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71.
CHARACTERISTICS OF MEMBRANE TRANSPORT PROCESSES OF MACULA DENSA CELLS   总被引:1,自引:0,他引:1  
1. Macula densa (MD) cells are located within the thick ascending limb (TAL) and have their apical surface in contact with tubular fluid and their basilar region in contact with the glomerulus. These cells sense changes in luminal fluid sodium chloride concentration ([NaCl]) and transmit signals resulting in changes in vascular resistance (tubuloglomerular feedback) and renin release. 2. Current efforts have focused on understanding the cellular transport mechanisms of MD cells. Progress in this area has benefited from the use of the isolated perfused TAL-glomerular preparation, which permits direct access to MD cells. 3. Using microelectrodes to measure basolateral membrane potential (VBL) of MD cells, it was found that VBL was very sensitive to changes in luminal fluid [NaCl]. As [NaCl] was elevated from 20 to 150mmol/L, VBL was found to depolarize by over 30 mV. 4. Basolateral membrane potential measurements were also used to identify an apical Na+: 2CI?: K+ cotransport pathway in MD cells that is the major pathway for NaCl entry into these cells. 5. Other work identified a basolateral chloride channel that is presumed to be responsible for changes in VBL during alterations in luminal [NaCl]. This channel, which is the predominant conductance across the basolateral membrane, may be regulated by intracellular Ca2+ and cAMP. 6. An apical Na+: H+ exchanger in MD cells was detected by measuring changes in intracellular pH using the fluorescent probe 2′,7′-bis-(2-carboxyethyl)-5(and-6) carboxyfluorescein. 7. Using patch-clamp techniques, a high density of pH- and Ca2+-sensitive K+ channels was observed at the apical membrane of MD cells. 8. Other studies found that, at the normal physiological conditions prevailing at the end of the TAL (luminal [NaCl] of 20–60 mmol/L), reabsorption mediated by MD cells is very sensitive to changes in luminal [NaCl].  相似文献   
72.
Summary It is generally agreed that combined deficiency of selenium and vitamin E leads to several abnormalities including Kashin-Beck disease which is an endemic and chronic degenerative osteoarthrosis. The abnormalities can be reversed by the administration of various forms of selenium and vitamin E.The present study was designed to investigate the effects of dietary selenium and vitamin E on bone tissue and on the biomechanical properties of bone. Young rabbits of both sexes were fed with either a selenium- and vitamin E-adequate diet (control group), or a selenium- and vitamin E-deficient diet or a selenium-excess diet. The selenium-deficient diet resulted in a significant decrease in plasma selenium level and the selenium-excess diet resulted in a significant increase in the plasma selenium level with respect to the corresponding control values (p<0.05). The diets did not affect the blood cell counts considerably but erythrocyte glutathione peroxidase activity increased (decreased) relatively when the plasma selenium level increased (decreased) (p<0.05). The light microscopic investigations of the bone tissues of the two experimental groups indicate that the findings of the present work are compatible with osteomalacia. The biomechanical properties of the bones from the three groups were determined experimentally with bending tests. Both the Se-and vitamin E-deficient diet and the Se-excess diet decreased the biomechanical strength of the bones significantly while the bones belonging to the control group always had the largest modulus of elasticity (p<0.05).  相似文献   
73.
In this study, the anti-tumour activity of selenium-protein polysaccharide (SPP), a water extract of the rich selenium Agaricus blazei, was tested both in vivo and in vitro. The results of in vivo experiments show that SPP at doses of 50 and 100 mg/kg inhibits proliferation of implanted Sarcoma 180 by 22 and 37.69%, respectively, and promotes lymphocyte transformation and natural killer (NK) cells activity in tumour bearing mice. During the in vitro experiment, we treated the tumour and non-tumour bearing mice with SPP, and prepared serum treated with SPP (SerumSPP). The results show that SerumSPP, whether from tumour or non-tumour bearing mice, significantly inhibits K562 cells proliferation and induces their apoptosis, and also significantly increases caspase-3 activity of K562 cells. However, the difference in anti-tumour activity of SerumSPP between tumour and non-tumour bearing mice is significantly different (p<0.01). The results, according to the studies both in vivo and in vitro, imply that SPP extracted from rich selenium A. blazei can inhibit growth of implanted Sarcoma 180 and promote lymphocyte transformation and NK cells activity in vivo. Additionally, SerumSPP can inhibit proliferation and cause apoptotic morphological changes and the fragmentation of internucleosomal DNA, and increase caspase-3 activity of K562 cells in vitro, which indicates that apoptosis of K562 cells induced by SerumSPP may be related to up-regulation of caspase-3.  相似文献   
74.
It was recently shown that streptokinase may induce clot formation in vivo by immunoglobulin G mediated platelet stimulation. We evaluated the in vitro effect of streptokinase on platelet function in 103 subjects, of whom 52 were < or = 30 years and 51 were > or = 50 years old. Although streptokinase inhibited platelet aggregation in the majority of cases, in nine the threshold concentration of ADP required to induce irreversible aggregation decreased with streptokinase (1 million Units. l-1) by 30% or more. This observation was confirmed in five of the nine by repeated measurements indicating reproducible streptokinase-induced platelet stimulation. Among the five, two were < or = 30, and three were > or = 50 years old. In none of the five subjects did the radio allergo sorbent test detect type E immunoglobulins directed against streptokinase in the serum. In contrast, in four of the five subjects, streptokinase-induced platelet hyperaggregability was suppressed by addition of goat antibodies against human immunoglobulin G, or F(ab')2-fragments of such antibodies. Acetylsalicylic acid did not prevent streptokinase-induced platelet stimulation, but in three of five cases, led to an increase in the control threshold concentration for ADP, so that after the decrease induced by streptokinase the threshold concentration for ADP was in the same range as before acetylsalicylic acid and streptokinase administration. Thus, streptokinase led to an inhibition of platelet aggregation in the majority of subjects evaluated. In a minority of five out of 103, however, streptokinase reproducibly caused platelet stimulation, presumably mediated by immunoglobulin G.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
75.
用K.S熵(一种信息熵)判别林业系统中生态和经济的协调关系,并提出了控制和改进现有林业系统的有效途径。  相似文献   
76.
维生素E对烧伤小鼠免疫功能改善及其机制   总被引:7,自引:0,他引:7  
张强  李通 《营养学报》1994,16(1):34-38
本实验研究了维生素E(VE)改善烧伤后免疫功能的作用,并对其作用机制进行了探讨。结果显示,小鼠11%~12%总体表面积(TBSA)全层皮肤烧伤后血、肝、脾中过氧化脂质(LPO)水平升高、谷胱甘肽(GSH)含量下降,淋巴细胞增殖反应、白介素一2(IL一2)生成、空斑形成细胞(IJFC)形成及迟发型超敏反应(DTH)均处于抑制状态。投予VE后可防止烧伤动物体内LPO水平、GSH含量明显变化,免疫功能受抑制的程度也明显小于未投予组。以超氧化物歧化酶(SOD)处理的作用与VE相同。体外实验显示,过氧化亚油酸可抑制淋巴细胞增殖反应以及IL一2产生、诱发淋巴细胞脂质过氧化、降低淋巴细胞内GSH含量。淋巴细胞上述功能的抑制与LPO水平密切相关;加入VE可抑制过氧化亚油酸对淋巴细胞的上述作用。提示VE可改善烧伤后免疫功能,其机制可能是通过抗氧化作用而发挥的。  相似文献   
77.
目的探讨广东地区宫颈癌组织中HPV16肿瘤相关性抗原E7基因序列的多态性.方法采用通用引物PCR直接测序法对宫颈癌标本中的HPV分型,从含有HPV16型的标本中采用自行设计的多重引物通过巢式PCR扩增出HPV16E7,经DNA序列测定法检测其基因变异,进而寻找其热点突变.结果50例宫颈癌组织HPV-DNA的检出率为78%,其中HPV16和HPV18型混合感染18例,单纯HPV16型感染15例.33例含有HPV16型的标本中扩增出25例HPV16E7,其中17例647位核苷酸“T”变异“C”,导致相应的蛋白质由天冬氨酸变异为丝氨酸.结论广东地区宫颈癌组织中HPV16E7DNA序列发生碱基替换的区域主要在647位至846位,热点突变点为Nt647和Nt846.  相似文献   
78.
Zusammenfassung 30 Patienten mit klinisch diagnostizierter Alzheimer-Demenz (AD) und 55 etwa gleichaltrige Kontrollprobanden wurden über einen 2-Jahres-Zeitraum prospektiv klinisch, neuroradiologisch und elektroenzephalographisch untersucht, um die longitudinalen Ver?nderungen auf diesen Untersuchungsebenen und ihre Zusammenh?nge zu studieren. In der Kontrollgruppe waren im Beobachtungszeitraum keine wesentlichen Ver?nderungen auf einer der Untersuchungsebenen zu verzeichnen. Bereits inital bestanden signifikante Unterschiede zwischen Patienten und Kontrollen hinsichtlich der kognitiven Leistung, der Ventrikelweite und der absoluten Theta- und Delta-Power. Innerhalb der Patientengruppe verschlechterten sich w?hrend des zweij?hrigen Beobachtungszeitraums die Werte der Blessed-Demenzskala um 7 ± 7 Punkte und im Mini-Mental-State Test um 8 ± 4 Punkte. Die Volumina der Seitenventrikel weiteten sich um mehr als 30 % des Ausgangswertes und die absolute Delta- oder Theta-Power stieg um mehr als 10 % des Ausgangswertes an. Hierdurch nahmen die Unterschiede zwischen Kontroll- und Patientengruppe nochmals zu. Wir konnten keine Zusammenh?nge zwischen Krankheitsbeginn, Alter, Apolipoprotein E4 Gendosis und Krankheitsverlauf belegen. Ein initial schlechter Wert der Patienten auf der Blessed-Skala war mit st?rkeren morphologischen und EEG-Ver?nderungen im Verlauf korreliert, w?hrend initial hohe Theta-Power eine st?rkere funktionelle und kognitive Verschlechterung innerhalb der Patientengruppe pr?dizierte.   相似文献   
79.
The neurochemistry of Alzheimer's disease   总被引:1,自引:0,他引:1  
Our knowledge of the neurochemical pathology of AD has increased immensely the last years. Although it is now clear that mutations in the APP gene can cause some rare hereditary forms of AD, and that ApoE4 is a prominent risk factor for AD, we at present know little about the underlying cause of AD in the general population and the biochemical mechanisms by which the apolipoprotein E4 isoform affects AD pathogenesis. It is hoped that the near future will see a resolution of the current controversies in AD research, including: 1) whether APP mutations cause Alzheimer's disease by affecting Aβ deposition or the function of APP itself; 2) whether abnormal phosphorylation of tau is a central pathogenetic event, or whether it occurs as epiphenomena that reflect general neurodegeneration in a variety of disease processes; 3) Whether Aβ deposition in the brain is the central event in AD or whether it occurs as epiphenomena in a variety of brain disorders such as head trauma; and 4) whether altered tau phosphorylation occurs secondary to Aβ deposition or vice versa, and what the link is (if any) between the two processes.  相似文献   
80.
蘑菇多糖对小鼠腹腔巨噬细胞作用的体外研究   总被引:5,自引:0,他引:5  
目的 观察蘑菇多糖对小鼠腹腔巨噬细胞免疫调节作用及对体外培养的肿瘤细胞作用的影响。方法 采用比色法测定经蘑菇多糖处理的巨噬细胞内LDH的活性。MTT法观察蘑菇多糖与巨噬细胞的共同培养上清对HL-60细胞及K562细胞的抑制率。结果 (1)蘑菇多糖明显激活小鼠腹腔巨噬细胞的共同培养上清对HL-60细胞及K562细胞的抑制率。结果 (1)蘑菇多糖明显激活小鼠腹腔巨噬细胞,显著提高巨噬细胞的LDH活性;(2)蘑菇多糖作用下的巨噬细胞上清液可显著抑制HL-60细胞及K562细胞的增殖。结论 蘑菇多糖的抗肿瘤作用可能是通过激活小鼠腹腔巨噬细胞的活性实现的。  相似文献   
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