Lee Andy K, Tse Amy
9-70 Medical Sciences Building, Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Endocrinology. 2005 Nov;146(11):4985-93. doi: 10.1210/en.2005-0358. Epub 2005 Aug 4.
The rise in cytosolic free Ca2+ concentration ([Ca2+]i) is the major trigger for secretion of ACTH from pituitary corticotropes. To better understand the shaping of the Ca2+ signal in corticotropes, we investigated the mechanisms regulating the depolarization-triggered Ca2+ signal using patch-clamp techniques and indo-1 fluorometry. The rate of cytosolic Ca2+ clearance was unaffected by inhibitors of Na+/Ca2+ exchanger or plasma membrane Ca2+-ATPase (PMCA), slightly slowed by sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) inhibitor, but dramatically slowed by mitochondrial uncouplers or inhibitor of mitochondrial uniporter. Measurements with rhod-2 revealed that depolarization-triggered increase in mitochondrial Ca2+ concentration. Thus, mitochondria have a dominant role in cytosolic Ca2+ clearance. Using the Mn2+ quench technique, we found the presence of a continuous basal Ca2+ influx in corticotropes. This basal Ca2+ influx was balanced by the combined actions of mitochondrial uniporter and PMCA and SERCA pumps. Inhibition of the mitochondrial uniporter or PMCA or SERCA pumps elevated basal [Ca2+]i. Using membrane capacitance measurement, we found that the change in the shape of the depolarization-triggered Ca2+ signal after mitochondrial inhibition was associated with enhancement of the exocytotic response. Thus, mitochondria have a dominant role in the regulation of Ca2+ signal and exocytosis in corticotropes.
胞质游离钙离子浓度（[Ca2+]i）的升高是垂体促肾上腺皮质激素细胞分泌促肾上腺皮质激素（ACTH）的主要触发因素。为了更好地理解促肾上腺皮质激素细胞中Ca2+信号的形成，我们使用膜片钳技术和indo-1荧光测定法研究了调节去极化触发的Ca2+信号的机制。胞质Ca2+清除率不受Na+/Ca2+交换体或质膜Ca2+-ATP酶（PMCA）抑制剂的影响，受肌浆内质网Ca2+-ATP酶（SERCA）抑制剂的影响略有减慢，但受线粒体解偶联剂或线粒体单向转运体抑制剂的影响则显著减慢。用rhod-2测量显示，去极化触发线粒体Ca2+浓度升高。因此，线粒体在胞质Ca2+清除中起主导作用。使用Mn2+淬灭技术，我们发现在促肾上腺皮质激素细胞中存在持续的基础Ca2+内流。这种基础Ca2+内流通过线粒体单向转运体与PMCA和SERCA泵的联合作用得以平衡。抑制线粒体单向转运体或PMCA或SERCA泵会升高基础[Ca2+]i。通过膜电容测量，我们发现线粒体抑制后去极化触发的Ca2+信号形状的变化与胞吐反应的增强有关。因此，线粒体在促肾上腺皮质激素细胞中Ca2+信号和胞吐作用的调节中起主导作用。
