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Localization and physiological functions of SRIF receptor and GHRH receptor in the rat pituitary

SRIF受体和GHRH受体在大鼠垂体的定位及生理功能

基本信息

批准号：
08680872
负责人：
KATO Masakatsu
金额：
$ 1.47万
依托单位：
Nippon Medical School
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

项目摘要

In the present research, we analyzed the effects of somatostatin (SRIF) and growth hormone releasing hormone (GHRH) on male rat pituitary cells in primary culture. Among pituitary cells we focused somatotrophs and folliculo-stellate cells.First, we analyzed the effects of these peptides on somatotrophs by a perforated patch clamp method and revealed following things. GHRH augmented the voltage-gated sodium current. In addition, GHRH elicited persistent sodium current at the potential more positive than-60mV.The former current was completely blocked by tetrodotoxin, whereas the latter current was not affected by that. On the other hand, SRIF had no effect on the voltage-gated sodium current, while that attenuated the GHRH-induced persistent sodium current. These results indicate (i) that GHRH augments basal GH secretion by facilitating the voltage-gated sodium current ; (ii) that GHRH-induced sodium current depolarizes somatotrophs which activates the voltage-gated calcium current, whereby facilitating GH secretion ; (iii) SRIF suppresses GH secretion not only by activating the inward rectifier potassium current but also attenuating the GHRH-induced sodium current.Second, we analyzed the effects of these peptides on folliculo-stellate cells by the method of calcium-imaging, GHRH affects intracellular calcium concentration ([Ca^<2+>]i) in 30% of cells in the total examined. Among responding cells, 95% of them responded to GHRH by augmenting [Ca^<2+>]i and remaining cells by suppressing [Ca^<2+>]i. Both responses were blocked by removing calcium from extracellular solution. SRIF suppressed the GHRH-induced responses in 70% of the cells without affecting remaining 30% of the cells. These results indicate that a substantial proportion of folliculo-stellate cells possesses the receptors for GHRH and SRIF and that the peptides regulate their function.

在本研究中，我们分析了生长抑素（SRIF）和生长激素释放激素（GHRH）对原代培养的雄性大鼠垂体细胞的影响。在垂体细胞中，我们重点关注生长激素细胞和滤泡星状细胞。首先，我们通过穿孔膜片钳方法分析了这些肽对生长激素细胞的影响，并揭示了以下内容。 GHRH 增强了电压门控钠电流。另外，GHRH在大于-60mV的正电位处引发持续的钠电流。前者的电流被河鲀毒素完全阻断，而后者的电流则不受河鲀毒素的影响。另一方面，SRIF 对电压门控钠电流没有影响，但会减弱 GHRH 诱导的持续钠电流。这些结果表明 (i) GHRH 通过促进电压门控钠电流来增强基础 GH 分泌； (ii) GHRH 诱导的钠电流使生长激素去极化，从而激活电压门控钙电流，从而促进 GH 分泌； (iii) SRIF不仅通过激活内向整流钾电流还通过减弱GHRH诱导的钠电流来抑制GH分泌。其次，我们通过钙成像的方法分析了这些肽对卵泡星状细胞的影响，GHRH影响了30%的受检细胞的细胞内钙浓度([Ca^<2+>]i)。在作出反应的细胞中，95％的细胞通过增加[Ca ^ 2+ ] i 来对GHRH作出反应，而其余细胞则通过抑制[Ca ^ 2+ ] i 来作出反应。通过从细胞外溶液中去除钙来阻止这两种反应。 SRIF 抑制了 70% 细胞中 GHRH 诱导的反应，而不影响其余 30% 的细胞。这些结果表明，相当大比例的滤泡星状细胞拥有 GHRH 和 SRIF 受体，并且这些肽调节其功能。