Properties of Ion Channels that Control Secretion

控制分泌的离子通道的特性

• 批准号: 7097929
• 负责人: JOHN J ENYEART
• 金额: $ 27.45万
• 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 2009-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7097929
• 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

DESCRIPTION (provided by applicant): The adrenal cortex of mammals is divided into an outer glomerulosa and inner fasciculata that secrete different corticosteroid hormones, including the mineralocorticoid aldosterone and the glucocorticoid cortisol. These hormones function critically in regulating electrolyte, water, and energy balance, and are therefore vital for maintaining blood pressure and plasma glucose within normal limits. Precise control of blood glucose by cortisol is essential because this sugar is the brain's primary energy source. Hypoglycemia rapidly leads to brain damage and death. Aberrant secretion of corticosteroids causes endocrine pathology, including Cushing's and Addison's diseases. At the cellular level, cortisol secretion by adrenal zona fasciculata (AZF) cells is controlled primarily by the pituitary peptide ACTH, while zona glomerulosa (AZG) cells secrete aldosterone in response to the peripheral peptide Angiotensin II (All). Although many of the physiological stimuli and intracellular messengers that regulate secretion of corticosteroids have been identified, the signaling pathways that link these stimuli to secretion are incompletely understood. In particular, the role of electrical activity and specific ion channels in the secretion of corticosteroids has not been clarified. Bovine AZF and AZG cells express several ion channels that determine their electrical properties and the ionic events involved in secretion. The K+ channel bTREK-1 sets the resting potential, is activated by ATP and inhibited by ACTH and All. Thus, TREK-1 channels act pivotally in integrating hormonal and metabolic signals and coupling these to depolarization-dependent calcium (Ca2+) entry and secretion. A specific model has been developed for ACTH- and All-stimulated cortisol and aldosterone secretion that depends on the generation of Ca2+-dependent action potentials. Specifically, the inhibition of bTREK-1 K+ channels by ACTH and All leads to action potentials driven by opposing voltage-gated Ca2+ and K+ currents. Experiments described in this proposal test this hypothesis and identify signaling pathways that control function and expression of adrenocortical ion channels. Specific Aims will be: 1) To demonstrate that All inhibits bTREK-1 K+ channels in bovine AZF and AZG cells by separate Ca2+ - and ATP hydrolysis-dependent signaling pathways, and to identify their molecular mechanisms. To demonstrate that bTREK-1 channels set the resting potential of bovine AZG cells and that inhibition of these channels by All is coupled to depolarization-dependent aldosterone secretion; 2) To demonstrate that ACTH exerts short and long term control over the electrical properties of bovine AZF cells by regulating both the function and expression of AZF cell ion channels and to characterize the molecular mechanisms involved; and 3) To determine whether the ATP sensitivity of native bTREK-1 channels allows them to function as sensors whose activity varies with the plasma glucose concentration and the metabolic state of the AZF cell.

描述（由申请人提供）：哺乳动物的肾上腺皮质分为外肾小球和内束状体，它们分泌不同的皮质类固醇激素，包括盐皮质激素醛固酮和糖皮质激素皮质醇。这些激素在调节电解质、水和能量平衡方面起着关键作用，因此对于维持血压和血糖在正常范围内至关重要。皮质醇对血糖的精确控制至关重要，因为这种糖是大脑的主要能量来源。低血糖会迅速导致脑损伤和死亡。皮质类固醇的异常分泌引起内分泌病理学，包括库欣病和阿狄森病。 在细胞水平上，肾上腺束状体（AZF）细胞的皮质醇分泌主要由垂体肽ACTH控制，而肾小球（AZG）细胞响应于外周肽血管紧张素II（All）分泌醛固酮。虽然已经确定了许多调节皮质类固醇分泌的生理刺激和细胞内信使，但将这些刺激与分泌联系起来的信号通路尚未完全了解。特别是，电活动和特定离子通道在皮质类固醇分泌中的作用尚未阐明。 牛AZF和AZG细胞表达几种离子通道，这些离子通道决定了它们的电特性和分泌中涉及的离子事件。K+通道bTREK-1设置静息电位，由ATP激活并由ACTH和All抑制。因此，TREK-1通道在整合激素和代谢信号并将这些信号与去极化依赖性钙（Ca 2+）进入和分泌偶联中起关键作用。 一个特定的模型已经开发的ACTH和所有刺激的皮质醇和醛固酮分泌依赖于产生的钙离子依赖性动作电位。具体而言，ACTH和All对bTREK-1 K+通道的抑制导致由相反的电压门控Ca 2+和K+电流驱动的动作电位。本提案中描述的实验验证了这一假设，并确定了控制肾上腺皮质离子通道功能和表达的信号通路。具体目标是：1）证明All通过单独的Ca 2+和ATP水解依赖性信号通路抑制牛AZF和AZG细胞中的bTREK-1 K+通道，并鉴定其分子机制。证明bTREK-1通道设定牛AZF细胞的静息电位，并证明A11对这些通道的抑制与去极化依赖的醛固酮分泌有关：2）证明ACTH通过调节AZF细胞离子通道的功能和表达对牛AZF细胞的电特性进行短期和长期的控制，并描述相关的分子机制;和3）确定天然bTREK-1通道的ATP敏感性是否允许它们作为其活性随血浆葡萄糖浓度和AZF细胞的代谢状态而变化的传感器起作用。