,723的情况下，A2a激动剂[3H]CGS 21680与脑膜的特异性结合以及核苷转运体配体[3H]硝基苄基硫代肌苷与心脏膜的特异性结合未发生变化。结果表明，PD 81,723通过在激动剂存在时稳定受体-G蛋白相互作用，特异性地增强腺苷对A1受体的作用。
