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991.
The present study examines the similarity in the symptoms and binding properties between the depressant and excitatory insect-selective neurotoxins, derived from scorpion venom. A comparison of their primary structures and neuromuscular effects is presented. A new depressant toxin (LqhIT2) was purified from the venom of the scorpion Leiurus quinquestriatus hebraeus. The effects of this toxin on a prepupal housefly neuromuscular preparation mimic its effects on the intact insect, i.e, a brief period of repetitive bursts of regular junction potentials (JPs) is followed by reduced amplitude JPs ending with a block of the neuromuscular transmission. "Loose" patch clamp recordings indicate that the repetitive activity has a presynaptic origin (the motor nerve) and resembles the effect of the excitatory toxin AaIT. The final synaptic block is supposed to be the end result of neuronal membrane depolarization. Such an effect is not caused by an excitatory toxin, which induces long "trains" of repetitive firing. The amino acid sequences of three depressant toxins were determined by automatic Edman degradation indicating a high degree of sequence homology. This conservation differs from those of other groups of scorpion toxins. The opposing pharmacological effects of depressant toxins are discussed in light of the above neuromuscular effects and sequence analysis. A genetic approach in the study of the structure-function relationships of the depressant toxins was initiated by isolating cDNA clones encoding the LqhIT2 and BjIT2 toxins. Their sequence analysis revealed the precursor form of these toxins: A 21 amino acid residue signal peptide followed by a 61 amino acid region of the mature toxin, and three additional amino acids at the carboxy terminus. 相似文献
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993.
采用热分析、X射线衍射、扫描电镜等方法对Mo-La2O3阴极中La2O3与Mo2C的反应情况进行了研究.实验结果表明:La2O3与Mo2C在高温下可以发生化学反应,产生单质La和金属Mo;反应物存在状态不同,二者发生反应的温度不同. 粉末样品中二者反应温度(1203K)低于阴极丝中二者的反应温度(1533K). 相似文献
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997.
Two scaled formats for summarizing the results of psychosocial evaluations of transplant candidates have been published, the Psychosocial Assessment of Candidates for Transplantation (PACT) and the Transplant Evaluation Rating Scale (TERS). In this study, 40 consecutive candidates for bone marrow transplant were rated on the PACT and TERS. The PACT and TERS were comparable in interrater reliability. Similar conceptual items for each scale correlated fairly highly with one another. The PACT and TERS differ in several scale characteristics. The authors discuss the relationship between scale characteristics and clinical utility. 相似文献
998.
The extent of interdialytic weight gain (IDWG) in chronic hemodialysis patients is usually attributed to the level of compliance with fluid restriction. However, in view of the substantial water content of food (and caloric content of beverages), IDWG also may be a function of calorie and protein intake and may reflect the nutritional state of patients. To investigate this theory, the relationship between 2-day IDWG and body weight, normalized protein catabolic rate (nPCR), serum albumin, and delivered Kt/V urea was assessed in a prospective, randomized study of 860 chronic hemodialysis patients in 56 dialysis units. Compared with patients having < 2 kg IDWG (n = 378), patients with > 3 kg IDWG (n = 138) weighed more (dry weight, 76.8 v 61.7 kg), had higher nPCR (1.15 v 0.96 g/kg/d), and had higher serum albumin levels (3.96 vs 3.79 g/dL) (all P < 0.001) but did not have different levels of Kt/V (1.04 v 1.06). When IDWG was assessed as a function of dry weight, patients with IDWG > 4.5% of dry weight (n = 151) had higher nPCR (1.17 v 0.94 g/kg/d) but weighed less (60.1 v 70.0 kg) and had a higher Kt/V (1.14 v 1.01) than patients with IDWG < 3% of dry weight (n = 355) (all P < 0.001). Artifactual association between IDWG and nPCR attributable to an accentuated two-pool effect from differing ultrafiltration requirements was unlikely as assessed by the relationship between modeled Kt/V and prescribed Kt/V determined using an anthropometric urea volume.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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