Mesenchymal stem cells (MSCs) are potential sources of cells for tissue repair. However, little information is available about the time course of homing and differentiation of systemically delivered MSCs after acute myocardial ischemia (MI). In the present study, MSCs were isolated from male rat bone marrow and expanded in vitro. Female rats were divided randomly into three groups. Three hours after coronary ligation, the transplanted group received an infusion of MSCs through the tail vein; at the same time, a coronary-ligated control group was injected with culture medium, and a normal (unligated) group received MSCs. Homing of MSCs to the heart was assessed by expression of the Y chromosome sry gene using fluorescence in situ hybridization (FISH) at 3 days, 1, 4, and 8 weeks after transplantation. Immunofluorescent staining was used to examine markers for cardiomyocytes, endothelial cells, and smooth muscle cells. Hemodynamics in the hearts was also measured to assess cardiac function. At each time point, sry-positive cells were present in the cardiac tissue in transplanted group but not in the hearts of normal and control group animals. The number of sry-positive cells was significantly higher at 1 week compared to 3 days after transplantation. No significant difference was found in the number of sry-positive cells among those of 1, 4, and 8 weeks after transplantation. At 3 days and 1 week after transplantation, the sry-positive cells in the transplanted group lacked troponin, desmin, smooth muscle alpha-actin, and CD31. At the later time points, cardiomyocytes, smooth muscle cells, and endothelial cells bearing sry were identified in the transplanted group. The cardiac function in transplanted group showed higher improvement at 4 and 8 weeks compared to 1 week after transplantation. Our data suggest that intravenously delivered MSCs are capable of homing toward the ischemic myocardium, and the fastigium of homing appeared around 1 week after MI. The differentiation of MSCs to cardiomyocytes, smooth muscle cells, and endothelial cells shows to be time dependent and arises at 1 to 4 weeks after transplantation.
This paper presents our experiments and analysis of the electrical tree growing characteristics. The relationship between electrical tree propagation and the material morphology in XLPE cable insulation has been studied by researching the structure and growth characteristics of a double structure electrical tree. It has been found that, due to the influence of uneven congregating state, difference in crystalline structure, and the existence of residual stress in semi-crystalline polymer, five types of electrical tree structures (branch, bush, bine-branch, pine-branch, and mixed configurations) would propagate in XLPE cable insulation. Three basic treeing propagation phases (initiation, stagnation, and rapid propagating phases) are presented in electrical tree propagating process. If initiation phase is very active, the single branch tree will propagate while if this phase is weak then the bush tree will occur more easily. There would be a clear double structure of electrical tree when it grows at submicroscopic structure uneven region of the material. A new parameter, the expansion coefficient is introduced to describe the electrical tree propagation characteristics. In addition, two other coefficients being used to describe our experimental results are dynamic fractal dimension and growth rate of electrical tree.
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