百日咳毒素敏感的褪黑素受体与培养的人及大鼠视网膜色素上皮细胞相关联，且与腺苷酸环化酶呈负偶联。
Pertussis toxin-sensitive melatonin receptors negatively coupled to adenylate cyclase associated with cultured human and rat retinal pigment epithelial cells.
作者信息
Nash M S, Osborne N N
机构信息
Nuffield Laboratory of Ophthalmology, University of Oxford, United Kingdom.
出版信息
Invest Ophthalmol Vis Sci. 1995 Jan;36(1):95-102.
PURPOSE
Studies were conducted to investigate the influence of melatonin on adenylate cyclase activity in cultured human and rat retinal pigment epithelial (RPE) cells.
METHODS
Adenylate cyclase activity was assessed by measurement of cAMP levels in cultured RPE cells using a specific cAMP-binding protein isolated from bovine adrenal cortex to detect cellular cAMP by competition with a standard amount of tritiated cAMP. The effects of melatonin on basal cAMP levels and those induced by the direct activator of adenylate cyclase, forskolin, were studied.
RESULTS
Exposure of human RPE cells to 100 microM of melatonin had no effect on basal cAMP levels, but it caused a 41% reduction in the forskolin (5 microM) stimulation of cAMP. This melatonin-induced reduction in forskolin-stimulated adenylate cyclase activity was dose dependent, with half-maximal (EC50) reduction at 4.2 x 10(-10) M. 2-iodomelatonin, 6-chloromelatonin, and 6-hydroxymelatonin mimicked the melatonin effect with EC50 values of 3.5 x 10(-10) M, 4.3 x 10(-9)M, and 1.9 x 10(-7)M, respectively. Preexposure of cells to pertussis toxin (100 ng/ml) for 18 hours completely attenuated the ability of melatonin to influence the forskolin stimulation of cAMP levels. Propranolol did not influence the action of melatonin but did antagonize the ability of serotonin to reduce the forskolin-elevated cAMP levels. Thus, melatonin receptors are distinct from serotonin receptors. Melatonin receptors negatively linked to cAMP metabolism are also associated with cultured hooded rat RPE cells. Melatonin and iodomelatonin caused dose-dependent reductions in forskolin-stimulated cAMP production with half-maximal values of 2.4 x 10(-9)M and 3.28 x 10(-9)M, respectively.
CONCLUSIONS
The results show that human and rat RPE cells possess melatonin receptors negatively coupled to adenylate cyclase and sensitive to pertussis toxin.
目的
开展研究以调查褪黑素对培养的人及大鼠视网膜色素上皮（RPE）细胞中腺苷酸环化酶活性的影响。
方法
通过使用从牛肾上腺皮质分离的特异性环磷酸腺苷（cAMP）结合蛋白来测量培养的RPE细胞中的cAMP水平，以检测细胞内的cAMP，该蛋白通过与标准量的氚化cAMP竞争来实现检测。研究了褪黑素对基础cAMP水平以及由腺苷酸环化酶直接激活剂福司可林诱导的cAMP水平的影响。
结果
将人RPE细胞暴露于100微摩尔的褪黑素对基础cAMP水平无影响，但导致福司可林（5微摩尔）刺激的cAMP降低了41%。这种褪黑素诱导的福司可林刺激的腺苷酸环化酶活性降低呈剂量依赖性，在4.2×10⁻¹⁰摩尔时出现半数最大（EC50）降低。2 - 碘褪黑素、6 - 氯褪黑素和6 - 羟基褪黑素模拟了褪黑素的作用，其EC50值分别为3.5×10⁻¹⁰摩尔、4.3×10⁻⁹摩尔和1.9×10⁻⁷摩尔。将细胞预先暴露于百日咳毒素（100纳克/毫升）18小时可完全减弱褪黑素影响福司可林刺激的cAMP水平的能力。普萘洛尔不影响褪黑素的作用，但可拮抗血清素降低福司可林升高的cAMP水平的能力。因此，褪黑素受体与血清素受体不同。与cAMP代谢负相关的褪黑素受体也与培养的有帽大鼠RPE细胞相关。褪黑素和碘褪黑素导致福司可林刺激的cAMP产生呈剂量依赖性降低，半数最大值分别为2.4×10⁻⁹摩尔和3.28×10⁻⁹摩尔。
结论
结果表明，人和大鼠RPE细胞具有与腺苷酸环化酶负偶联且对百日咳毒素敏感的褪黑素受体。
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