Hermans E, Gailly P, Gillis J M, Octave J N, Maloteaux J M
Laboratory of Neurochemistry, Catholic University of Louvain, Brussels, Belgium.
J Neurochem. 1995 Jun;64(6):2518-25. doi: 10.1046/j.1471-4159.1995.64062518.x.
Transfected Chinese hamster ovary cells were used as a model for the study of the desensitization of the neurotensin receptor at the second messenger level. Stimulation with nanomolar concentrations of neurotensin elicited rapid rises in the cytosolic calcium concentration ([Ca2+]i), which remained elevated throughout the peptide application. A significant response was already detected with neurotensin concentrations as low as 0.01 nM. This high efficiency of neurotensin in mediating this calcium response contrasts with the nanomolar affinity of the peptide for its receptor measured in binding experiments. Evidence indicated that the initial elevation of the [Ca2+]i resulted from release of Ca2+ from intracellular stores, whereas the sustained response involved an influx of extracellular origin. Return to the basal level was only reached after extensive washing of the peptide or its displacement with the neurotensin receptor antagonist SR48692. After washing, further stimulations were still able to mediate an increase in the [Ca2+]i, indicating an apparent absence of rapid desensitization of the intracellular signaling pathway that mediates calcium mobilization. In contrast with this absence of response desensitization, the neurotensin receptors were found to internalize after stimulation with the peptide. This internalization was maximal after 30 min and accounted for approximately 70% of the number of neurotensin binding sites located at the cell surface. These results indicate that despite the functional properties of the rat neurotensin receptor present in Chinese hamster ovary cells after transfection, the intracellular signaling pathway triggered by stimulation with neurotensin seems to be resistant to desensitization. This might be related to the high efficiency of the intracellular signaling pathway coupled to the neurotensin receptor observed in these cells.(ABSTRACT TRUNCATED AT 250 WORDS)
转染的中国仓鼠卵巢细胞被用作在第二信使水平研究神经降压素受体脱敏的模型。用纳摩尔浓度的神经降压素刺激可引起胞质钙浓度（[Ca2+]i）迅速升高，在整个肽应用过程中该浓度一直保持升高。神经降压素浓度低至0.01 nM时就已检测到显著反应。神经降压素介导这种钙反应的高效性与在结合实验中测得的该肽对其受体的纳摩尔亲和力形成对比。有证据表明，[Ca2+]i的初始升高源于细胞内钙库中Ca2+的释放，而持续反应涉及细胞外来源的钙内流。只有在大量冲洗该肽或用神经降压素受体拮抗剂SR48692取代后才会恢复到基础水平。冲洗后，进一步刺激仍能介导[Ca2+]i升高，表明介导钙动员的细胞内信号通路明显不存在快速脱敏现象。与这种反应脱敏的缺失相反，发现用该肽刺激后神经降压素受体会内化。这种内化在30分钟后达到最大值，约占位于细胞表面的神经降压素结合位点数量的70%。这些结果表明，尽管转染后中国仓鼠卵巢细胞中存在大鼠神经降压素受体的功能特性，但神经降压素刺激引发的细胞内信号通路似乎对脱敏具有抗性。这可能与在这些细胞中观察到的与神经降压素受体偶联的细胞内信号通路的高效性有关。（摘要截断于250字）
