Enyeart Judith A, Danthi Sanjay J, Enyeart John J
Dept. of Neuroscience, College of Medicine and Public Health, The Ohio State University, 5196 Graves Hall, 333 W.10th Ave, Columbus, OH 43210-1239, USA.
Am J Physiol Endocrinol Metab. 2004 Dec;287(6):E1154-65. doi: 10.1152/ajpendo.00223.2004. Epub 2004 Aug 17.
Bovine adrenal glomerulosa (AZG) cells were shown to express bTREK-1 background K(+) channels that set the resting membrane potential and couple angiotensin II (ANG II) receptor activation to membrane depolarization and aldosterone secretion. Northern blot and in situ hybridization studies demonstrated that bTREK-1 mRNA is uniformly distributed in the bovine adrenal cortex, including zona fasciculata and zona glomerulosa, but is absent from the medulla. TASK-3 mRNA, which codes for the predominant background K(+) channel in rat AZG cells, is undetectable in the bovine adrenal cortex. In whole cell voltage clamp recordings, bovine AZG cells express a rapidly inactivating voltage-gated K(+) current and a noninactivating background K(+) current with properties that collectively identify it as bTREK-1. The outwardly rectifying K(+) current was activated by intracellular acidification, ATP, and superfusion of bTREK-1 openers, including arachidonic acid (AA) and cinnamyl 1-3,4-dihydroxy-alpha-cyanocinnamate (CDC). Bovine chromaffin cells did not express this current. In voltage and current clamp recordings, ANG II (10 nM) selectively inhibited the noninactivating K(+) current by 82.1 +/- 6.1% and depolarized AZG cells by 31.6 +/- 2.3 mV. CDC and AA overwhelmed ANG II-mediated inhibition of bTREK-1 and restored the resting membrane potential to its control value even in the continued presence of ANG II. Vasopressin (50 nM), which also physiologically stimulates aldosterone secretion, inhibited the background K(+) current by 73.8 +/- 9.4%. In contrast to its potent inhibition of bTREK-1, ANG II failed to alter the T-type Ca(2+) current measured over a wide range of test potentials by using pipette solutions of identical nucleotide and Ca(2+)-buffering compositions. ANG II also failed to alter the voltage dependence of T channel activation under these same conditions. Overall, these results identify bTREK-1 K(+) channels as a pivotal control point where ANG II receptor activation is transduced to depolarization-dependent Ca(2+) entry and aldosterone secretion.
研究表明，牛肾上腺球状带（AZG）细胞表达bTREK-1背景钾通道，该通道设定静息膜电位，并将血管紧张素II（ANG II）受体激活与膜去极化及醛固酮分泌相偶联。Northern印迹和原位杂交研究显示，bTREK-1 mRNA在牛肾上腺皮质中均匀分布，包括束状带和球状带，但髓质中不存在。编码大鼠AZG细胞中主要背景钾通道的TASK-3 mRNA在牛肾上腺皮质中无法检测到。在全细胞电压钳记录中，牛AZG细胞表达一种快速失活的电压门控钾电流和一种非失活的背景钾电流，其特性共同表明它为bTREK-1。外向整流钾电流可被细胞内酸化、ATP以及bTREK-1开放剂（包括花生四烯酸（AA）和肉桂基1-3,4-二羟基-α-氰基肉桂酸酯（CDC））的灌流激活。牛嗜铬细胞不表达这种电流。在电压钳和电流钳记录中，ANG II（10 nM）选择性抑制非失活钾电流82.1±6.1%，并使AZG细胞去极化31.6±2.3 mV。即使在持续存在ANG II的情况下，CDC和AA也能克服ANG II介导的对bTREK-1的抑制，并将静息膜电位恢复到对照值。血管加压素（50 nM）在生理上也刺激醛固酮分泌，它抑制背景钾电流73.8±9.4%。与对bTREK-1的强效抑制相反，在使用相同核苷酸和钙缓冲成分的移液管溶液在广泛的测试电位范围内测量时，ANG II未能改变T型钙电流。在相同条件下，ANG II也未能改变T通道激活的电压依赖性。总体而言，这些结果表明bTREK-1钾通道是一个关键控制点，ANG II受体激活在此处被转导为去极化依赖性钙内流和醛固酮分泌。
