CELLULAR AND SUBCELLAR CALCIUM ION HOMEOSTASIS

该项目的重点是细胞实现体内平衡的机制， 钙离子浓度，无论是在胞质溶胶和其他细胞 隔室，并允许响应激素和钙的变化， 神经传递素 今年我们利用了 膜永久荧光钙离子螯合剂，以测量 心肌细胞悬液中线粒体内游离钙浓度 线粒体，并与心脏功能科合作， 在单个心肌细胞中原位。 在分离线粒体的研究中， 我们测量了钙离子穿过的浓度梯度 线粒体膜，相对于不同的线粒体外 钙以及跨膜pH梯度的变化， 其为钙从线粒体流入提供驱动力。 在模拟的生理条件下，即，存在下 钠和镁离子的胞浆浓度，呼吸 线粒体显示维持负钙梯度（内部 除以外部），当线粒体外钙小于500 nM时： 在高于此值时，线粒体钙浓度 梯度变为正。 线粒体内的协同研究 在单个活细胞中原位的钙是相当新颖的，并且已经表明， 该参数位于先前所示的范围内 线粒体内脱氢酶活性。 此外，线粒体内 游离钙上升，响应β-肾上腺素能刺激，并增加 电刺激率，增强工作输出的情况下， 细胞，因此需要更活跃的氧化磷酸化， 线粒体

This project focuses on the mechanism whereby cells achieve homeostasis of calcium ion concentration, both within the cytosol and other cellular compartments, and allow changes in calcium in response to hormones and neurotransmitters. This year we have taken advantage of the availability of membrane-permanent fluorescent calcium ion-chelating agents to measure intramitochondrial free calcium concentrations both in suspensions of heart mitochondria and, in a collaboration with the Cardiac Function Section, in situ in a single cardiac myocyte. In the work with isolated mitochondrial membrane we have measured the concentration gradient of calcium ions across the mitochondrial membrane, with respect to varying extramitochondrial calcium and also with respect to changes in the transmembrane pH gradient, which provides the driving force for calcium afflux from the mitochondria. Under simulated physiological conditions, i.e., in the presence of cytosolic concentrations of sodium and magnesium ions, respiring mitochondria were shown to maintain a negative calcium gradient (inside divided by outside) when extramitochondrial calcium was less than 500 nM: at higher values than this, the mitochondrial calcium concentration gradient becomes positive. The collaborative studies on intramitochondrial calcium in situ in a single living cell are quite novel and have shown that this parameter lies within the range previously shown to modulate intramitochondrial dehydrogenase activity. Further, intramitochondiral free calcium rises in response to beta-adrenergic stimulation and increased rate of electrical stimulation, situations which enhance work output by the cell and thus require more active oxidative phosphorylation by the mitochondria.