Gauna Carlotta, van de Zande Bedette, van Kerkwijk Anke, Themmen Axel P N, van der Lely A J, Delhanty Patric J D
Department of Internal Medicine, Erasmus MC, Rotterdam, The Netherlands.
Mol Cell Endocrinol. 2007 Aug 15;274(1-2):30-4. doi: 10.1016/j.mce.2007.05.010. Epub 2007 May 21.
Recent findings demonstrate that the effects of ghrelin can be abrogated by co-administered unacylated ghrelin (UAG). Since the general consensus is that UAG does not interact with the type 1a growth hormone secretagogue receptor (GHS-R), a possible mechanism of action for this antagonistic effect is via another receptor. However, functional antagonism of the GHS-R by UAG has not been explored extensively. In this study we used human GHS-R and aequorin expressing CHO-K1 cells to measure Ca(2+) following treatment with UAG. UAG at up to 10(-5)M did not antagonize ghrelin induced Ca(2+). However, UAG was found to be a full agonist of the GHS-R with an EC(50) of between 1.6 and 2 microM using this in vitro system. Correspondingly, UAG displaced radio-labeled ghrelin from the GHS-R with an IC(50) of 13 microM. In addition, GHS-R antagonists were found to block UAG induced Ca(2+) with approximately similar potency to their effect on ghrelin activation of the GHS-R, suggesting a similar mode of action. These findings demonstrate in a defined system that UAG does not antagonize activation of the GHS-R by ghrelin. But our findings also emphasize the importance of assessing the concentration of UAG used in both in vitro and in vivo experimental systems that are aimed at examining GHS-R independent effects. Where local concentrations of UAG may reach the high nanomolar to micromolar range, assignment of GHS-R independent effects should be made with caution.
最近的研究结果表明，共同施用去酰基胃饥饿素（UAG）可消除胃饥饿素的作用。由于普遍的共识是UAG不与1a型生长激素促分泌素受体（GHS-R）相互作用，这种拮抗作用的一种可能作用机制是通过另一种受体。然而，UAG对GHS-R的功能拮抗作用尚未得到广泛研究。在本研究中，我们使用人GHS-R和表达水母发光蛋白的CHO-K1细胞来测量用UAG处理后的细胞内钙离子浓度（Ca(2+)）。高达10(-5)M的UAG并未拮抗胃饥饿素诱导的Ca(2+)。然而，使用该体外系统发现UAG是GHS-R的完全激动剂，其半数有效浓度（EC(50)）在1.6至2 microM之间。相应地，UAG以13 microM的半数抑制浓度（IC(50)）从GHS-R上取代放射性标记的胃饥饿素。此外还发现GHS-R拮抗剂阻断UAG诱导的Ca(2+)的效力与其对胃饥饿素激活GHS-R的作用大致相似，表明作用方式相似。这些研究结果在一个明确的系统中证明，UAG不会拮抗胃饥饿素对GHS-R的激活。但我们的研究结果也强调了在旨在研究GHS-R非依赖性效应的体外和体内实验系统中评估所用UAG浓度的重要性。在UAG的局部浓度可能达到高纳摩尔至微摩尔范围时，对GHS-R非依赖性效应的判定应谨慎进行
