Xia S L, Fain G L, Farahbakhsh N A
Department of Physiological Science, University of California, Los Angeles 90095-1527, USA.
Exp Eye Res. 1997 Apr;64(4):627-35. doi: 10.1006/exer.1996.0269.
The purpose of these experiments was to demonstrate the presence of somatostatin receptors on the nonpigmented epithelial cells of the rabbit ciliary body and their link with intracellular Ca2+ homeostasis. Freshly excised rabbit ciliary processes and nonpigmented cell layer, explants were loaded with the fluorescent dye fura-2, and free-Ca2+ concentration ([Ca2+]i) in the nonpigmented cells was measured with fluorescence ratio imaging. The cells were continuously perfused, and drugs were added to the perfusate. Somatostatin-14 (SS14, 0.1-1.0 microM) or acetylcholine (ACh, 10 microM) applied alone produced small increases in [Ca2+]i. However, SS14 (0.1 microM) in combination with ACh (10 microM) induced a massive increase in [Ca2+]i (25.7 +/- 3.3 times the baseline level, n = 28). The dose-response curve for SS14 (in the presence of 10 microM ACh) was sigmoidal with an EC50 of 3.9 nM and Hill coefficient of 2.5, indicating the requirement for multiple SS receptor activation. Somatostatin-28 could mimic the effect of SS14, although a much higher concentration was required. Shifting the SS14 dose-response curve to the right by about two-orders of magnitude resulted in a fit to the SS28 data. The response to ACh + SS14 could not be blocked by the alpha 2-adrenergic blocker yohimbine (Yoh, 10 microM) or the A1-specific adenosinergic antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 1 microM). Incubation of the tissue with pertussis toxin (PTx, 1 microgram ml-1) did not alter the response to ACh alone but eliminated the synergistic effect of somatostatin. We conclude that nonpigmented epithelial cells of the rabbit ciliary body possess a novel somatostatin receptor whose activation can synergistically potentiate the rise in [Ca2+]i produced by ACh. This potentiation appears to occur via a pertussis-toxin-sensitive pathway, perhaps through Gi.
这些实验的目的是证明兔睫状体无色素上皮细胞上生长抑素受体的存在及其与细胞内钙离子稳态的联系。将新鲜切除的兔睫状体突和无色素细胞层外植体用荧光染料fura-2加载，并用荧光比率成像法测量无色素细胞内的游离钙离子浓度（[Ca2+]i）。细胞持续灌注，并向灌注液中加入药物。单独应用生长抑素-14（SS14，0.1 - 1.0微摩尔）或乙酰胆碱（ACh，10微摩尔）可使[Ca2+]i出现小幅升高。然而，SS14（0.1微摩尔）与ACh（10微摩尔）联合应用可诱导[Ca2+]i大幅升高（为基线水平的25.7±3.3倍，n = 28）。SS14（在10微摩尔ACh存在下）的剂量反应曲线呈S形，EC50为3.9纳摩尔，希尔系数为2.5，表明需要多个SS受体激活。生长抑素-28可模拟SS14的作用，尽管需要更高的浓度。将SS14剂量反应曲线向右移动约两个数量级可与SS28数据拟合。α2-肾上腺素能阻滞剂育亨宾（Yoh，10微摩尔）或A1特异性腺苷能拮抗剂8-环戊基-1,3-二丙基黄嘌呤（DPCPX，1微摩尔）不能阻断对ACh + SS14的反应。用百日咳毒素（PTx，1微克/毫升）孵育组织不会改变对单独ACh的反应，但会消除生长抑素的协同作用。我们得出结论，兔睫状体无色素上皮细胞拥有一种新型生长抑素受体，其激活可协同增强ACh引起的[Ca2+]i升高。这种增强作用似乎通过百日咳毒素敏感途径发生，可能是通过Gi。
