Wave-front curvature as a cause of slow conduction and block in isolated cardiac muscle

We have investigated the role of wave-front curvature on propagation by following the wave front that was diffracted through a narrow isthmus created in a two-dimensional ionic model (Luo-Rudy) of ventricular muscle and in a thin (0.5-mm) sheet of sheep ventricular epicardial muscle. The electrical activity in the experimental preparations was imaged by using a high-resolution video camera that monitored the changes in fluorescence of the potentiometric dye di-4-ANEPPS on the surface of the tissue. Isthmuses were created both parallel and perpendicular to the fiber orientation. In both numerical and biological experiments, when a planar wave front reached the isthmus, it was diffracted to an elliptical wave front whose pronounced curvature was very similar to that of a wave front initiated by point stimulation. In addition, the velocity of propagation was reduced in relation to that of the original planar wave. Furthermore, as shown by the numerical results, wave-front curvature changed as a function of the distance from the isthmus. Such changes in local curvature were accompanied by corresponding changes in velocity of propagation. In the model, the critical isthmus width was 200 microns for longitudinal propagation and 600 microns for transverse propagation of a single planar wave initiated proximal to the isthmus. In the experiments, propagation depended on the width of the isthmus for a fixed stimulation frequency. Propagation through an isthmus of fixed width was rate dependent both along and across fibers. Thus, the critical isthmus width for propagation was estimated in both directions for different frequencies of stimulation. In the longitudinal direction, for cycle lengths between 200 and 500 milliseconds, the critical width was < 1 mm; for 150 milliseconds, it was estimated to be between 1.3 and 2 mm; and for the maximum frequency of stimulation (117 +/- 15 milliseconds), it was > 2.5 mm. In the transverse direction, critical width was between 1.78 and 2.32 mm for a basic cycle length of 200 milliseconds. It increased to values between 2.46 and 3.53 mm for a basic cycle length of 150 milliseconds. The overall results demonstrate that the curvature of the wave front plays an important role in propagation in two-dimensional cardiac muscle and that changes in curvature may cause slow conduction or block.     

Preweaning growth traits for Senepol, Hereford, and reciprocal crossbred calves and feedlot performance and carcass characteristics of steers

We conducted a multiyear study in two phases to determine preweaning performance traits of Senepol (S x S), Hereford (H x H), and reciprocal (S x H and H x S) F1 crossbred calves and feedlot performance and carcass characteristics of steers. In Phase I, from 1985 to 1989, data from S x S (n = 194), H x H (n = 383), and S x H (n = 120) calves were used. Numbers of S x S cows were increased during Phase I so that data from H x S (n = 74) calves could be included in Phase II (1990 to 1992) in addition to S x S (n = 118), H x H (n = 130), and S x H (n = 56) calves. Also during Phase II, feedlot performance and carcass characteristics were determined for S x S (n = 30), H x H (n = 26), H x S (n = 36), and S x H (n = 26) steers. In Phase I, S x S calves had heavier (P < .01) birth weights and heavier (P < .01) 205-d adjusted weaning weights than H x H calves. Birth weights of S x H calves were heavier (P < .01) than the mean of the purebred calves, but 205-d adjusted weaning weights did not differ (P > .10). In phase II, direct heterosis was 3.5% for birth weight (P < .05) and 5.1% for 205-d adjusted weaning weight (P < .01). Senepol maternal breed effects were 1.9 kg for birth weight (P < .10) and 37.9 kg for 205-d adjusted weaning weight (P < .01). Levels of direct heterosis, Senepol maternal breed effects, and Hereford direct breed effects were significant for most feedlot performance traits of steer calves that were fed to a common end point. Breeds did not differ (P > .10) for USDA yield and quality grades, and direct heterosis was not significant for Warner-Bratzler shear force. These results demonstrate significant levels of heterosis in preweaning performance between S x S and H x H calves and in feedlot performance of steers. Levels of heterosis were smaller and nonsignificant for most carcass traits including meat tenderness, which did not differ between S x S and H x H steers in this study.     

Evidence that the RdeA protein is a component of a multistep phosphorelay modulating rate of development in Dictyostelium

We have isolated an insertional mutant of Dictyostelium discoideum that aggregated rapidly and formed spores and stalk cells within 14 h of development instead of the normal 24 h. We have shown by parasexual genetics that the insertion is in the rdeA locus and have cloned the gene. It encodes a predicted 28 kDa protein (RdeA) that is enriched in charged residues and is very hydrophilic. Constructs with the DNA for the c-Myc epitope or for the green fluorescent protein indicate that RdeA is not compartmentalized. RdeA displays homology around a histidine residue at amino acid 65 with members of the H2 module family of phosphotransferases that participate in multistep phosphoryl relays. Replacement of this histidine rendered the protein inactive. The mutant is complemented by transformation with the Ypd1 gene of Saccharomyces cerevisiae, itself an H2 module protein. We propose that RdeA is part of a multistep phosphorelay system that modulates the rate of development.     

硫脲浸出液活性炭负载洗脱研究

从硫脲浸出液中活性炭负载洗脱金是比较困难的,目前在这方面发表的文献并不很多。本文着重研究并讨论了从负载活性炭上洗脱金的不同方法,包括酸性硫脲有机溶液和非有机洗脱液。研究了丙酮、乙腈、丁醇、乙二醚和乙醇5种有机溶剂。研究了不同的硫脲、硫酸和有机溶剂的浓度和温度对洗脱的影响。试验表明了这5种有机溶剂对金的洗脱能力按如下顺序排列: 丁醇>乙腈>乙二醚>乙醇>丙酮当采用5%丁醇,50～100g/L硫脲和50～100g/L硫酸,温度40～60℃时,金的洗脱率可达98～99%,此时活性炭含金降至0.10mg/g以下。对于非有机洗脱液,像硫化钠和硫代硫酸钠,研究表明金的洗脱率主要取决于溶液的浓度和温度,在室温时,1～2mol的硫化钠溶液可以洗脱99%的金。如果溶液的浓度降低至0.5mol,则温度需升至80℃以上才可能获得相同的洗脱率。     

取代苯甲酸葡萄糖酯的合成及生物活性

以两种方法合成了10个取代苯甲酸葡萄糖酯类化合物，一是相转移催化法，二是在三忆胺的存在下，取代苯甲酸与溴代葡萄糖反应，该种合成糖酯的方法未见文献报道，取代苯甲酸葡萄糖酯的结构由IR、MS、^1H NMR和元素分析确认。对化合物的抗病毒活性测试结果发现，其中有两个化合物具有一定的抑制TMV的活性。     

Heartworm infected dogs in the Netherlands

Heartworm infected small animal patients are seldom seen in the Netherlands, because the parasite's life cycle cannot be completed in this climate. We report here four cases of the disease in dogs brought to the Netherlands from endemic heartworm areas. The initial diagnosis was based upon this knowledge and clinical signs (low exercise tolerance and coughing). The diagnosis was confirmed by the radiographic finding of variable pulmonary artery enlargement, the electrocardiographic finding of right ventricular hyperptrophy and the presence of microfilariae in the peripheral blood. Treatment resulted in recovery in three of these patients but the fourth died soon after initiation of the therapy.