Nash M S, Osborne N N
Nuffield Laboratory of Ophthalmology, University of Oxford, England.
Neurochem Int. 1995 Sep;27(3):253-62. doi: 10.1016/0197-0186(95)00040-f.
Recent work has demonstrated that stimulation of cAMP production via A2-adenosine receptors is reduced in cultured retinal pigment epithelial cells from the RCS rat. Cultured rat RPE cells are also shown to possess beta 2-adrenergic receptors positively coupled to cAMP production. Isoproterenol and salbutamol both stimulate cAMP levels with half maximal (EC50) values of 0.5 and 0.2 microM, respectively. Isoproterenol action is attenuated most effectively by the beta 2-antagonist, ICI 118551, while the beta 1-antagonist, CGP 20712A, is only partially effective. Isoproterenol-stimulated cAMP production is markedly reduced in the RCS rat RPE when compared to control cultures. In passaged RCS rat RPE cells cAMP stimulation by 10 microM isoproterenol was 6.4% of that by control cultures and in primary cultures it was around 75% of controls. The observed EC50 values were 0.4 and 1.3 microM for passaged control and RCS rat RPE cells, respectively. Melatonin negatively influences cAMP production in the RPE via Gi-proteins. Melatonin attenuated the action of forskolin by 51.1% in control rat RPE but only by 18.6% in the RCS rat RPE. The dose-response curve for melatonin shows an approximate 1000-fold shift in potency in the RCS rat. bFGF also has an inhibitory effect on rat RPE cells. bFGF (50ng/ml) attenuated forskolin-stimulated cAMP levels by 61.9% in control rat RPE but had not effect on the action of forskolin in RCS rat RPE. Serotonin (100 microM) potentiates the forskolin-induced stimulation of cAMP by 140.1%. However, unlike isoproterenol, melatonin and bFGF, the action of serotonin on adenylate cyclase appears normal in the RCS rat RPE. We conclude that the defect in the RCS rat RPE is likely to be due to impaired coupling of the components of the adenylate cyclase system and that this is most probably an abnormal interaction of adenylate cyclase with G-protein alpha-subunits.
最近的研究表明，在RCS大鼠的培养视网膜色素上皮细胞中，通过A2-腺苷受体刺激cAMP生成的能力降低。培养的大鼠RPE细胞也显示出具有与cAMP生成呈正相关的β2-肾上腺素能受体。异丙肾上腺素和沙丁胺醇均可刺激cAMP水平，其半数最大效应浓度（EC50）值分别为0.5和0.2微摩尔。β2-拮抗剂ICI 118551能最有效地减弱异丙肾上腺素的作用，而β1-拮抗剂CGP 20712A仅部分有效。与对照培养物相比，RCS大鼠RPE中异丙肾上腺素刺激的cAMP生成明显减少。在传代的RCS大鼠RPE细胞中，10微摩尔异丙肾上腺素刺激产生的cAMP是对照培养物的6.4%，在原代培养物中约为对照的75%。传代对照和RCS大鼠RPE细胞的观察到的EC50值分别为0.4和1.3微摩尔。褪黑素通过Gi蛋白对RPE中的cAMP生成产生负面影响。褪黑素在对照大鼠RPE中使福斯可林的作用减弱51.1%，但在RCS大鼠RPE中仅减弱18.6%。褪黑素的剂量反应曲线显示在RCS大鼠中效力有大约1000倍的变化。碱性成纤维细胞生长因子（bFGF）对大鼠RPE细胞也有抑制作用。bFGF（50纳克/毫升）在对照大鼠RPE中使福斯可林刺激的cAMP水平降低61.9%，但对RCS大鼠RPE中福斯可林的作用没有影响。血清素（100微摩尔）使福斯可林诱导的cAMP刺激增强140.1%。然而，与异丙肾上腺素、褪黑素和bFGF不同，血清素对腺苷酸环化酶的作用在RCS大鼠RPE中似乎正常。我们得出结论，RCS大鼠RPE中的缺陷可能是由于腺苷酸环化酶系统各组分的偶联受损，这很可能是腺苷酸环化酶与G蛋白α亚基之间的异常相互作用。
