Jarvis M F, Gessner G, Shapiro G, Merkel L, Myers M, Cox B F, Martin G E
Rhone-Poulenc Rorer Central Research, Collegeville, PA, USA.
Brain Res. 1999 Sep 4;840(1-2):75-83. doi: 10.1016/s0006-8993(99)01747-3.
The benzoylthiophene analog, PD 81,723, has been shown to allosterically enhance agonist binding and functional activation of the mammalian adenosine (ADO) A(1) receptor subtype by putatively maintaining the receptor in a high affinity state. The present studies were conducted to evaluate the ability of PD 81,723 to enhance the binding of [3H]cyclohexyladenosine ([3H]CHA) to A(1) receptors of neural (cerebral cortex) and non-neural (adipocyte) origin in three different species; rat, guinea pig and dog. PD 81, 723 (0.3-100 microM) produced a concentration-dependent enhancement of [3H]CHA binding to rat brain A(1) receptors. These effects were also species-dependent with larger enhancements (150-200% of control) observed in guinea pig and dog brain membranes as compared to the rat (120% of control). In contrast, PD 81,723 did not produce any enhancement of [3H]CHA binding to A(1) receptors in adipocyte membranes from any of the species examined. Additional binding studies were conducted using pharmacological manipulations that have previously been shown to enhance the allosteric effects of PD 81,723. In the presence of 1 mM GTP, the allosteric effects of PD 81,723 (15 microM) were increased in rat, guinea pig and dog brain membranes, however, in adipocyte membranes from each species, no significant alteration in agonist binding was observed. Similarly, the A(1) receptor selective antagonist 8-cyclopentyl-1, 3-dipropylxanthine (added to effectively reduce the intrinsic antagonist properties of PD 81,723) was found to enhance the allosteric effects of PD 81,723 (15 microM) in brain, but produce no alteration of agonist binding in adipocyte membranes from each species. Examination of the dissociation kinetics of [3H]CHA binding from rat brain and adipocyte membranes revealed that PD 81,723 (15 microM) differentially slowed agonist dissociation from brain, but not adipocyte, membranes. Taken together, the present data support the hypothesis that in tissues that are sensitive to PD 81,723, this benzyolthiophene functions to maintain the A(1) receptor in a high-affinity state and that the relative proportions of high-affinity A(1) receptors present in specific tissues may contribute, at least in part, to the apparent differential effects of PD 81,723 on agonist binding. The tissue specific modulation of A(1) receptor function by PD 81,723 also illustrates the possibility that the locus of allosteric modulation by PD 81,723 may be manifest via a specific, but indirect and tissue-dependent, interaction with the A(1) receptor.
苯甲酰噻吩类似物PD 81,723已被证明可通过假定将受体维持在高亲和力状态来变构增强哺乳动物腺苷（ADO）A(1)受体亚型的激动剂结合和功能激活。进行本研究以评估PD 81,723增强[3H]环己基腺苷（[3H]CHA）与三种不同物种（大鼠、豚鼠和狗）的神经（大脑皮层）和非神经（脂肪细胞）来源的A(1)受体结合的能力。PD 81,723（0.3 - 100 microM）使[3H]CHA与大鼠脑A(1)受体的结合呈浓度依赖性增强。这些效应也具有物种依赖性，与大鼠（对照的120%）相比，在豚鼠和狗脑膜中观察到更大的增强（对照的150 - 200%）。相反，PD 81,723对所检测的任何物种的脂肪细胞膜中[3H]CHA与A(1)受体的结合均未产生任何增强作用。使用先前已证明可增强PD 81,723变构效应的药理学操作进行了额外的结合研究。在1 mM GTP存在下，PD 81,723（15 microM）在大鼠、豚鼠和狗脑膜中的变构效应增强，然而，在每个物种的脂肪细胞膜中，未观察到激动剂结合的显著改变。同样，发现A(1)受体选择性拮抗剂8 - 环戊基 - 1,3 - 二丙基黄嘌呤（添加以有效降低PD 81,723的内在拮抗剂特性）可增强PD 81,723（15 microM）在脑中的变构效应，但对每个物种的脂肪细胞膜中的激动剂结合无改变。对大鼠脑和脂肪细胞膜中[3H]CHA结合的解离动力学研究表明，PD （15 microM）差异性地减缓了激动剂从脑细胞膜而非脂肪细胞膜的解离。综上所述，目前的数据支持以下假设：在对PD 81,723敏感的组织中，这种苯甲酰噻吩的作用是将A(1)受体维持在高亲和力状态，并且特定组织中存在的高亲和力A(1)受体的相对比例可能至少部分地导致了PD 81,723对激动剂结合的明显差异效应。PD 81,723对A(1)受体功能的组织特异性调节也说明了PD 81,723变构调节位点可能通过与A(1)受体的特定但间接且依赖于组织的相互作用而表现出来的可能性。
