PROPERTIES OF A K+ CURRENT THAT CONTROLS SECRECTION

控制节流的 AK 电流的特性

• 批准号: 6329389
• 负责人: JOHN J ENYEART
• 金额: $ 16.51万
• 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/6329389
• 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，肾上腺束状体（AZF）细胞分泌皮质醇，其作用于肝脏、肌肉和脂肪组织的细胞以增强葡萄糖合成并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导致库欣病和阿狄森病的原因。皮质醇的分泌主要由垂体促肾上腺皮质激素控制。然而，许多其他生理因素，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细胞以调节该激素的分泌。虽然已经确定了调节皮质醇分泌的生理刺激，但所涉及的信号通路尚不清楚。尽管许多激素的释放与去极化依赖的Ca+内流相耦合，但特定离子通道在AZF细胞分泌中的功能尚未阐明。牛AZF细胞表达一种新的K+电流（I[AC]），该电流设置静息电位，同时被ACTH、AII和外部ATP抑制，其浓度与去甲肾上腺素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ATP直接激活。三种G蛋白偶联受体对I[AC]的会聚抑制及其被细胞内ATP激活表明，该通道是激素和代谢信号整合并转导为与皮质醇分泌相关的渗透性和膜电位变化的控制点。这个通道的详细特征，以及调节其活性的信号通路将是必不可少的肾上腺皮质生理学的理解。将使用全细胞和单通道膜片钳来描述激素和代谢因子对I[AC] K+通道的调节。本研究的目的是：（1）确定I[AC]通道门控是否与ATP水解循环偶联，使这些通道作为葡萄糖传感器;（2）确定生理上调节皮质醇分泌的其他激素和旁分泌因子是否也调节I[AC] K+通道;（3）鉴定ACTH抑制I[AC]的信号通路的分子组分;（4）在真核细胞系中克隆和表达后表征I[AC] K+通道cDNA的性质和分布。