Endoplasmic reticulum derived decorated tubules in the sieve elements ofNymphaea

Summary Bundles of decorated tubules found in the sieve elements ofNymphaea have been studied with the transmission electron microscope. Comparatively straight tubules (100 nm in diameter) arise from the endoplasmic reticulum during early stages of sieveelement development and subsequently associate into bundles of up to 100 tubules that parallel the longitudinal cell axis. From the start of their formation the tubules are structurally distinct from other ER profiles due to their dense decoration with particles. High magnifications reveal an orderly array of the particles (about 24 surround a 100 nm tubule) and suggest a modification of their membrane so that it is no longer dissolvable into a regular three-layered structure. Later during sieve-element ontogeny the decorated tubules get invaginated by smooth ER membranes, thereby squeezing out the intratubular (extracytoplasmic) space. As a result a double mantle is formed that surrounds a plasmatic cylinder. Decorated 100 nm tubules with inner membranes are present in enucleate mature sieve elements ofNymphaea alba andN. tuberosa. Considerably larger tubules (about 200 nm in diameter) were found inN. Candida andN. tetragona and occasionally also inNuphar and Barclaya, two other genera from the same family. The decoration of the tubules and their subsequent invagination by smooth membranes are discussed with respect to the controlled autolysis of sieve elements.Dedicated to Prof. Dr. Dr. h.c. Eberhard Schnepf on the occasion of his retirement     

Variations in the kinetic response of several different phosphate-dependent glutaminase isozymes during acute metabolic acidosis

Summary We describe the kinetic modifications to mitochondrial-membrane-bound phosphate-dependent glutaminase in various types of rat tissue brought about by acute metabolic acidosis. The activity response of phosphate-dependent glutaminase to glutamine was sigmoidal, showing positive co-operativity, the Hill coefficients always being higher than 2. The enzyme from acidotic rats showed increased activity at subsaturating concentrations of glutamine in kidney tubules, as might be expected, but not in brain, intestine or liver tissues. Nevertheless, when brain and intestine from control rats were incubated in plasma from acutely acidotic rats enzyme activity increased at 1 mM glutamine in the same way as in kidney cortex. The enzyme from liver tissue remained unaltered. S_0.5 and n_H values decreased significantly in kidney tubules, enterocytes and brain slices preincubated in plasma from acidotic rats. The sigmoidal curves of phosphate-dependent glutaminase shifted to the left without any significant changes in V_max. The similar response of phosphate-dependent glutaminase to acute acidosis in the kidney, brain and intestine confirms the fact that enzymes from these tissues are kinetically identical and reaffirms the presence of an ammoniagenic factor in plasma, either produced or concentrated in the kidneys of rats with acute acidosis.Abbreviations Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulphonic acid - EDTA NN-1,2-Ethane-diylbis [N-(carboxymethyl)glycyne] - Tris 2-amino-2-hydroxymethyl-1,3-propanediol - PDG phosphate dependent glutaminase Publication No. 145 from Drogas, Tóxicos Ambientales y Metabolismo Celular Research Group. Department of Biochemistry and Molecular Biology, University of Granada, Spain     

The effect of infection with Dirofilaria immitis (dog heartworm) on fluid secretion rates in the Malpighian tubules of the mosquitoes Aedes taeniorhynchus and Anopheles quadrimaculatus

Dirofilaria immitis, the parasitic nematode causing the disease dog heartworm, is transmitted by female mosquitoes. During their development, larval nematodes reside in the cells of the Malpighian tubules of these mosquitoes for approx 13 days. We have examined the effect of the presence of these large intracellular parasites on the main physiological function of the Malpighian tubules, i.e. fluid secretion. Rates of fluid secretion were examined in vitro using both normal and infected tubules of the mosquito species Aedes taeniorhynchus and Anopheles quadrimaculatus. Tubules of A. quadrimaculatus show changes in trasport rate during the reproductive cycle. Those of A. taeniorhynchus do not. Infection with larvae of D. immitis had no effect on the rate of fluid secretion in tubules of A. quadrimaculatus. In A. taeniorhynchus by contrast, the tubules show decline in transport with time following infection. The reduction in transport capacity is proportional to the number of worms infecting the tubule. The present paper and separate ultrastructural studies demonstrate that parallel changes in microvillar ultrastructure and epithelial transport rates occur in response to infection by the parasite. In both species examined, the survival of the mosquitoes and their vector potential are determined by factors other than the transport capacities of the infected Malpighian tubules.     

Inositol trisphosphate and excitation-contraction coupling in skeletal muscle

The role of inositol trisphosphate as a chemical messenger in excitation-contraction coupling is discussed, both in terms of positive and negative results. The evidence presented includes experiments on the effect of inositol trisphosphate in intact and skinned fibers, in calcium release from isolated sarcoplasmic reticulum vesicles, in activation of single calcium release channels incorporated in planar bilayers, and biochemical experiments that have established the presence of all the intermediate steps involved in the metabolism of phosphoinositides, both in intact muscle and in isolated membranes. From these results, it is clear that a role for inositol triphosphate in skeletal muscle function is highly likely; whether this molecule is the physiological messenger in excitation-contraction coupling remains to be established.     

三种波段电磁辐射致大鼠睾丸损伤的比较

目的对比性探讨电磁脉冲(EMP)、S带高功率微波(S-HPM)和X带高功率微波(X-HPM)三种波段电磁辐射致睾丸组织受损的近期和远期效应及其相关敏感指标。方法雄性Wistar大鼠192只,随机分为EMP组、S-HPM组、X-HPM组和对照组,于照后不同时间点采集睾丸组织称重,光镜观察睾丸损伤,并用图像分析技术对曲细精管病变进行定量分析。结果三种波段电磁波辐照后睾丸结构和生精细胞形态损伤基本相似:早期睾丸重及睾丸重/体重比值呈下降趋势;曲细精管生精上皮变薄,生精细胞排列紊乱,精原细胞变性坏死并由管壁脱落,精母细胞和精子数量减少并团聚于管腔中央,支持细胞和间质细胞不同程度变性;曲细精管受损百分率显示EMP组最重,S-HPM最轻,生精细胞受损数量与程度显著增加(P0.05)。结论三种波段电磁辐射对睾丸生精细胞的损伤,具有速发性、时相性、分布不均一性特点;损伤程度呈EMPX-HPMS-HPM;睾丸曲细精管受损百分率可定量反映其损伤程度,可望成为评估电磁辐射致睾丸损伤的敏感指标之一。     

桃小食心虫幼虫的消化道和马氏管的显微结构观察

利用光学显微镜和扫描电子显微镜,在形态学和组织学水平上研究_『桃小食心虫 Carposina sasakii 幼虫消化道和屿氏管的结构.桃小食心虫幼虫消化道由前肠、中肠和后肠组成.前肠细短,肌肉层薄.前肠与中肠交界处有突出的胃盲囊.中肠长且粗大,内有围食膜,肠壁细胞较大,外层为发达的环肌和纵肌.后肠上皮细胞内陷很深.6根念珠状的马氏管位于中、后肠分界处.     

Underlying mechanism of the contractile dysfunction in atrophied ventricular myocytes from a murine model of hypothyroidism

Hypothyroidism (Hypo) is a risk factor for cardiovascular diseases, including heart failure. Hypo rapidly induces Ca²⁺ mishandling and contractile dysfunction (CD), as well as atrophy and ventricular myocytes (VM) remodeling. Hypo decreases SERCA-to-phospholamban ratio (SERCA/PLB), and thereby contributes to CD. Nevertheless, detailed spatial and temporal Ca²⁺ cycling characterization in VM is missing, and contribution of other structural and functional changes to the mechanism underlying Ca²⁺ mishandling and CD, as transverse tubules (T-T) remodeling, mitochondrial density (D_mit) and energy availability, is unclear. Therefore, in a rat model of Hypo, we aimed to characterize systolic and diastolic Ca²⁺ signaling, T-T remodeling, D_mit, citrate synthase (CS) activity and high-energy phosphate metabolites (ATP and phosphocreatine).We confirmed a decrease in SERCA/PLB (59%), which slowed SERCA activity (48%), reduced SR Ca²⁺ (19%) and blunted Ca²⁺ transient amplitude (41%). Moreover, assessing the rate of SR Ca²⁺ release (dRel/dt), we found that early and maximum dRel/dt decreased, and this correlated with staggered Ca²⁺ transients. However, dRel/dt persisted during Ca²⁺ transient relaxation due to abundant late Ca²⁺ sparks. Isoproterenol significantly up-regulated systolic Ca²⁺ cycling. T-T were unchanged, hence, cannot explain staggered Ca²⁺ transients and altered dRel/dt. Therefore, we suggest that these might be caused by RyR2 clusters desynchronization, due to diminished Ca²⁺-dependent sensitivity of RyR2, which also caused a decrease in diastolic SR Ca²⁺ leak. Furthermore, D_mit was unchanged and CS activity slightly decreased (14%), however, the ratio phosphocreatine/ATP did not change, therefore, energy deficiency cannot account for Ca²⁺ and contractility dysregulation. We conclude that decreased SR Ca²⁺, due to slower SERCA, disrupts systolic RyR2 synchronization, and this underlies CD.     

Rab11 is required for tubulogenesis of Malpighian tubules in Drosophila melanogaster

Intracellular vesicular trafficking is one of the important tools in maintaining polarity, adhesion, and shape of epithelial cells. Rab11, a subfamily of the Ypt/Rab gene family of ubiquitously expressed GTPases and a molecular marker of recycling endosomes, transports different components of plasma membrane. Here, we report that Rab11 affects tubulogenesis of Malpighian tubules (MTs). MTs are simple polarized epithelial tubular structures, considered as functional analogue of human kidney. Rab11 has pleiotropic effects on MTs development as down‐regulation of Rab11 in principal cells (PCs) of MTs from embryonic stages of development results in reduced endoreplication, clustering of cells, disorganized cytoskeleton, and disruption of polarity leading to shortening of MTs in third instar larvae. Rab11 is also required for proper localization of different transporters in PCs, essential for physiological activity of MTs. Collectively, our data suggest that Rab11 plays a key role in the process of tubulogenesis of MTs in Drosophila.