PROPERTIES OF A K+ CURRENT THAT CONTROLS SECRECTION

控制节流的 AK 电流的特性

• 批准号: 6041259
• 负责人: JOHN J ENYEART
• 金额: $ 16.03万
• 依托单位: OHIO STATE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 1995
• 资助国家: 美国
• 起止时间: 1995-09-13 至 2003-11-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6041259
• 关键词: G protein; adenosine triphosphate; adrenal glands; adrenocorticotropic hormone; angiotensin II; bioenergetics; biological signal transduction; cortisol; hormone regulation /control mechanism; leptin; molecular cloning; nucleic acid sequence; pituitary adrenal axis; potassium channel; secretion; tissue /cell culture; voltage /patch clamp

In mammals, adrenal zona fasciculata (AZF) cells secrete cortisol which acts on cells of the liver, muscle, and adipose tissue to enhance glucose synthesis and to promote the breakdown of fat and muscle proteins. Precise control of blood glucose concentration by cortisol and other hormones is critical because this sugar is the primary energy source for the brain. Hypoglycemia can cause brain damage or death. Aberrant corticosteroid secretion is responsible for Cushing's and Addison's diseases. Cortisol secretion is controlled primarily by the pituitary peptide ACTH. However, a number of other physiological factors, including Angiotensin II, leptin, nucleotides, epinephrine, and glucose act on AZF cells to regulate secretion of this hormone. While physiological stimuli that regulate cortisol secretion have been identified, the signalling pathways involved are not understood. Although, the release of many hormones is coupled to depolarization-dependent Ca+ entry, the function of specific ion channels in AZF cell secretion has not been clarified. Bovine AZF calls express a novel K+ current (I[AC]) that sets the resting potential while it is inhibited by ACTH, AII, and external ATP at concentrations identical to those that depolarize AZF cells and stimulate cortisol secretion. These channels are also directly activated by intracellular ATP. The Convergent inhibition of I[AC] by three G protein- coupled receptors and its activation by intracellular ATP suggest that this channel is a control point where hormonal and metabolic signals are integrated and transduced to permeability and membrane potential changes associated with cortisol secretion. A detailed characterization of this channel, and the signalling pathways that regulate its activity will be essential to an understanding of adrenal cortical physiology. Whole-cell and single channel patch clamp will be used to describe the modulation of I[AC] K+ channels by hormones and metabolic factors. The aims of the proposed research will be: (1) to determine whether I[AC] channel gating is coupled to an ATP hydrolysis cycle, allowing these channels to act as glucose sensors; (2) to determine whether other hormonal and paracrine factors which physiologically regulate cortisol secretion, also modulate I[AC] K+ channels; (3) to identify the molecular components of the signalling pathway by which ACTH inhibits I[AC]; and (4) to characterize the properties and distribution of I[AC] K+ channel cDNAs after cloning and expression in a eucaryotic cell line.

在哺乳动物中，肾上腺束状带(AZF)细胞分泌皮质醇，皮质醇作用于肝脏、肌肉和脂肪组织的细胞，促进葡萄糖的合成，促进脂肪和肌肉蛋白质的分解。皮质醇和其他激素对血糖浓度的精确控制至关重要，因为这种糖是大脑的主要能量来源。低血糖会导致脑损伤或死亡。皮质类固醇分泌异常是库欣和艾迪生疾病的原因。皮质醇的分泌主要由脑垂体肽ACTH控制。然而，许多其他生理因子，包括血管紧张素II、瘦素、核苷酸、肾上腺素和葡萄糖作用于AZF细胞来调节这种激素的分泌。虽然已经确定了调节皮质醇分泌的生理刺激，但涉及的信号通路尚不清楚。尽管许多激素的释放与依赖去极化的钙离子进入有关，但特殊离子通道在AZF细胞分泌中的作用尚不清楚。牛AZF信号表达一种新的K+电流(I[AC])，该电流设定静息电位，而ACTH、AII和外部ATP抑制该电流的浓度与去极化AZF细胞和刺激皮质醇分泌的浓度相同。这些通道也被细胞内的三磷酸腺苷直接激活。三种G蛋白偶联受体对I[AC]的趋同抑制和细胞内ATP的激活表明，这一通道是激素和代谢信号整合并传递到与皮质醇分泌相关的通透性和膜电位变化的控制点。对这一通道和调节其活动的信号通路的详细描述对于理解肾上腺皮质生理学是必不可少的。全细胞膜片钳和单通道膜片钳将用于描述激素和代谢因素对I[AC]K+通道的调节。拟议研究的目的将是：(1)确定I[AC]通道门控是否与ATP水解循环偶联，使这些通道成为葡萄糖感受器；(2)确定其他生理调节皮质醇分泌的激素和旁分泌因子是否也调节I[AC]K+通道；(3)确定ACTH抑制I[AC]K+通道的信号通路的分子组成；以及(4)鉴定克隆并在真核细胞中表达后I[AC]K+通道cDNA的性质和分布。