PubMed Health⌕ Search

Biomedical subjects

S Q Liu

Publications and source records attributed to S Q Liu.

At least 55 records · Page 3Linked to original sources
PubMed1997

The role of cytoskeletal elements in the two-phase denucleation process of mammalian erythroblasts in vitro observed by laser confocal scanning microscope.

The cytoskeletal elements in the denucleation processes were observed using immunofluorescence and laser confocal scanning microscopy in the Friend virus (FVA) infected splenic erythroblasts of BALB/c mice. When cultured in the presence of erythropoietin (EPO), it was shown that the synchronized erythroid precursor cells proceeded to an autonomous nuclear extrusion when the three types of cytoskeletal elements were observed contributing to different phases of that process. The vimentin intermediate filament (IF) was shown as the nuclear anchorage elements with binding sites anchored from the nuclear lamina to the center as well as to the plasma membrane periphery. A dense perinuclear layer of vimentin fluorescence in erythroblasts was observable during the periods of 12, 24 and 36 hrs. in vitro culture. The amount of vimentin IF per cell was higher than that of tubulin and F-actin at 12-24 hrs. culture, but the vimentin filaments were observed to brake down and decreased steadily when the cells became differentiated into late erythroblasts at 36-48 hrs. Such an attenuation of vimentin filaments may facilitate the eccentric movement of the nucleus which can be regarded as the initial step (phase) of denucleation. The fluorescent intensity of tubulin and actin exhibited a significant rise and aggregated between the extruding nucleus and the incipient reticulocyte prior to and during the processes of denucleation, what indicated that the actin filaments and microtubules may play roles in the second phase of the denucleation process, or final commitment of enucleation. The erythroid differentiation-denucleation factor (EDDF), as an intrinsic factor, involved in the denucleation events, was also discussed.

Animals↗
PubMed1996

Interaction between ryanodine and neomycin binding sites on Ca2+ release channel from skeletal muscle sarcoplasmic reticulum.

Neomycin is a potent inhibitor of skeletal muscle sarcoplasmic reticulum (SR) calcium release. To elucidate the mechanism of inhibition, the effects of neomycin on the binding of [3H]ryanodine to the Ca2+ release channel and on its channel activity when reconstituted into planar lipid bilayer were examined. Equilibrium binding of [3H]ryanodine was partially inhibited by neomycin. Inhibition was incomplete at high neomycin concentrations, indicating noncompetitive inhibition rather than direct competitive inhibition. Neomycin and [3H]ryanodine can bind to the channel simultaneously and, if [3H]ryanodine is bound first, the addition of neomycin will slow the dissociation of [3H]ryanodine from the high affinity site. Neomycin also slows the association of [3H]ryanodine with the high affinity binding site. The neomycin binding site, therefore, appears to be distinct from the ryanodine binding site. Dissociation of [3H]ryanodine from trypsin-treated membranes or from a solubilized 14 S complex is also slowed by neomycin. This complex is composed of polypeptides derived from the carboxyl terminus of the Ca2+ release channel after Arg-4475 (Callaway, C., Seryshev, A., Wang, J. P., Slavik, K., Needleman, D. H., Cantu, C., Wu, Y., Jayaraman, T., Marks, A. R., and Hamilton, S. L. (1994) J. Biol. Chem. 269, 15876-15884). The proteolytic 14 S complex isolated with ryanodine bound produces a channel upon reconstitution into planar lipid bilayers, and its activity is inhibited by neomycin. Our data are consistent with a model in which the ryanodine binding sites, the neomycin binding sites, and the channel-forming portion of the Ca2+ release channel are located between Arg-4475 and the carboxyl terminus.

Animals↗
PubMed1996

Effects of external pH on substrate binding and on the inward chloride translocation rate constant of band 3.

To test the hypothesis that amino acid residues in band 3 with titratable positive charges play a role in the binding of anions to the outside-facing transport site, we measured the effects of changing external pH (pH(O)) on the dissociation constant for binding of external iodide to the transport site, K(O)(I). K(O)(I) increased with increasing pH(O), and a significant increase was seen even at pH(O) values as low as 9.9. The dependence of K(O)(I) on pH(O) can be explained by a model with one titratable site with pK 9.5 +/- 0.2 (probably lysine), which increases anion affinity for the external transport site when it is in the positively charged form. A more complex model, analogous to one recently proposed by Bjerrum (1992), with two titratable sites, one with pK 9.3 +/- 0.3 (probably lysine) and another with pK > 11 (probably arginine), gives a slightly better fit to the data. Thus, titratable positively charged residues seem to be functionally important for the binding of substrate anions to the outward-facing anion transport site. In addition, analysis of Dixon plot slopes for L inhibition of Cl- exchange at different pH 0 values, coupled with the assumption that pH(O) has parallel effects on external I- and Cl- binding, indicates that k', the rate-constant for inward translocation of the complex of Cl- with the extracellular transport site, decreases with increasing pH(O). The data are compatible with a model in which titration of the pK 9.3 residue decreases k to 14 +/- 10% of its value at neutral pH(O). This result, however, together with Bjerrum's (1992) observation that the maximum flux J(M)) increases 1.6-fold when this residue is deprotonated, makes quantitative predictions that raise significant questions about the adequacy of the two titratable site ping-pong model or the assumptions used in analyzing the data.

Allosteric Regulation↗
PubMed1996

Effects of external pH on binding of external sulfate, 4.4-dinitro-stilbene-2,2'-disulfonate (DNDS), and chloride to the band 3 anion exchange protein.

A model in which two positively-charged titratable sites enhance the affinity for anionic substrates can explain the increase in external iodide dissociation constant (K(O)(I)) with increasing pH(O) (Liu, S. J., F.-Y. Law, and P.A. Knauf. 1996.f Gen.Physiol. 107:271-291). If sulfate binds to the same external site as I-, this model predicts that the SO(4)= dissociation constant (K(O)(S)) should also increase. The data at pH 0 8.5 to 10 fit this prediction, and the pK for the titration is not significantly different from that (pKc) for the low-pK group that affects K(O)(1). The dissociation constant for the apparently competitive inhibitor, DNDS (4,4-dinitrostilbene-2,2'-disulfonate), also increases greatly as pH(O) increases. Particularly at high pH(O), a noncompetitive inhibition by DNDS is also evident. Increasing pH(O) from 7.2 to 11.2 increases the competitive dissociation constant by 700-fold, but the noncompetitive is only increased 20-fold. The pK values for these effects are similar to pKc for K(O)(1), as expected if DNDS binds near the external transport site, but it seems likely that additional titratable groups also affect DNDS binding. The apparent affinity for external Cl- is also affected by pH(O), in a manner similar to that observed for I-. Pretreatment with the amino-selective reagent, bis-sulfosuccinimidyl suberate (BSSS), decreases the apparent Cl- affinity at pH 8.5, but two titrations are still evident, the first (lower) of which decreases the apparent C- affinity, and the second of which surprisingly increases it. Thus, the BSSS-reactive amino groups (probably Lys-539 and Lys-851) do not seem to be involved in the titrations that affect Cl- affinity. In general, the data support the concept that a positively charged amino group (or groups), together with a guanidino group, plays an important role in the binding of substrates and inhibitors at or near the external transport site.

Amino Acids↗
PubMed1996

Indicial functions of arterial remodeling in response to locally altered blood pressure.

We investigated the effect of locally altered blood pressure on the remodeling processes of the cells and extracellular matrices of the splenic and ileal arteries and used an indicial function approach to quantitatively analyze the relationship between the altered blood pressure and the remodeling processes. Blood pressure in these arteries was locally modulated by constricting the aorta at a location between the celiac and mesenteric bifurcations, resulting in a higher blood pressure at the splenic arteries then at the ileal arteries, After the pressure changes, the cross-sectional areas and the fractions of the cells and extracellular matrices of the splenic and ileal arteries were examined by electron microscopy at 2, 6, 10, 20, and 30 days. We found that both arteries remodeled, but the splenic arteries (higher blood pressure) remodeled more rapidly and to a larger degree than the ileal arteries (lower pressure compared with the splenic arteries) of the same animal. To verify whether an identical change in the blood pressure at the splenic and ileal arteries leads to the same remodeling process in these arteries, we created another model by constricting the aorta at a location between the mesenteric and renal bifurcations, resulting in hypertension of the same level at both splenic and ileal arteries. We found that the remodeling processes of the cells and matrices were almost identical in the arteries with similar changes in blood pressure. Thus we conclude that the remodeling processes of cells and matrices of the splenic and ileal arteries are dependent on the local blood pressure in aorta constriction-induced hypertension, and the indicial analysis is a useful approach in the description of the relationship between the blood pressure and the arterial remodeling processes.

Animals↗
PubMed1996

Alterations in structure of elastic laminae of rat pulmonary arteries in hypoxic hypertension.

The effect of hypoxic hypertension on the remodeling process of the elastic laminae of the rat hilar pulmonary arteries (PAs) was studied by electron microscopy. Rats were exposed to hypoxia (10% O2) for periods of 0.5, 2,6,12,48,96,144, and 240 h. Changes in the structure of the PA elastic laminae were examined and analyzed with respect to changes in the PA wall tensile stress. The PA blood pressure increased rapidly within the first several hours of hypoxia and reached a stable level within 2 days, whereas the PA wall tensile stress increased initially due to elevated blood pressure and then decreased after 48 h due to vessel wall thickening and returned to the control level after 4 days. In association with these changes, the elastic laminae, which appeared homogeneous in normal control rats, changed into structures composed of randomly oriented filaments and edematous contents with an increase in the volume during the early period of hypoxia and regained their homogeneous appearance and normal volume after 4 days. The changes in the elastic laminae were correlated with changes in the tensile stress. These changes were associated with a transient decrease in the stiffness of the PAs. In hypoxic rats given nifedipine, no change was found in the blood pressure, the tensile stress, or the structure of the elastic laminae of the PAs despite continuous exposure to hypoxia. These results suggested that altered tensile stress in the PA wall played a critical role in the initiation and regulation of structural changes in the elastic laminae and that these changes might contribute to alterations in the mechanical properties of the PA in hypoxic hypertension.

Animals↗
PubMed1996

Induction of human autologous cytotoxic T lymphocytes against minced tissues of glioblastoma multiforme.

The authors induced autologous cytotoxic T lymphocytes (CTLs) directly from peripheral blood lymphocytes by preparing a coculture of minced tissue fragments of glioblastoma multiforme (GBM) with interleukins-1, -2, -4, and -6 and interferon-gamma in RHAM alpha medium containing 5% autologous plasma for 2 weeks. At the end of this period, the frequencies of CD3+, CD4+, CD8+, and CD16+ lymphocytes were 95% to 99%, 40% to 62%, 37% to 38%, and 0.2%, respectively. The lymphocytes killed 82% to 100% of the GBM cells within 48 hours at an effector-to-target cell ratio of 1.67, whereas in a separate coculture, autologous lymphokine-activated killer (LAK) cells killed only 33% of GBM cells under the same conditions. The lymphocytes showed no cytotoxicity against LAK-sensitive Daudi cells, natural killer-sensitive K562 cells or autologous fibroblasts grown from the brain tumor, although they did show slight cytotoxicities against allogeneic GBM cell lines. These results lead the authors to suggest that the lymphocyte population contains specific CTLs for autologous brain tumor cells and that these CTLs could be effective in adoptive immunotherapy to combat brain tumor.

Adult↗
PubMed1995

Determination of the mechanical properties of the different layers of blood vessels in vivo.

The structure and materials of the blood vessel wall are layered. This article presents the principle of a method to determine the mechanical properties of the different layers in vivo. In vivo measurement begets in vivo data and avoids pitfalls of in vitro tests of dissected specimens. With the proposed method, we can measure vessels of diameters 100 microns and up and obtain data on vascular smooth muscles and adventitia. To derive the full constitutive equations, one must first determine the zero-stress state, obtain the morphometric data on the thicknesses of the layers, and make mechanical measurements in the neighborhood of the zero-stress state. Then eight small perturbation experiments are done on earth blood vessel in vivo to determine eight incremental elastic moduli of the two layers of the blood vessel wall. The calculation requires the morphometric data and the location of the neutral axis. The experiments are simple, the interpretation is definitive, but the analysis is somewhat sophisticated. The method will yield results that are needed to assess the stress and strain in the tissues of the blood vessel. The subject is important because blood vessels remodel themselves significantly and rapidly when their stress and strain deviate from their homeostatic values, and because cell proliferation, differentiation, adhesion, contraction, and locomotion depend on stress and strain in the tissue.

Animals↗
PubMed1995

Induction of human autologous cytotoxic T lymphocytes on formalin-fixed and paraffin-embedded tumour sections.

Human autologous tumour-specific cytotoxic T lymphocytes (CTL) were generated from peripheral blood on small formalin-fixed paraffin-embedded sections of a gastric cancer. The CTL killed live target cells at an effector/target ratio of 1 within 24 hours and showed the same target specificity as those induced on live cancer cells. The killing activity of the CTL lasted for more than four months in culture and was inhibited by antibodies against CD8 and MHC-class I. These results suggest that adoptive immunotherapy of tumours will be possible with CTL induced on a stable source of tumour antigen.

Adenocarcinoma↗
PubMed1995

Detection of 54-kDa protein overexpressed by chloroquine-resistant Plasmodium berghei ANKA strain in pyronaridine-resistant P berghei ANKA strain.

AIM: A 54-kDa protein overexpressed by chloroquine-resistant (CR) Plasmodium berghei ANKA strain was first reported by us. This study is conducted to detect the protein in pyronaridine-resistant (PR) P berghei ANKA strain. METHODS: Immunoblotting analysis and immunoelectron microscopy were used. RESULTS: PR parasites, like CR parasites, mainly overexpressed 2 major bands of 37 (36-38) kDa and 16 (15-17) kDa which were considered to be 2 subunits of 54 (52-62) kDa protein. Three of 7 times of experiments showed a 54-kDa and a 96 (95-100) kDa bands. The proteins were localized to be mainly scattered in cytoplasm of trophozoites, schizonts, and merozoites of erythrocytic stage of P berghei. Some of them were distributed in cytoplasm of erythrocytes infected with parasites. CONCLUSION: Both PR and CR parasites overexpressed the same proteins.

Animals↗
PubMed1994

On measuring the third dimension of cultured endothelial cells in shear flow.

The stress in the endothelial cells induced by blood flow depends on the waviness of the blood-endothelium interface and the slopes at the junctions of neighboring cells in the direction of flow. The height and slope in the third dimension of the living endothelial cells cannot be measured by ordinary optical and electron microscopy. Here we show that interference microscopy meets the challenge. We measured the geometry of cultured confluent human vascular endothelial cells in a flow, and we found that in a normal section parallel to the flow, the absolute values of the surface slopes at the cell junctions were 0.70 +/- 0.02 (SE) and 0.80 +/- 0.02 (SE) at the leading and trailing edges of the cells, respectively, in a culture medium of osmolarity 310 mosM with a shear stress of approximately 1 N/m2. A reversal of the flow direction led to a reversal of the slope pattern. An increase in medium osmolarity above 310 mosM induced an initial decrease in the slopes followed by a return to normal, whereas a decrease in the osmolarity had a reversed effect. These results, in light of our previous theoretical analyses, show that tensile stress exists in the endothelial cell membrane, and that the mechanism of tension accumulation is a reality. The accumulation is not 100% because the membranes are not smooth at the cell junctions.

Blood Viscosity↗
PubMed1994

Human placental aldose reductase: role of Cys-298 in substrate and inhibitor binding.

Steady-state kinetic and inhibition properties of human placental aldose reductase carboxymethylated at Cys-298 were investigated. A comparison of the primary deuterium kinetic isotope effect on the reduced and the carboxymethylated enzymes suggests that carboxymethylation did not affect the reaction sequence of substrate binding and release. Values of DV/KD-glyceraldehyde greater than DV suggest that steps in the reaction scheme subsequent to hydride transfer, particularly the release of NADP may be rate limiting. Carboxymethylation of Cys-298 was also found to affect NADPH and aldehyde binding to the enzyme. Carboxymethylation had little effect on the secondary structure of the enzyme, but a comparison of the circular dichroic spectra of the reduced and carboxymethylated enzyme, suggests a weakened interaction between the nicotinamide and 2'-monophosphoadenosine 5'-diphosphoribose of NADPH, and the carboxymethylated enzyme. Interaction between Cys-298 and NADPH appears to determine the rate of isomerization of the E:NADP binary complex and carboxymethylation-induced decrease in kcat may be due to slower isomerization of the E:NADP binary complex. The carboxymethylated enzyme was less sensitive than the reduced enzyme to most aldose reductase inhibitors including sorbinil (d-6-fluoro-spiro[chroman-4,4'-imidazolidine]-2',5'-dione), except tolrestat (N-methyl-N-[(5-trifluromethyl-6-methoxy-1-naphthalenyl)- thiomethyl]glycine) and quercetin. On the basis of these observations it is suggested that Cys-298 may form a part of the 'S'-inhibitor binding site of the enzyme and may be responsible for tight binding of NADPH.

Aldehyde Reductase↗
PubMed1994

Long-term serum/plasma-free culture of human cytotoxic T lymphocytes induced from peripheral blood mononuclear cells.

Tumor-specific human cytotoxic T lymphocytes (CTL) were induced by co-culturing peripheral blood mononuclear cells with X-ray-irradiated human lung squamous carcinoma cells, SQ-5, in the medium supplemented with interleukin(IL)-1, IL-2, IL-4 and IL-6, and 5% autologous plasma for 3 or 5 days. The CTL grew in serum/plasma-free medium containing these four interleukins and 0.5% bovine serum albumin for over a month and maintained killing activity of target cells within 48 h at an effector/target ratio of 1.25. Their growth was essentially dependent on the target SQ-5 cells, which were renewed every 5 days. Under these conditions, IL-4 and IL-6 could be omitted. When anti-CD3 monoclonal antibody was added to the serum/plasma-free medium supplemented with IL-1 and IL-2, the target tumor cells were not required to maintain the specific killing activity of the CTL. A large number of CTL (10(11)) were obtained in 35 days.

Carcinoma, Squamous Cell↗
PubMed1994

[An immunohistochemical study on megakaryocytes in patients with myelodysplastic syndromes].

An immunohistochemical study was performed on trephine biopsy specimens of bone marrow in 10 patients with myelodysplastic syndromes (MDS). Monoclonal antibodies HIP7 and CDW41 were used against platelet glycoprotein IIb/IIIa (CD41) to determine dysmegakaryopoiesis including its size, proportion of micromegakaryocytes, location and staining characteristics. The results show that the dysmegakaryopoiesis of MDS includes the increased number and high proportion of micromegakaryocytes, the altered architectural distribution and the considerable variation in staining. These may be helpful in the diagnosis and differential diagnosis of MDS.

Bone Marrow↗
PubMed1993

Bovine lens aldose reductase. pH-dependence of steady-state kinetic parameters and nucleotide binding.

The pH-dependence of nucleotide binding and steady-state kinetic parameters of aldehyde reduction and alcohol oxidation catalyzed by bovine lens aldose reductase were studied. The maximal velocity of aldehyde reduction with NADPH and p-chlorobenzaldehyde was pH independent at low pH but decreased at high pH with a pK of 7.6. The V/K of NADPH displayed a bell-shaped dependence on pH and decreased with a pKa of 5.3 and a pKb of 7.5. The dissociation constant of NADPH and 3-acetylpyridine adenine dinucleotide phosphate (3-APADP) increased at low pH with a pK of 5.6-5.8 and at high pH with a pK of 9.4-9.7. The pKi of NADP and NADPH decreased below a pH of 5 and 6.7 and above a pH of 8.5 and 9.7, respectively. The pK of 8.5-9.7 appears to be due to the interaction of the 2'-phosphate of the nucleotide with a protonated base, possibly a lysine residue. The maximal velocity of alcohol oxidation was pH independent at high pH but decreased at low pH with a pK of 6.5-7.0, when p-chlorobenzyl alcohol or benzyl alcohol and 3-APADP were used. The amino acid residue for alcohol binding has a pK of 7.5-8.2 and also appears in pKi profiles of sorbinil, a competitive inhibitor versus the alcohol. Large (3-3.5) isotope effects on maximal velocity obtained with benzyl alcohol and 3-APADP suggest that with these substrates the hydride transfer step is rate-limiting and a pK of 6.5-7.0 may be the true pK of the acid-base catalyst, possibly a histidine.

Aldehyde Reductase↗
PubMed1993

Identification of the reactive cysteine residue in human placenta aldose reductase.

Modification of human placental aldose reductase by iodoacetate (IAA) led to a mol/mol binding of IAA, a 40% decrease in the kcat, a 3-5-fold increase in the Km,NADPH and Km,glyceraldehyde and a 600-fold increase in the Ki,sorbinil; determined at pH 6.0. NADPH and 2'-monophosphoadenosine 5'-diphosphoribose but neither glyceraldehyde nor sorbinil, prevented carboxymethylation-induced changes. Cleavage of [14C]IAA-modified enzyme by trypsin resulted in two radiolabeled peptides: Val-297 to Lys-307 and Val-297 to Phe-315. In both these peptides Cys-298 was the only radiolabeled residue. It is suggested that Cys-298 regulates the kinetic and inhibition properties of the enzyme, but does not participate in catalysis.

Adenosine Diphosphate Ribose↗