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Photochemically induced increase in endothelial permeablity regulated by RhoA activation
Ota, Hiroki,Matsumura, Mimiko,Miki, Norihisa,Minamitami, Haruyuki Korean Society of Photoscience 2009 Photochemical & photobiological sciences Vol.8 No.10
Photochemical reactions used in photodynamic therapy are reported to damage normal cells and tissues in ways that increase endothelial permeability and thereby cause excessive neointimal formation and subsequent restenosis. To investigate the mechanisms of this permeability increase in vitro, human umbilical vein endothelial cells were incubated with the porphyrin precursor $\delta$-aminolevulinic acid and then irradiated with a 646 nm light-emitting diode (LED). Results using Transwells${(R)}$ supports showe that the photochemical reaction increased endothelial permeability by 200%, and fluorescence microscopy revealed that destruction of the capillary-like structures due to cell shrinkage was accompanied by VE-cadherin mislocalization and stress fiber formation. The generated gaps between cells were observed using dyed ${\beta}1$-integrin and total internal reflection fluorescence microscopy. Western blotting indicated that the photochemical reaction phosphorylated GDP-RhoA to GTP-RhoA, a protein that promotes stress fiber formation and inhibits VE-cadherin production.When forskolin/rolipram or 8CPT-2'O-Me-cAMP, both of which inhibit further reaction of phosphorylated RhoA, were added, no formation of stress fibers or mislocalization of VE-cadherin was observed, thus preventing an increase in endothelial permeability. Taken together, photochemically induced RhoA activation appears to play a key role in increasing endothelial permeability during changes in morphology of endothelial cells.
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Study of Workpiece Vibration in Powder-Suspended Dielectric Fluid in Micro-EDM Processes
Gunawan Setia Prihandana,Muslim Mahardika,Mohd Hamdi,Yoke San Wong,Norihisa Miki,Kimiyuki Mitsui 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.
Abstract. In micro-EDM (electrical discharge machining), improper removal of debris causes short-circuiting between a tool electrode and a workpiece and in turn, prevents continuous machining process. Therefore, a remarkably longer period of time is required to fabricate a through hole than that would be required when no short-circuiting took place. In order to solve this problem, the dielectric fluid is immersed with graphite nano powders to reduce machining time and improve surface quality due to the less frequent of arcing between the tool electrode and the workpiece. However, excess powders become debris and subsequently deteriorate the efficiency of machining. To fully exploit the effects of the suspended powders, we introduced vibration of the workpiece in order to remove the debris in the small gap between the workpiece and electrode efficiently. The experimental results showed that combination of these techniques improved machining stability, assured continuous machining processes, and significant reduction of the machining time. Reduction of the machining time and the surface roughness of the workpiece after machining were investigated with respect to the powder concentrations when the workpiece was vibrated at 1000 Hz.
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