Visualization of the mitochondria ofToxoplasma gondii-infected mouse fibroblasts by the cationic permeant fluorescent dye rhodamine 123

Summary The mitochondria of living mouse fibroblasts infected withToxoplasma gondii were monitored with the cationic permeant fluorescent dye rhodamine 123. Fluorescence microscopy revealed that host cell mitochondria accumulated at the cytoplasmic surface of parasitophorous vacuoles and increased the dye uptake in the periparasitophorous vacuole asT. gondii multiplied.The author wishes gratefully to acknowledge the work of Miss Mayumi Kato and Mr. Isao Kimata in preparing the photographs. The publication cost was supported by a grant of the Ohyama Health Foundation.     

Calcium and sodium distribution and movements in smooth muscle

Summary Electron probe microanalysis (EPMA) has been used to study the subcellular distribution of Ca, Na, K. Cl, and Mg in smooth muscle. The EPMA results indicate that the sarcoplasmic reticulum (SR) is the majorintracellular source and sink of activator Ca: norepinephrine decreases the Ca content of the junctional SR in portal vein smooth muscle. Mitochondria do not play a significant role in regulating cytoplasmic free Ca²⁺, but mitochondrial Ca content can be altered to a degree compatible with suggestions that fluctuations in matrix Ca contribute to the control of mitochondrial metabolism. The rise intotal cytoplasmic Ca during a maintained, maximal contraction is very much greater than the rise in free Ca²⁺, and is probably in excess of the known binding sites available on calmodulin and myosin. Cell Ca is not increased in normal cells that are Na-loaded. The non-Donnan distribution of Cl is not due to compartmentalization, but reflects high cytoplasmic Cl. Na-loading of smooth muscle in K-free solutions is temperature dependent, and may exhibit cellular heterogeneity undetected by conventional techniques. The total cell Mg is equivalent to approximately 12 mM, and less than 50% of it can be accounted for by binding to ATP and to actin. Mitochondrial monovalent cations in smooth muscle are relatively rapidly exchangeable.     

Molecular identification and phylosenetic position of Cuora yunnanensis

The Yunnan box turtle （Cuora yunnanensis, Boulenger, 1906）, which has drawn much attention in conservation biology, was regarded as extinct since it was previously known only from 12 specimens collected in Yunnan, China, before 1908. Recently, live specimens have been discovered which are suggested to be C. yunnanensis. To determine whether the newly discovered specimens are really C. yunnanensis, we have established a molecular phylogeny, with a 1725-bp fragment of mitochondrial DNA, using samples from three live individuals of C. yunnanensis, together with sequence data from a museum specimen of C. yunnanensis （MNHN 1907.10） and other members of the genus Cuora. We found that the three newly discovered individuals and the old museum specimen of C. yunnanensis are very similar both in morphology and in mitochondrial DNA sequence, suggesting that the three new individuals are the very C. yunnanensis, and thus the species is not extinct. Our phylogenetic analysis also demonstrates that C. yunnanensis is not of recent hybrid origin, but rather represents a distinct evolutionary lineage.     

星形胶质细胞线粒体作为缺血性脑卒中治疗靶点的探讨

缺血性脑卒中是中老年常见的急性脑血管病,是当今世界主要的致死性疾病之一。现有治疗方案有限,仅适用于一小部分中风患者。因此,开发有效的治疗方法以减少脑损伤至关重要。星形胶质细胞(astrocyte, AS)是中枢神经系统的核心组成部分,其线粒体功能障碍是缺血性脑卒中的初始事件,在神经元存活和神经功能改善过程中发挥着重要作用。以AS细胞线粒体在缺血性脑卒中发病中的作用机制为切入点,分析讨论了缺血性脑卒中发生时AS细胞线粒体的生物能量与动力学变化、细胞之间线粒体的转移以及AS细胞线粒体对脑血流的调节作用,提出将AS细胞线粒体作为治疗缺血性脑卒中的靶点之一,以更好地了解AS细胞线粒体在缺血诱导的神经元死亡过程中的重要作用,为缺血性脑卒中的新型治疗方案提供理论基础。     

真核生物DNA连接酶Ⅲ的功能演化

DNA连接酶Ⅲ被认为只存在于脊椎动物,并在细胞核DNA的修复和线粒体DNA的复制和修复过程中发挥功能.虽然近来有关于无脊椎动物中存在着DNA连接酶Ⅲ的报道,但其功能演化及在无脊椎动物中的分布仍不清楚.为进一步探讨DNA连接酶Ⅲ的功能演化,进行了数据库搜索、线粒体定位信号(MLS)预测和功能位点保守性分析等.研究结果显示:DNA连接酶Ⅲ在变形虫、动物界和领鞭毛虫中广泛存在,但其在真菌界等发生整个蛋白或部分结构域的丢失;很多物种的DNA连接酶Ⅲ不含线粒体定位信号,因此,它们不太可能在线粒体中发挥作用,而参与细胞核DNA的修复是DNA连接酶Ⅲ较为古老和保守的功能.     

线粒体膜间隙蛋白质释放与细胞凋亡研究进展

近年来,国内外有关线粒体和肿瘤的关系研究的越来越多,开发与线粒体相关的新型药物并诱导肿瘤细胞凋亡逐渐成为热点.该文主要综述了近年来关于几种线粒体膜间隙蛋白质在细胞凋亡中的作用和由线粒体中释放的可能机制及其在肿瘤药物治疗中的最新进展,指出线粒体膜间隙蛋白质在诱导肿瘤细胞凋亡中具有重要作用.     

Evidence of undiscovered cell regulatory mechanisms: phosphoproteins and protein kinases in mitochondria

The finding that mitochondria contain substrates for protein kinases lead to the discovery that protein kinases are located in the mitochondria of certain tissues and species. These include pyruvate dyhydrogenase kinase, branched-chain α-ketoacid dehydrogenase kinase, protein kinase A, protein kinase Cδ, stress-activated kinase and A-Raf as well as unidentified kinases. Recent evidence suggests that mitochondrial protein kinases may be involved in physiological processes such as apoptosis and steroidogenesis. Additionally, the novel finding of low-molecular-weight GTP-binding proteins in mitochondria suggests the possibility that these may interact with mitochondrial protein kinases to regulate the activity of mitochondrial effector proteins. The fact that there are components of cellular regulatory systems in mitochondria indicates the exciting possibility of undiscovered systems regulating mitochondrial physiology. Received 19 June 2001; received after revision 7 August 2001; accepted 8 August 2001     

Low allozyme and mtDNA variability in the island endemic speciesDrosophila sechelia (D. melanogaster complex)

Summary Genetic variability ofD. sechellia is investigated at both mitochondrial and nuclear levels. The results reveal the existence of a single main type of mtDNA with very few variants and a very low enzyme polymorphism. This situation is consistent with the small population size of this specialized species.     

Cell size of mammalian myocardia is not related to physiological demand

Morphological characteristics of myocardial ventricular myocytes have been evaluated from 5 mammalian orders with resting heart rates ranging from 51 to 475 bpm. The purpose was to determine if morphological characteristics of the myocardia are related to the functional demand imposed on the cell as represented by the resting heart rate. Cell size is a constant among mammals of different sizes which have different physiological demands. In contrast, there is more mitochondrial area and less myofibrillar area per cell in animals with rapidly beating hearts than in animals with slower heart rates. Additionally, the mean cross sectional area of individual myofibrils is 30% larger in the cow as compared to the mouse. These findings combined with our previous studies indicate that the different functional requirements of myocardia from different mammalian orders are satisfied by intracellular adaptations of both a structural and biochemical nature.