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 由肽类激素包括促肾上腺皮质激素控制 （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，以增强葡萄糖 并促进脂肪和蛋白质的分解。异常 皮质类固醇分泌导致严重的病理， 库欣氏病和艾迪生氏病。盐皮质激素醛固酮 以维持体液和电解质平衡。不适当的醛固酮 分泌物表现为低血压或高血压。 肽类激素调节皮质类固醇激素的细胞机制 分泌物是不了解的。在许多分泌细胞中， 通过激活电压门控的 Ca 2+通道牛肾上腺皮质细胞具有一种新的钾离子通道 (IAC)来设定这些细胞的膜电位。重要的是，两者 ACTH和AII抑制IAC和去甲肾上腺素细胞的作用相当 亚纳摩尔浓度。这些化合物对IAC的会聚抑制作用 两种肽暗示了一种生理机制， 细胞膜上的信号可以与去极化依赖的 Ca 2+内流和类固醇激素分泌。 因为IAC似乎在传递生化信号中起着关键作用， 与分泌有关的电事件， 这种电流的基础通道和信号通路， 调节IAC活性对于了解肾上腺皮质 physiology. 在拟定的研究中，牛和人肾上腺束状核中的IAC 将用膜片电压钳技术检查细胞。功能 IAC在非洲爪蟾卵母细胞中的表达将用于克隆IAC通道 cDNA。拟议研究的目标是： 1)为了表征IAC的生物物理特性， 药理学，以及代谢因子和酶的调节; 2)识别和表征信号通路和分子 ACTH抑制IAC的机制; 3)为了确定IAC是否存在并受AII和ACTH调节， 人肾上腺皮质细胞; 4）克隆IAC的cDNA并测序， 在非洲爪蟾卵母细胞中表达克隆。

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.