Abbracchio M P, Brambilla R, Ceruti S, Kim H O, von Lubitz D K, Jacobson K A, Cattabeni F
Institute of Pharmacological Sciences, University of Milan, School of Pharmacy, Italy.
Mol Pharmacol. 1995 Dec;48(6):1038-45.
The recently cloned G protein-coupled adenosine A3 receptor has been proposed to play a role in the pathophysiology of cerebral ischemia. Because phospholipase C activation occurs as a very early response to brain ischemia, we evaluated the ability of A3- selective and nonselective adenosine analogues to elicit phosphoinositide hydrolysis. In myo-[3H]inositol-labeled rat striatal and hippocampal slices, A3 agonists stimulated formation of [3H]inositol phosphates in a concentration-dependent manner. In striatum, the potency order was 2-chloro-N6-(3-iodobenzyl)- adenosine-5'-N-methyluronamide > or = N6-(3-iodobenzyl)- adenosine-5'-N-methyluronamide >> N-methyl-1,3-di-n-butylxanthine-7-beta-D-ribofuronamide > or = 5'-N-ethylcarboxamidoadenosine > or = N6-2-(4-aminophenyl)-ethyladenosine > N6-(p-sulfophenyl)-adenosine = 1,3-dibutylxanthine-7- riboside, which is identical to the potency order in binding studies at cloned rat A3 receptors. Stimulation of phospholipase C activity was abolished by guanosine-5'-O-(2-thiodiphosphate), confirming the involvement of a G protein-coupled receptor. Activation of phospholipase C was higher in the striatum than in the hippocampus, consistent with A3 receptor densities. Stimulation of phospholipase C activity by adenosine analogues was only modestly antagonized by xanthine derivatives and at much higher concentrations than needed for blocking adenosine A1, A2A, and A2b receptors. In the presence of an A1/A2 antagonist, a selective A3 in rat striation. Thus, stimulation of phospholipase C activity agonist only weakly inhibited forskolin-stimulated adenylyl cyclase activity represents a principal transduction mechanism for A3 receptors in mammalian brain, and perhaps A3 receptor-mediated increases of inositol phosphates in the ischemic brain contribute to neurodegeneration by raising intracellular calcium levels.
最近克隆出的G蛋白偶联腺苷A3受体被认为在脑缺血的病理生理学中发挥作用。由于磷脂酶C的激活是对脑缺血的一种非常早期的反应，我们评估了A3选择性和非选择性腺苷类似物引发磷酸肌醇水解的能力。在肌醇-[3H]标记的大鼠纹状体和海马切片中，A3激动剂以浓度依赖的方式刺激[3H]肌醇磷酸的形成。在纹状体中，效力顺序为2-氯-N6-(3-碘苄基)-腺苷-5'-N-甲基脲苷≥N6-(3-碘苄基)-腺苷-5'-N-甲基脲苷>>N-甲基-1,3-二正丁基黄嘌呤-7-β-D-核糖呋喃酰胺≥5'-N-乙基羧酰胺腺苷≥N6-2-(4-氨基苯基)-乙基腺苷>N6-(对磺基苯基)-腺苷=1,3-二丁基黄嘌呤-7-核糖苷，这与在克隆的大鼠A3受体上进行结合研究时的效力顺序相同。鸟苷-5'-O-(2-硫代二磷酸)消除了对磷脂酶C活性的刺激，证实了G蛋白偶联受体的参与。纹状体中磷脂酶C的激活高于海马体，这与A3受体密度一致。腺苷类似物对磷脂酶C活性的刺激仅被黄嘌呤衍生物适度拮抗，且所需浓度远高于阻断腺苷A1、A2A和A2b受体所需的浓度。在存在A1/A2拮抗剂的情况下，大鼠纹状体中的选择性A3。因此，对磷脂酶C活性的刺激激动剂仅微弱抑制福司可林刺激的腺苷酸环化酶活性代表了哺乳动物脑中A3受体的主要转导机制，并且也许缺血脑中A3受体介导的肌醇磷酸增加通过提高细胞内钙水平而导致神经退行性变。
