Biomedical subjects

S Q Liu

Publications and source records attributed to S Q Liu.

At least 73 records · Page 4Linked to original sources

PubMed1993

Cell growth on immobilized cell growth factor. 6. Enhancement of fibroblast cell growth by immobilized insulin and/or fibronectin.

A cell growth factor protein (insulin) and/or a cell-adhesion protein (fibronectin) were immobilized on surface-hydrolyzed poly(methyl methacrylate) membranes. The growth of mouse fibroblast cells STO was accelerated by the immobilized insulin. This acceleration was enhanced by introduction of spacer arms. Coimmobilization of insulin and fibronectin was very effective for the acceleration of cell growth.

Adsorption↗

PubMed1993

Cell growth on immobilized cell growth factor. 9. Covalent immobilization of insulin, transferrin, and collagen to enhance growth of bovine endothelial cells.

Bovine endothelial cells were cultivated on the surface of polyurethane membranes or tubes immobilized with insulin, transferrin, and/or collagen, and growth was measured. For the purpose of immobilization, amino groups were introduced on the membranes or tubes by glow-discharge treatment in the presence of ammonia gas. The proteins were coupled to the amino groups on the surfaces by using dimethyl suberimidate (DMS) or water-soluble carbodiimide (WSC). Growth of bovine endothelial cells was higher on immobilized insulin or transferrin using DMS than that using WSC. The cell growth was higher on immobilized insulin or transferrin than on free insulin or transferrin, respectively. Though immobilized collagen did not affect the cell growth, coimmobilization with insulin or transferrin brought about greater acceleration of cell growth. In addition, the immobilized collagen was indispensible to maintain the endothelial cells on the material surface for a long time. The endothelial cells grown in the polyurethane tubes, on which insulin and collagen are coimmobilized, kept a normal cobblestone-like appearance and maintained the ability to secrete prostacyclin for 9 months.

Adsorption↗

PubMed1993

Material coefficients of the strain energy function of pulmonary arteries in normal and cigarette smoke-exposed rats.

The effect of cigarette smoke on the stress-strain relationship of pulmonary arteries was studied in 2- and 3-month smoke-exposed rats. The animals were exposed to cigarette smoke in a smoke-generating system 10 times daily with one cigarette each time. The smoke density and the puffing duration and frequency of the system were regulated in accordance with reference values measured from human smokers. The mechanical properties of the pulmonary arteries about 450 microns in external diameter (at zero pressure) were determined in vitro by inflation and deflation tests. The average stress and middle-wall strain of the selected pulmonary arteries were determined on the basis of experimental data including inflation and deflation pressures during loading and unloading processes, respectively, and vessel diameter and length at various pressure levels, and vessel circumferential and longitudinal lengths at zero-stress state. A constitutive equation for the pulmonary arteries was derived from an energy function depending on circumferential and longitudinal Green's strains. The coefficients of the strain energy function of the pulmonary arteries were determined in both the smoke-exposed and control rats by fitting the experimental stress-strain data with the constitutive equation. It was found that the wall stress of the pulmonary arteries at a given strain and most of the coefficients of the strain energy function were increased in both the 2- and 3-month smoke-exposed rats in comparison with those in the corresponding controls. These results indicated that cigarette smoke induced an increase in the wall stiffness of the pulmonary arteries in the rats.

Animals↗

PubMed1993

Cell growth on immobilized cell growth factor. 7. Protein-free cell culture by using growth-factor-immobilized polymer membrane.

A protein-free culture of anchorage-dependent cells, mouse fibroblast cells, STO and 3T3-L1 and fibroic sarcoma cells, Swiss albino HSDM1C1, grown on a cell-growth protein, insulin, and/or a cell-adhesion protein, collagen, which are immobilized or coimmobilized on surface-hydrolyzed poly(methyl methacrylate) membrane, was investigated. By adding metal ions and lipids to the culture medium, a protein-free culture medium was composed, which was potent in promoting cell proliferation similarly to serum-containing culture medium. In particular, with insulin/collagen-coimmobilized membrane, a protein-free culture was established without detachment of growing cells over a long period. These protein-immobilized membranes could be used repeatedly.

Amino Acid Sequence↗

PubMed1993

Cell growth on immobilized cell growth factor: 5. Interaction of immobilized transferrin with fibroblast cells.

Transferrin was immobilized on poly(methyl methacrylate) membrane and the interaction of the immobilized transferrin with mouse fibroblast cells STO was investigated. The immobilized transferrin was stable without decomposition over 48 h and showed higher activities of cell growth acceleration than free transferrin and transported ferric ion as effectively as free transferrin. The specific interaction of the immobilized transferrin with fibroblast cells was confirmed by experiment using the antibody. It was considered that cell growth acceleration and ferric ion transportation occur by different mechanisms.

Animals↗

PubMed1993

Study of blood compatible polymers. III. Copolymers of N-benzyl, N-(2-hydroxyethyl) acrylamide and 2-hydroxyethyl methacrylate.

Copolymerization of 2-hydroxyethyl methacrylate (HEMA) and N-benzyl, N-(2-hydroxyethyl) acrylamide (BENAAm) was carried out at different mole ratios of the monomers to obtain copolymers of varying composition. BENAAm content of the copolymers varies between 13 and 70%. Investigation of the interaction of rabbit platelets with these polymer surfaces showed that copolymers with higher BENAAm content inhibit the platelet deformation. Human umbilical cord fibroblast cells proliferated very well on the copolymer surfaces. The cell growth rate on polyHEMA was relatively low. Maximum cell growth was observed on the copolymer having 87% HEMA.

Acrylic Resins↗

PubMed1993

Elementary mechanics of the endothelium of blood vessels.

The endothelium lining human arteries is a continuum of endothelial cells. The flowing blood imposes a shear stress on the endothelium. To compute the internal stress in the endothelium, we use two alternative hypotheses: 1) The cell content is fluid-like so that at steady-state it has no shear stress. 2) The cell content is solid-like. Under hypothesis No. 1, the membrane tension in the upper cell membrane grows in the direction opposite to the blood flow at a rate equal to the blood shear stress. At the junction of two neighboring cells the membrane tension in the downstream cell is transmitted partly to the basal lamina, and partly to the upstream cell. The transmission depends on the osmotic or static pressure difference between the cell and blood. If the static pressure difference is zero, the tension in the upper cell membrane will accumulate upstream. At other values of static pressure, the cell membrane tension may increase, decrease, or fluctuate along the vessel depending on the inclination of the side walls of the cells at the junctions. To determine the sidewall inclinations, we propose to use the complementary energy theorem. Under hypothesis No. 2, the cell content can bear shear, which tends to reduce the cell membrane tension; but the cell membrane tension accumulation phenomenon discussed above remains valid. These results are used to analyze the interaction of the cell membrane and cell nucleus; and the effect of turbulences in the flow on causing large fluctuations in cell membrane tension and vertical oscillations of the nuclei. The implication of tensile stress on the permeability of the cell membrane is discussed. We conclude that for the study of mass transport and stress fibers in the endothelial cells, one should consider the interaction of neighboring endothelial cells as a continuum, and shift attention from the shear stress in the blood to the principal stresses in the cells.

Animals↗

PubMed1993

Remodeling of the constitutive equation while a blood vessel remodels itself under stress.

Changes in the mechanical properties of a blood vessel when it remodels itself under stress are reviewed. One of the recent findings about blood vessels is the rapidity of tissue remodeling when the blood pressure is changed. When the tissue structure and material composition remodel, the zero-stress state of the vessel changes. The mechanical properties change also in the remodeling process. If the elastic behavior is expressed in terms of a pseudo-elastic strain-energy function, then the constants in the function will change in the course of the remodeling. With all these changes taking place, the scope of constitutive equations broadens: it should now include a mass-and-structure growth-stress relationship as well as a stress-strain-relationship. To obtain the mass-and-structure growth-stress relationship, one must be able to determine the mechanical properties of the different layers of the vessel wall, as well as the chemical composition and morphology. For the blood vessels, new methods of mechanical testing must be introduced. A key thought is to use bending of the blood vessel wall. By bending, different layers of the vessel wall are subjected to different stresses, leading to equations that can be used to solve the inverse problem of determining the stress-strain law from measured stress and strain. In vitro and in vivo experiments and theoretical prospectives are presented.

Adaptation, Physiological↗

PubMed1993

Eosin-5-maleimide inhibits red cell Cl- exchange at a noncompetitive site that senses band 3 conformation.

Eosin-5-maleimide (EM) has been used as a fluorescent probe for the external-facing transport site of the human erythrocyte band 3 protein. Changes in chloride concentration at both sides of the membrane have no significant effect on the inhibitory potency of EM as a reversible inhibitor of Cl- exchange at 0 degrees C, however, demonstrating that it is not a competitive inhibitor. The affinity of EM for the form of band 3 with the transport site facing outward is approximately five times greater than for the form with the transport site facing the cytoplasm; binding of iodide to the external transport site causes no statistically significant decrease in affinity for EM. Eosin, without the maleimide moiety, is a slightly more potent inhibitor than is EM. Erythrosin, an analogue with four iodide atoms replacing the four bromide atoms in eosin, is a much more potent inhibitor, with a half-inhibitory concentration of only 3.1 microM, > 30 times lower than that of EM. Neither eosin nor erythrosin inhibition is affected by changes in chloride concentration as would be expected for a competitive inhibitor. Thus EM and the other eosin derivatives bind to a site separate from the external transport site, but one that is affected by the changes of transport site conformation from the inward-facing to the outward-facing state.

Anion Exchange Protein 1, Erythrocyte↗

PubMed1993

Lys-430, site of irreversible inhibition of band 3 Cl- flux by eosin-5-maleimide, is not at the transport site.

Although eosin-5-maleimide (EM) covalently labels band 3 and has been thought to react at the external-facing anion transport site, EM reversibly inhibits Cl- exchange at 0 degrees C in a noncompetitive fashion, indicating that under these conditions it does not bind to the transport site [Knauf, P.A., N.M. Strong, J. Penikas, R.B. Wheeler, Jr., and S.J. Liu. Am. J. Physiol. 264 (Cell Physiol. 33): C1144-C1154 1993]. To see whether or not the covalent labeling by EM takes place at the same noncompetitive site as the reversible binding, we examined the dependence of reaction rate on EM concentration. The reaction rate saturates with increasing EM concentration, indicating that reversible binding precedes covalent reaction and that EM therefore acts as an affinity label. A more complex model in which reversible binding prevents a bimolecular reaction at a different site cannot, however, be ruled out. Cl- gradients across the membrane affect EM reversible binding in a manner suggesting that EM binds preferentially to the Eo form of band 3, with the transport site unloaded and facing outward. Thus EM binds to and probably reacts covalently with a site that is different from the transport site, but whose conformation is affected by the orientation of the transport site. Lysine-430, the amino acid residue which is covalently labeled by EM (4), may be near the transport site but does not seem to be directly involved in the binding of transported substrates such as chloride. EM binding to one band 3 monomer decreases the reactivity of the adjacent monomer but does not decrease the affinity constant of the reversible binding step that precedes covalent reaction. Although a small fraction (approximately 1%) of band 3 monomers fail to react with EM, EM nearly completely inhibits transport in those monomers with which it reacts.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1993

Changes in the structure and mechanical properties of pulmonary arteries of rats exposed to cigarette smoke.

The effect of cigarette smoke on the structure and mechanical properties of pulmonary arteries was studied in 2- and 3-month smoke-exposed rats. The animals were exposed to cigarette smoke in a smoke-generating system 10 times per day with one cigarette each time. The smoke density and the puffing duration and frequency of the system were regulated in accordance with reference values measured from human smokers. The volume fractions of the cells, including smooth muscle cells and fibroblasts, and extracellular matrix components, including collagen, elastin, and remainder (components not specified in this study), of the pulmonary arteries of approximately 450 microns in external diameter (at zero pressure) were determined in smoke-exposed and control rats by using an electron microscopic method. It was found that the volume fractions of the fibroblasts, the collagenous bundles, and the elastic laminae of the pulmonary arteries were increased significantly, whereas those of the smooth muscle cells and the remainder were decreased significantly in both the 2- and 3-month smoke-exposed rats in comparison with those of the corresponding control rats. The mechanical properties of the pulmonary arteries were determined based on the in vitro dimensional measurement of the vessels at various inflation pressures and zero-stress state. An increase in the stiffness of the pulmonary arteries was found in both the 2- and 3-month smoke-exposed rats. We conclude that cigarette smoke can induce structural and mechanical remodeling in the pulmonary arteries of rats.

Animals↗

PubMed1993

[Immunoelectron-microscopic localization of a 54-kDa protein overexpressed by chloroquine-resistant Plasmodium berghei ANKA strain].

A 54-kDa protein overexpressed by chloroquine-resistant Plasmodium berghei ANKA strain was first reported by us. In this paper, the localization of this protein by immunoelectron microscopy is presented. The results showed that the protein was mainly scattered inside the cytoplasm of the early, late trophozoites and schizonts of erythrocytic stage of P. berghei ANKA strain, and some of it was also found in cytoplasm of erythrocytes infected with parasites. The protein content was much higher in chloroquine-resistant P. berghei ANKA strain than in chloroquine-sensitive P. berghei ANKA strain, suggesting the importance of this protein in understanding mechanism of chloroquine resistance in malaria parasites.

Animals↗

PubMed1993

[A technique for bone marrow biopsy specimen preservation].

The rapidly frozen bone marrow specimen was displaced in iced acetone at low temperature first and was embedded in low-temperature glycol methacrylate resin subsequently which was then ready for cryostat section preparation. Since there was no routine fixation required, so that the morphology features will be well preserved for further immunohistochemical and histochemical studies. By this technique, the enzyme activity and localization site will also be well preserved, particularly the lymphoid cell surface antigens, and it is also valuable for retrospective study of biopsy specimens.

Biopsy↗

PubMed1992

Does sorbinil bind to the substrate binding site of aldose reductase?

With benzyl alcohol as the varied substrate, sorbinil was found to be a competitive inhibitor of aldose reductase, an enzyme implicated in the etiology of secondary diabetic complications. The K(is sorbinil) and the Vmax/Km (V/K) benzyl alcohol decreased at low pH with a pK of 7.5 and 7.7, respectively. These observations suggest that both sorbinil and benzyl alcohol bind to the same site on the enzyme. Active site inhibition by sorbinil is consistent with non-competitive inhibition patterns of sorbinil with nucleotide coenzyme or aldehyde as the varied substrate in the direction of aldehyde reduction.

Aldehyde Reductase↗

PubMed1992

Carboxymethylation-induced activation of bovine lens aldose reductase.

Carboxymethylation of bovine lens aldose reductase with 10 mM iodoacetate for 1 h at 25 degrees C led to a more than 4-fold increase in kcat. Carboxymethylation led to a 3- to 5-fold increase in Km NADPH and Km D-glyceraldehyde, whereas Km L-glyceraldehyde increased approx. 30-fold. Activation of the enzyme on carboxymethylation was accompanied by a decrease in the sensitivity of the enzyme to inhibition by 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), sorbinil (Kii increased from 0.4 to 109 microM) and NADP (Kis increased from 0.01 to 0.03 mM), but not tolrestat. Activation of the enzyme was almost completely prevented by NADPH and to a lesser extent by DL-glyceraldehyde. Carboxymethylation of the enzyme did not result in the generation of several partially oxidized enzyme species, indicating the absence of partially carboxymethylated forms. Primary deuterium isotope effects on the reduced enzyme were consistent with a preferred ordered kinetic reaction scheme, in which hydride transfer is not rate limiting. The hydride transfer step does not seem to be significantly affected by carboxymethylation, nor do changes in the substrate binding steps seem to contribute to the observed rate enhancement. Increase in the turnover number of the enzyme on carboxymethylation appears to be due to facilitation of the isomerization of the E:NADP binary complex. The differential effect of carboxymethylation on sorbinil and tolrestat suggests distinct inhibitor sites on the enzyme, an S-site that binds sorbinil and a T-site that binds tolrestat.

Aldehyde Reductase↗

PubMed1992

Porous polyurethane vascular prostheses with variable compliances.

A new technique for the preparation of porous vascular prostheses was investigated. Polyurethane solution (5 to 15 wt%) was injected into a mold. After freezing at low temperature (0 degrees C-196 degrees C), solvents were dissolved out with water at 0 degrees C to form porous tubes. The average pore size (several microns to 70 microns), pore occupation (10% to 51%), and compliance (3% to 35%) were easily changed by changing polyurethane concentration, freezing temperature, and freezing methods. Compliances could be decreased gradually by heat treatment. This technique can give a proper pore size (30-60 microns) for tissue ingrowth, and a suitable compliance for matching with arteries and veins. This method might give a desired compliant graft for artificial implantation with the presently valid medical polymers.

Blood Vessel Prosthesis↗

PubMed1992

Cell growth on immobilized cell-growth factor. II. Adhesion and growth of fibroblast cells on poly(methyl methacrylate) membrane immobilized with proteins of various kinds.

The surface of poly(methyl methacrylate) membrane was partially hydrolysed and the carboxyl groups produced were coupled with various protein molecules with water-soluble carbodiimide. The immobilized proteins were a cell-growth factor insulin, cell adhesion factors fibrinogen and fibronectin, and serum proteins albumin and gamma-globulin. The insulin-immobilized poly(methyl methacrylate) membrane strongly accelerated the growth and slightly accelerated the adhesion of fibroblast cells. The immobilized fibronectin and fibrinogen enhanced the cell adhesion, and the former also accelerated the cell growth. The immobilized albumin and gamma-globulin influenced the adhesion and growth of cells very little. It was found that various proteins specifically influence the adhesion and growth of cells in an immobilized state.

Animals↗

PubMed1992

Cell growth on immobilized cell growth factor. I. Acceleration of the growth of fibroblast cells on insulin-immobilized polymer matrix in culture medium without serum.

Culture of fibroblast cells in serum-free medium in the presence of insulin-immobilized films of poly(ethylene terephthalate) or poly(methyl methacrylate) accelerated the cell growth to several times that in the presence of free insulin molecules. The immobilization of insulin was useful also for elucidation of the mechanism of signal transmission through receptor molecules in the cell membrane. Free insulin molecules are known to be bound by receptors and the complex formed internalized and degraded in the cytoplasm. However, it is not clear what process is indispensable for transmission of the biological signals to the nucleus of the cell. The present investigation revealed that cell growth was enhanced by the addition of immobilized insulins which were not internalized. It appears that insulin-receptor binding is enough for transmission of the cell growth signal to the cell nucleus. The enhanced cell growth by the immobilized insulins compared with free insulin molecules is ascribable to suppression of the down-regulation which is a consequence of intracellular decomposition of the insulin-receptor complex.

Animals↗