Villalobos Carlos, Nuñez Lucía, Montero Mayte, García Antonio G, Alonso Maria Teresa, Chamero Pablo, Alvarez Javier, García-Sancho Javier
Instituto de Biología y Genética Molecular, Universidad de Valladolid y Consejo Superior de Investigaciones Científicas, Departamento de Fisiología y Bioquímica, Facultad de Medicina, E-47005 Valladolid, Spain..
FASEB J. 2002 Mar;16(3):343-53. doi: 10.1096/fj.01-0630com.
Recent results indicate that Ca2+ transport by organella contributes to shaping Ca2+ signals and exocytosis in adrenal chromaffin cells. Therefore, accurate measurements of [Ca2+] inside cytoplasmic organella are essential for a comprehensive analysis of the Ca2+ redistribution that follows cell stimulation. Here we have studied changes in Ca2+ inside the endoplasmic reticulum, mitochondria, and nucleus by imaging aequorins targeted to these compartments in cells stimulated by brief depolarizing pulses with high K+ solutions. We find that Ca2+ entry through voltage-gated Ca2+ channels generates subplasmalemmal high [Ca2+]c domains adequate for triggering exocytosis. A smaller increase of [Ca2+]c is produced in the cell core, which is adequate for recruitment of the reserve pool of secretory vesicles to the plasma membrane. Most of the Ca2+ load is taken up by a mitochondrial pool, M1, closer to the plasma membrane; the increase of [Ca2+]M stimulates respiration in these mitochondria, providing local support for the exocytotic process. Relaxation of the [Ca2+]c transient is due to Ca2+ extrusion through the plasma membrane. At this stage, mitochondria release Ca2+ to the cytosol through the Na+/Ca2+ exchanger, thus maintaining [Ca2+]c discretely increased, especially at core regions of the cell, for periods that outlast the duration of the stimulus.
近期研究结果表明，细胞器的钙离子转运有助于塑造肾上腺嗜铬细胞中的钙离子信号和胞吐作用。因此，精确测量细胞质细胞器内的钙离子浓度对于全面分析细胞受刺激后的钙离子重新分布至关重要。在此，我们通过对靶向这些细胞器的水母发光蛋白进行成像，研究了在高钾溶液短暂去极化脉冲刺激下细胞内质网、线粒体和细胞核内钙离子的变化。我们发现，通过电压门控钙离子通道进入的钙离子会在质膜下产生足以触发胞吐作用的高钙离子浓度区域。细胞核心区域的钙离子浓度升高幅度较小，这足以将分泌囊泡的储备池募集到质膜。大部分钙离子负载被靠近质膜的线粒体池M1摄取；线粒体中钙离子浓度的升高会刺激这些线粒体的呼吸作用，为胞吐过程提供局部支持。细胞质钙离子瞬变的弛豫是由于钙离子通过质膜挤出。在此阶段，线粒体通过钠/钙交换器将钙离子释放到细胞质中，从而使细胞质钙离子浓度持续离散升高，尤其是在细胞的核心区域，其持续时间超过刺激持续时间。
