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S25.2. Mechanical stability of a biconcave red blood cell requires a nonuniform membrane structure
194
Symposia
Vol. 32, Nos. 2-3
xenogeneic cell implants by membranes that provide a physical means for preventing host cellular and molecular interactions that could lead to implant rejection, instead of pharmacological means to address the immunological aspects of rejection. Finally, tissue-engineered products, as manufactured equivalents of functional body parts that include living components, can use physical mechanisms in the process of fabrication to separate, isolate, organize, or transport the living component for therapeutic applications. $25.2. MECHANICAL STABILITY OF A BICONCAVE RED BLOOD CEI.IJ R E Q U I R E S A NONUNIFORM MEMBRANE STRUCTURE R. S. CHADWICK Biomechanics Group, Biomedical Engineering and Instrumentation Program, National Center for Research Resources, National Institutes of Health, Bethesda, MD 20892, USA Macroscopic membrane theory with bending assumed to be small compared to in plane membrane tractions is used to show that the biconcave shape of the red blood cell is not mechanica.lly stable unless the membrane is locally subjected to a purely radial force directed away from the axis of revolution. Here it is proposed that this force has an internal molecular origin with a tangential component stemming from lateral structural nonuniformity and a normal component arising from structural asymmetry of the bilayer leaflets. The membrane locally orients itself so that the resultant of these components is in the radial direction. A model for these forces based on the concept of osmotic pressure in a two dimensional solution, together with the stability condition, predicts that the concentration of an immobilized molecular constituent must increase from the dimple region toward the rim. $25.3. IN VITRO CD62E AND CD54 RELATED ADHESION NEUTROPHIIS TO ENDOTHELIAL CELLS: INFLUENCE BUFLOMEDIL
OF OF
M. R. BOISSEAU, M. SEIGNEUR, C. CLOSSE, A. PRUVOST University de Bordeaux II, 33076 Bordeaux, France The adhesion of leukocytes to endothelium has been recently investigated in in vivo models of the microcirculation and in vitro, using cultivated endothelium, leading to a precise knowledge of the involved immuno-biochemical mechanisms. Here is presented a technique based upon the stable adhesion: umbilical vein endothelial cell cultures (HUVEC) at confluence are submitted 4 hours to ILl (10 UI/ml), inducing the synthesis and membrane expression of E-selectin (CD62E) and ICAM-1 (CD54). Isolated human neutrophils are coincubated 20 min. at 37 ° C, then rinsed to remove non adherent leukocytes. Trypsin treatment (0.05%) allows the detachment of both endothelial cells and neutrophils. The 2 populations of cells are subsequently stained by DIO C6 and the quantitative discrimination is performed by flow cytometry analysis (ODAM Brucker 3000). Pharmacology: in this model buflomedil decreased the neutrophil adherence, either after incubation with the white cells (significant at
Symposia
Vol. 32, Nos. 2-3
xenogeneic cell implants by membranes that provide a physical means for preventing host cellular and molecular interactions that could lead to implant rejection, instead of pharmacological means to address the immunological aspects of rejection. Finally, tissue-engineered products, as manufactured equivalents of functional body parts that include living components, can use physical mechanisms in the process of fabrication to separate, isolate, organize, or transport the living component for therapeutic applications. $25.2. MECHANICAL STABILITY OF A BICONCAVE RED BLOOD CEI.IJ R E Q U I R E S A NONUNIFORM MEMBRANE STRUCTURE R. S. CHADWICK Biomechanics Group, Biomedical Engineering and Instrumentation Program, National Center for Research Resources, National Institutes of Health, Bethesda, MD 20892, USA Macroscopic membrane theory with bending assumed to be small compared to in plane membrane tractions is used to show that the biconcave shape of the red blood cell is not mechanica.lly stable unless the membrane is locally subjected to a purely radial force directed away from the axis of revolution. Here it is proposed that this force has an internal molecular origin with a tangential component stemming from lateral structural nonuniformity and a normal component arising from structural asymmetry of the bilayer leaflets. The membrane locally orients itself so that the resultant of these components is in the radial direction. A model for these forces based on the concept of osmotic pressure in a two dimensional solution, together with the stability condition, predicts that the concentration of an immobilized molecular constituent must increase from the dimple region toward the rim. $25.3. IN VITRO CD62E AND CD54 RELATED ADHESION NEUTROPHIIS TO ENDOTHELIAL CELLS: INFLUENCE BUFLOMEDIL
OF OF
M. R. BOISSEAU, M. SEIGNEUR, C. CLOSSE, A. PRUVOST University de Bordeaux II, 33076 Bordeaux, France The adhesion of leukocytes to endothelium has been recently investigated in in vivo models of the microcirculation and in vitro, using cultivated endothelium, leading to a precise knowledge of the involved immuno-biochemical mechanisms. Here is presented a technique based upon the stable adhesion: umbilical vein endothelial cell cultures (HUVEC) at confluence are submitted 4 hours to ILl (10 UI/ml), inducing the synthesis and membrane expression of E-selectin (CD62E) and ICAM-1 (CD54). Isolated human neutrophils are coincubated 20 min. at 37 ° C, then rinsed to remove non adherent leukocytes. Trypsin treatment (0.05%) allows the detachment of both endothelial cells and neutrophils. The 2 populations of cells are subsequently stained by DIO C6 and the quantitative discrimination is performed by flow cytometry analysis (ODAM Brucker 3000). Pharmacology: in this model buflomedil decreased the neutrophil adherence, either after incubation with the white cells (significant at