Capsoni S, Viswanathan M, De Oliveira A M, Saavedra J M
Section on Pharmacology, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland 20892.
Endocrinology. 1994 Jul;135(1):373-8. doi: 10.1210/endo.135.1.8013371.
The aims of this study were to characterize the melatonin receptors in rat brain arteries forming the circle of Willis. Saturation studies performed using in vitro autoradiography and [125I]iodomelatonin revealed the presence of two binding sites: one with a Kd of 13 pM, and the second characterized by a Kd of 832 pM. Coincubation with a nonhydrolyzable guanine nucleotide analog [guanosine-5'-O-(3-thiotriphosphate)] inhibited 2-[125I]iodomelatonin binding in a concentration-dependent manner, whereas adenine nucleotide adenosine-5'-O-(3-thiotriphosphate) was ineffective. In saturation studies performed in the presence of guanosine-5'-O-(3-thiotriphosphate), the high affinity site was no longer detectable, and the affinity of the receptor was decreased to the high picomolar range. Melatonin, at nanomolar concentrations, was able to inhibit forskolin-stimulated cAMP production in rat circle of Willis arteries. Preincubation with pertussis toxin counteracted the effect of melatonin. Our results demonstrate that melatonin receptors in rat cerebral arteries are linked to their second messenger through a pertussis toxin-sensitive G-protein, similar to what has been described for melatonin receptors in different areas of vertebrate brain.
本研究的目的是对构成 Willis 环的大鼠脑动脉中的褪黑素受体进行表征。使用体外放射自显影和 [125I] 碘褪黑素进行的饱和研究揭示了两个结合位点的存在：一个的解离常数（Kd）为 13 pM，另一个的 Kd 为 832 pM。与不可水解的鸟嘌呤核苷酸类似物 [鸟苷 - 5'-O-(3-硫代三磷酸)] 共同孵育以浓度依赖的方式抑制了 2-[125I] 碘褪黑素的结合，而腺嘌呤核苷酸腺苷 - 5'-O-(3-硫代三磷酸) 则无效。在存在鸟苷 - 5'-O-(3-硫代三磷酸) 的情况下进行的饱和研究中，高亲和力位点不再可检测到，并且受体的亲和力降低到高皮摩尔范围。纳摩尔浓度的褪黑素能够抑制大鼠 Willis 环动脉中福斯高林刺激的环磷酸腺苷（cAMP）产生。用百日咳毒素预孵育可抵消褪黑素的作用。我们的结果表明，大鼠脑动脉中的褪黑素受体通过对百日咳毒素敏感的 G 蛋白与其第二信使相连，这与脊椎动物脑不同区域中褪黑素受体的情况类似。
