PROPERTIES OF K+ CURRENT THAT CONTROLS SECRETION

在哺乳动物中，肾上腺细胞分泌的皮质类固醇是 由包括促肾上腺皮质激素在内的多肽激素控制 促肾上腺皮质激素(ACTH)和血管紧张素II(AII)。糖皮质激素，如皮质醇作用于 肝脏、肌肉和脂肪组织的细胞，以提高血糖 合成-并促进脂肪和蛋白质的分解。反常的 皮质类固醇分泌是导致严重病理的原因，包括 库欣和爱迪生的疾病。盐皮质激素的醛固酮作用 以维持液体和电解质的平衡。不适当的醛固酮 分泌物表现为低血压或高血压。 多肽激素调节皮质类固醇激素的细胞机制 分泌物是不被理解的。在许多分泌细胞中，荷尔蒙的产生 通过激活电压门控与膜去极化相耦合 CA2通道。牛肾上腺皮质细胞具有一种新的钾通道 (IAC)设置这些细胞的膜电位。重要的是，两者 ACTH和AII抑制IAC并使肾上腺细胞去极化 亚纳摩尔浓度。这些化合物对IAC的收敛抑制作用 两个肽暗示了一种生理机制，即生化 细胞膜上的信号可以耦合到依赖于去极化的 CA2进入和类固醇激素分泌。 因为IAC似乎在传递生化信号方面起着关键作用 对涉及分泌物的电事件进行了详细的表征 在这一电流中，潜在的通道和信号通路 调节Iac的活动对于理解肾上腺皮质是必不可少的 生理学。 在拟议的研究中，牛和人肾上腺束状带的IAC 细胞将用膜片电压钳技术进行检查。功能性 IAC在非洲爪哇卵母细胞中的表达将用于克隆IAC通道 CDNA.拟议研究的目的将是： 1)关于生物物理属性来表征IAC， 药理作用，代谢因子和酶的调节作用； 2)鉴定和表征信号通路和分子 ACTH抑制IAC的机制； 3)确定是否存在IAC，并受AII和ACTH的调节 人肾上腺皮质细胞；4)克隆IAC基因并测序 非洲爪哇卵母细胞的表达克隆。

In mammals, corticosteroid secretion by cells of the adrenal gland is controlled by peptide hormones including adrenocorticotropic hormone (ACTH) and angiotensin II (AII). Glucocorticoids such as cortisol act on cells of the liver, muscle and adipose tissue to enhance glucose synthesis-and to promote the breakdown of fat and proteins. Aberrant corticosteroid secretion is responsible for serious pathology including Cushing's and Addison's diseases. The mineralocorticoid aldosterone acts to maintain fluid and electrolyte balance. Inappropriate aldolsterone secretion is manifested as hypo- or hypertension. The cellular mechanisms by which peptide hormones regulate corticosteroid secretion are not understood. In many secretory cells, hormone production is coupled to membrane depolarization through activation of voltage-gated Ca2+ channels. Bovine adrenocortical cells possess a novel K+ channel (IAC) that sets the membrane potential of these cells. Importantly, both ACTH and AII inhibit IAC and depolarize adrenal cells at equivalent subnanomolar concentrations. The convergent inhibition of IAC by these two peptides suggests a physiological mechanism whereby biochemical signals at the cell membrane can be coupled to depolarization-dependent Ca2+ entry and steroid hormone secretion. Because IAC appears to act pivotally in transducing biochemical signals to electrical events involved in secretion, a detailed characterization of this current, the underlying channels and the signalling pathways that regulate IAC activity will be essential to understanding adrenal cortical physiology. In the proposed studies, IAC in bovine and human adrenal zona fasciculata cells will be examined with patch voltage clamp techniques. Functional expression of IAC in Xenopus oocytes will be used to clone IAC channel cDNA. The aims of the proposed research will be: 1) To characterize IAC with respect to biophysical properties, pharmacology, and modulation by metabolic factors and enzymes; 2) To identify and characterize the signalling pathways and molecular mechanisms by which ACTH inhibits IAC; 3) To determine whether IAC is present and regulated by AII and ACTH in human adrenocortical cells; 4) To clone and sequence the cDNA for IAC by expression cloning in Xenopus oocytes.