MgCl2和Gpp(NH)p对腺苷A1受体激动剂和拮抗剂结合的作用比较

• 作者: Henry J OLVERMAN John SHARKEY Keith FINLAYSON MAEMOTO Takuya Steven P BUTCHER
• 来源期刊: 中国药理学报（英文版）
• 学科: 医学
• 关键词: 嘌呤P1受体 放射配位体测定 氯化镁 鸟苷酰亚氨二磷酸 脑
• 年，卷（期）: 2003,（8）
• 所属期刊栏目: 研究原著
• 页码范围: 729-740
• 页数: 12页
• 分类号: R96
• 语种: 英文

摘要

AIM: To investigate modulation of antagonist and agonist binding to adenosine A1 receptors by MgCl2 and 5'-guanylimidodiphosphate (Gpp(NH)p) using rat brain membranes and the A1 antagonist [3H]-8-cyclopentyl-1,3-dipropylxanthine ([3H]DPCPX) and the A1 agonist [3H]-2-chloro-N6-cyclopentyladenosine ([3H]CCPA). METHODS:Parallel saturation and inhibition studies were performed using well-characterised radioligand binding assays and aBrandel Cell Harvester. RESULTS: MgCl2 produced a concentration-dependent decrease (44 %), whereasGpp(NH)p increased [3H]DPCPX binding (19 %). In [3H]DPCPX competition studies, agonist affinity was 1.5-14.6-fold higher and 4.6-10-fold lower in the presence of 10 mmol/L MgCl2 and 10 μmol/L Gpp(NH)p respectively;antagonist affinity was unaffected. The decrease in agonist affinity with increasing Gpp(NH)p concentrations wasdue to a reduction in the proportion of binding to the high affinity receptor state. In contrast to [3H]DPCPX, MgCl2produced a concentration-dependent increase (72 %) and Gpp(NH)p a decrease (85 %) in [3H]CCPA binding.Using [3H]CCPA, agonist affinities were 5-17-fold higher than those for [3H]DPCPX, consistent with binding onlyto the high affinity receptor state. Agonist affinity was 1.3-10.5-fold higher and 2.4-4.7-fold lower on addingMgCl2 or Gpp(NH)p respectively; antagonist affinities were as for [3H]DPCPX. CONCLUSION: The inconsisten-cies surrounding the effects of MgCl2 and guanine nucleotides on radioligand binding to adenosine A1 receptorswere systematically examined. The effects of MgCl2 and Gpp(NH)p on agonist binding to A1 receptors are consis-tent with their roles in stimulating GTP-hydrolysis at the G-protein α-subunit and in blocking formation of the highaffinity agonist-receptor-G protein complex.