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S Chen

Publications and source records attributed to S Chen.

At least 1,045 records · Page 58Linked to original sources
PubMed1995

Evidence that cholera toxin B subunit (CTb) can be avidly taken up and transported by fibers of passage.

It has been reported that cholera toxin B subunit (CTb) is a sensitive neuronal tracer with unique features. However, the possible uptake of CTb by non-terminal fibers passing through the injection site has not been examined thoroughly. In the present study, small iontophoretic injections (current = +2 microA) of CTb were made in the olivocerebellar pathway in the rat ventrolateral medulla. A large number of retrogradely labeled neurons were seen in the contralateral inferior olive. In addition, prominent anterogradely labeled climbing fibers/terminals were found in the cerebellum ipsilateral to the injection site. This study, in contrast to previous report(s), indicates that CTb can be taken up avidly by fibers of passage and transported both anterogradely and retrogradely.

Animals↗
PubMed1995

Active site studies of DT-diaphorase employing artificial flavins.

NAD(P)H:quinone oxidoreductase (EC 1.6.99.2) (DT-diaphorase) is an FAD-containing enzyme that catalyzes the 2-electron reduction of quinones to hydroquinones using either NADH or NADPH as the electron donor. In this study, FAD was removed by dialyzing the holoprotein against 2 M KBr, and synthetic analogs of FAD were substituted in the flavin binding site as structural probes. Spectral analysis indicates that the benzoquinoid forms of 8-mercapto-FAD and 6-mercapto-FAD are stabilized on binding to the enzyme. This is consistent with the fact that the native flavoprotein forms the anion flavin radical upon photoreduction and suggests the presence of a positive charge near the N(1)C(2)O position of the isoalloxazine ring. Reactivity studies using 8-chloro- and 8-mercapto-flavins suggest that the 8 position of the FAD is accessible to the solvent. However, the rates of the reactions were dramatically decreased in the presence of the competitive inhibitor, dicumarol. 6-Mercapto-, 6-thiocyanato-, 6-azido-, and 6-amino-flavins were also used as structural probes. The results indicate that the 6 position is accessible to solvent. Dicumarol binding increases the pK alpha of the enzyme-bound 6-mercapto-flavin from below pH 5.0 to higher than pH 9.0. The results suggest that DT-diaphorase shows the same properties as the C-C transhydrogenases, and the binding of dicumarol elicits a conformational change or an adjustment in the polarity of the FAD pocket. The enzyme reconstituted with oxidized 5-deaza-FAD has significant catalytic activity, confirming that DT-diaphorase is an obligatory 2-electron transfer enzyme and plays a role in the detoxification of quinones and quinoid compounds by reducing them to the relatively stable hydroquinones.

Binding Sites↗
PubMed1995

Beyond hyperacute rejection. Accelerated rejection in a discordant xenograft model by adoptive transfer of specific cell subsets.

If hyperacute rejection is prevented in the guineapig (GP)-to-Lewis rat (Lew) cardiac xenograft (CXg) model, an accelerated rejection involving cellular infiltration occurs in 3 to 4 days. In previous work using an adoptive transfer model, we found that this accelerated rejection was facilitated by either sensitized splenocytes or sensitized serum. In the current study, in an attempt to determine which splenocyte subset(s) facilitated this process, sensitized splenocytes, with or without subset depletion were injected, into complement- and natural antibody-depleted Lew recipients of GP CXgs. Graft survival was 4.18 +/- 0.75 days with no injection (n = 11), 4.13 +/- 0.99 days with naive splenocytes (n = 8), 1.80 +/- 0.45 days with sensitized splenocytes (n = 5), 2.67 +/- 1.03 days with CD4(W3/25+) depletion of the sensitized splenocytes (n = 6), 3.13 +/- 0.84 days with CD8(OX8+) cell depletion (n = 8), 4.70 +/- 0.68 days with macrophage depletion (n = 10), and 4.22 +/- 0.41 days with B cell depletion (n = 9). Cellular infiltrates, hemorrhage, myocyte necrosis, and endothelial deposition of IgG, IgM, and fibrin were seen in rejected grafts. In most groups, infiltrating cells consisted of CD4 (W3/25+), CD8 (OX8+), IL2R+ cells, macrophages, and natural killer (NK) cells. However, in the macrophages-depleted group, activated (ED2+) macrophages and NK cells were significantly reduced. Total IgM, anti-GP IgM, and anti-GP IgG rebounded in all groups over several days but were not consistent at the time of rejection. Lewis rats rejecting GP CXgs early had lower final titers than those rejecting later. Total IgG titers rebounded to baseline by posttransplant day 1 and were therefore similar in all groups at the time of rejection. These findings suggest that this accelerated rejection requires interaction between macrophages and B cells, since depletion of either significantly alters the rejection tempo. A possible explanation is that xenoreactive IgG antibodies, synthesized by sensitized B cells, bind their target antigens--but also bind sensitized macrophages through their Fc region, thus causing rejection by antibody-dependent cell-mediated cytotoxicity.

Acute Disease↗
PubMed1995

DT-diaphorase. Redox potential, steady-state, and rapid reaction studies.

NAD(P)H:quinone oxidoreductase (DT-diaphorse) appears to be a 2-electron transfer flavoprotein, which catalyzes the conversion of quinones into hydroquinones. Upon photoreduction in the presence of dimethylformamide, the enzyme forms a red semiquinone. In the absence of dimethylformamide, only 10% of the radical form is thermodynamically stabilized. This indicates a redox potential of the enzyme-bound semiquinone/reduced flavin couple that is higher than the midpoint potential for the oxidized flavin/semiquinone couple. The 2-electron redox potential was determined to be -159 +/- 3 mV at 25 degrees C, pH 7.0. In the presence of benzoquinone or 3-aminopyridine adenine dinucleotide phosphate, as NADPH analogue, there is no change in the redox properties of the enzyme flavin. A significant decrease is observed in the presence of the competitive inhibitor dicumarol (Em = -234 +/- 2 mV at pH 7.0). The reaction mechanism of the flavoprotein has been investigated by steady-state and stopped-flow kinetic methods using NADPH, NADH, deamino-NADPH, and 3-acetylpyridine adenine dinucleotide reduced form (APADH) as electron donors and K3Fe(CN)6, 4,5-dihydro-4,5-dioxo-1H-pyrrolo-[2,3-f]quinoline-2,7,9-tricarboxylic acid (PQQ), and 2,5-diaziridinyl-3,6-bis(carboethoxy-amino)-1,4-benzoquinone (AZQ) as electron acceptors in 50 mM phosphate buffer, pH 7.0, 25 degrees C. No evidence could be obtained to indicate that semiquinoid intermediates play a part in the catalytic mechanism of DT-diaphorase with quinones as acceptors. The rates of the reduction by NADPH, NADH, deamino-NADPH, and APADH (1.3 x 10(9), 8.8 x 10(8), 8.3 x 10(8) and 9.8 x 10(8) m-1 min-1, respectively) as well as the rates of the reoxidation by PQQ and AZQ (9 x 10(4) and 2.8 x 10(6) M-1 min-1, respectively) are directly proportional to substrate concentration, and there is no evidence of the formation of enzyme-substrate complexes. If such complexes do indeed exist, the affinity of the enzyme for substrate must be extremely low. Using K3Fe(CN)6 as electron acceptor, the rate of oxidation of fully reduced enzyme is 4.6 x 10(7) M-1 min-1 and it is accurately proportional to ferricyanide concentration. This rate represents that of flavin semiquinone formation, with the subsequent oxidation of the semiquinone being much faster, since no spectral evidence for semiquinone formation could be obtained. Studies were also conducted attempting to use apo-DT-diaphorase reconstituted with PQQ as coenzyme. The lack of activity toward AZQ, K3Fe(CN)6, and menadione suggests that DT-diaphorase can use PQQ only as electron acceptor and not as redox cofactor.

Flavin-Adenine Dinucleotide↗
PubMed1995

Enrichment of human hematopoietic stem cell activity in the CD34+Thy-1+Lin- subpopulation from mobilized peripheral blood.

The number of CD34+ cells in the peripheral blood of cancer patients is known to be increased following the administration of high dose chemotherapy and hematopoietic growth factors. These so-called peripheral blood stem cell grafts are now frequently used for autologous transplantation of patients with malignancies. In this report, we address the question of whether true long-term repopulating pluripotent hematopoietic stem cells (PHSC) are mobilized into peripheral blood following chemotherapy plus granulocyte/macrophage colony-stimulating factor (GM-CSF) or granulocyte colony-stimulating factor (G-CSF) mobilization. We have examined the presence of stem cells in mobilized peripheral blood (MPB) by using an antibody to the human Thy-1 molecule to stain the CD34+Lineage- (Lin-) population. The kinetics of mobilization of CD34+Thy-1+ Lin- cells into peripheral blood were studied, and the percentage of cells with this phenotype was found to vary widely depending on the day of leukapheresis. A CD34+Thy-1+Lin- cell population, potentially containing PHSCs, was isolated by fluorescence activated cell sorting (FACS) and analyzed for activity. The multilineage differentiative capacity of this candidate stem cell-containing population in MPB was determined using an in vitro long-term culture system, in which cobblestone area formation was used as a means of detecting PHSCs. We also measured repopulating capacity by using two in vivo models in which severe combined immunodeficiency (SCID)-hu mice were implanted with human fetal bone or thymus grafts. Using these assays, we show that the highest frequency of cobblestone area-forming cells (CAFC) after 7 weeks of culture was observed in a subpopulation of CD34+Lin- cells, which expressed low levels of Thy-1. This cell population was capable of producing both B and myeloid cells, and maintaining CD34+Lin- cells in these long term cultures. Moreover, the CD34+Thy-1+Lin- cell subset possessed a higher ability to engraft and to demonstrate multilineage differentiative potential at 8 weeks in the SCID-hu bone assay. However, in the SCID-hu thymus model, both Thy-1+ and Thy-1- subpopulations were capable of donor T-cell engraftment at 6 weeks, suggesting the presence of cells capable of initiating T lymphopoiesis in both populations.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Lysophosphatidylcholine causes Ca2+ influx, enhanced DNA synthesis and cytotoxicity in cultured vascular smooth muscle cells.

The effects of lysophosphatidylcholine (LPC), a vasoactive phospholipid, on intracellular free calcium concentration ([Ca2+]i), DNA synthesis and cytotoxicity of vascular smooth muscle cells (VSMC) were studied. LPC from 10(-7) to 10(-5) mol/l dose-dependently induced a sustained increase in [Ca2+]i. In contrast to the response of [Ca2+]i induced by angiotensin II, that induced by LPC was totally abolished when extracellular Ca2+ was removed, was not affected by pretreatment of the cells with islet-activating protein, and was not desensitized by repeated addition. 8-(N,N-Diethylamino)octyl 3,4,5-trimethoxybenzoic acid (TMB-8), an inhibitor of Ca2+ release from intracellular Ca2+ stores, 1-(5-isoquinolinesulfonyl)-2-methylpiperadine dihydrochloride (H-7), an inhibitor of protein kinase C, KT5823, an inhibitor of protein kinase G, and Ca2+ channel blockers failed to suppress the LPC-induced increase in [Ca2+]i. LPC at 10(-5) mol/l caused significant stimulation of [3H]thymidine incorporation into VSMC, and at concentrations of 10(-5) mol/l and higher dose-dependently stimulated release of lactate dehydrogenase in cell culture supernatants. Moreover, digitonin mimicked the effects of LPC on [Ca2+]i, and also caused similar effects to those of LPC on DNA synthesis and cytotoxicity in VSMC. These observations suggest that LPC causes both cell growth and cell injury of VSMC, at least partly, through its detergent action, causing membrane leakiness and resultant [Ca2+]i overload in vitro, thus indicating the possible participation of LPC in atherosclerosis and/or injury of the vascular wall.

Animals↗
PubMed1995

Gene expression of retinoic acid receptors and cellular retinoic acid-binding proteins in rhino and hairless mouse skin.

The rhino mouse comedolytic model and the hairless mouse photoaging model are established animal models for screening the in vivo activity of retinoids. However, the expression of the retinoic acid receptors (RARs) and cellular retinoic acid-binding proteins (CRABPs), known to regulate retinoid activity, is not completely understood in these mouse mutants. For this purpose, mRNA was isolated from rhino and hairless mouse skin and the gene expression of the RARs and CRABPs was measured by Northern blot hybridization. Results showed that RAR gamma was the predominantly expressed RAR in both mouse strains. Two isoforms of RAR gamma, RAR gamma 1 and RAR gamma 2, were detected with RAR gamma 1 being the more strongly expressed. RAR alpha was also detected, but to a lesser degree than RAR gamma. RAR beta expression was not detectable by our methodology. Additionally, topical treatment of these mice with 0.1% all-trans-retinoic acid (tRA) cream resulted in no significant alteration in the expression of the RAR genes. By contrast, CRABP-II was induced 2-4 fold by topical tRA treatment. CRABP-I, expressed to a lesser degree than CRABP-II, was not inducible. The relative expression of the RARs, CRABPs, and inducibility of CRABP-II by tRA in both rhino and hairless mouse skin paralleled that reported for human and mouse skin. These observations suggest that the altered phenotype observed in the rhino mouse most likely does not result from an altered expression level of these genes. The results also support these two animals as models for evaluating the therapeutic potential of retinoids.

Animals↗
PubMed1995

Electron microscopic localization of ATPase activity in tobacco cells infected by tobacco etch potyvirus and tobacco mosaic virus.

Thin sections of leaves of plants infected by tobacco etch potyvirus (TEV) or tobacco mosaic virus (TMV) were examined for the presence of ATPase activity by electron microscopy. ATPase activity was found as expected in mitochondria, chloroplasts and plasmalemma of both uninfected as well as cells infected by either TEV or TMV. In the TEV-infected cells, ATPase activity was localized to virus-induced vesicles, endoplasmic reticulum and in some cells, to ribosomes attached to the ER. In TMV-infected cells, ATPase activity was found in vesicles as well as in tubular membranes closely associated with the X-bodies.

Adenosine Triphosphatases↗
PubMed1995

A target in real motion appears blurred in the absence of other proximal moving targets.

For exposure durations longer than about 40 msec, a field of dots in sampled motion has been reported to appear less smeared than predicted from the visual persistence of static displays. This reduction of perceived smear has been attributed to a motion "deblurring" mechanism. However, it has been long recognized that an isolated target moving continuously in a dark field appears to be extensively smeared. To reconcile these apparently contradictory observations, we investigated the effect of dot density on the extent of perceived smear for a single moving dot and for fields of dots with densities ranging from 0.75 to 7.5 dots/deg2. Bright targets were presented in continuous motion against a photopically illuminated background field. The results reconcile previous conflicting observations by showing that the length of perceived smear decreases systematically with dot density for exposure durations longer than about 50 msec. In three additional experiments, we arranged the spatial configuration of the targets to evaluate whether motion deblurring results primarily from a motion compensation mechanism (such as integration within the spatiotemporally oriented receptive fields of putative motion mechanisms) or from inhibition exerted by spatiotemporally adjacent targets. The results show that the activation of motion mechanisms is not a sufficient condition for motion deblurring and that the reduction of perceived smear requires the presence of spatiotemporally adjacent targets. Taken together, these findings suggest that motion deblurring results primarily from masking exerted by spatiotemporally proximal targets.

Afterimage↗
PubMed1995

A sensitive double immunostaining protocol for Fos-immunoreactive neurons.

Immunostaining of Fos, the nuclear protein encoded by the immediate early gene c-fos, is widely used to reveal the functional activation of neurons. The chemical identity of cells that express c-fos can be investigated with double immunohistochemistry. We report the usefulness of a sequential two-color avidin-biotin-immunoperoxidase method that provides a highly sensitive double immunostaining and allows long-term storage of the sections. In this protocol, metal intensification of diaminobenzidine (int-DAB) resulted in dark brown/black Fos immunostaining of the neuronal nucleus. The use of alpha-naphthol/pyronin reaction product yielded pink immunostaining of a second antigen in the cytoplasm. This combination produced higher contrast than that produced by int-DAB Fos immunostaining combined with conventional DAB light brown cytoplasmic staining. The sensitivity of the use of int-DAB and alpha-naphthol/pyronin was verified in different experimental paradigms, combining the immunocytochemical detection of Fos with that of the p75 nerve growth factor receptor, or parvalbumin, or calbindin D28k.

Ammonium Sulfate↗
PubMed1995

Characterization of fractured permeable porous media using relaxation-weighted imaging techniques.

The inversion time (TI) weighted inversion-recovery spin-echo (IRSE) imaging technique was used for laboratory characterization of fractures and porous matrix in permeable media. The method is based on the fact that relaxation rates in fractures and those in surrounding porous matrix are substantially different. Thus, by selectively suppressing imaging signals from either fractures or porous matrix, one can highlight fluid distributions in either of these regions so that fractures can be unambiguously identified and surrounding porous structures can be characterized. The advantages over conventional NMR spin-echo imaging are demonstrated with various fractured porous rock types. A technique to speed acquisitions of images of fluid distributions in porous matrix is also demonstrated.

Calcium Carbonate↗
PubMed1995

Characterization of enhanced 45Ca2+ efflux in cultured vascular smooth muscle cells from spontaneously hypertensive rats.

In this study we have compared Ca2+ efflux in cultured aortic smooth muscle cells derived from male, 10-week-old spontaneously hypertensive and Wistar-Kyoto rats. The role of Ca(2+)-dependent protein kinase C and Ca2+ uptake in the regulation of the Ca2+ pump and Na(+)-Ca2+ exchange mediated Ca2+ efflux were investigated. Basal, angiotensin II, and ionomycin-stimulated Ca2+ effluxes were significantly higher in spontaneously hypertensive rats. Brief (5 min) or prolonged (3 h) incubation of the cells with 100 nmol/L 12-O-tetradecanoylphorbol-13-O-acetate (TPA), a protein kinase C stimulator, did not significantly affect the maximum Ca2+ efflux rate in either strain. However, the Ca2+ efflux rates at early timepoints in Wistar-Kyoto rats were increased by TPA, but not in spontaneously hypertensive rats. Incubation of cells with [45Ca]-labeled CaCl2 in balanced salt solution for 4 h led to greater Ca uptake in spontaneously hypertensive rats compared to Wistar-Kyoto controls. Verapamil (1 mumol/L) for 4 h reduced the cellular Ca content of spontaneously hypertensive rats by 30% to the level of Wistar-Kyoto rats; it also reduced the Ca content in Wistar-Kyoto rats, but to a lesser extent (18%). In parallel, Ca2+ efflux was also reduced by verapamil to a greater extent in spontaneously hypertensive rats than in Wistar-Kyoto rats. We conclude that Ca2+ efflux was enhanced in spontaneously hypertensive rats by a mechanism partly associated with greater Ca2+ uptake by a verapamil-sensitive pathway and possibly an alteration of protein kinase C regulation. However, an up-regulation of the number or efficiency of Ca2+ efflux sites may also significantly contribute as an adaptive response to enhanced Ca2+ influx.

Animals↗
PubMed1995

Protracted posttraumatic optic disc swelling.

BACKGROUND: Optic disc swelling is a rare sequela of blunt ocular trauma. METHODS: The authors examined three young patients who had an unusual post-traumatic optic neuropathy in which protracted swelling of the optic nerve head was the salient clinical feature. RESULTS: Associated choroidal ruptures in two patients suggested a contrecoup mechanism of injury to the optic nerve at its junction with the globe. All patients had partial recovery of vision over months, concurrent with resolution of the nerve head swelling and development of optic disc pallor. CONCLUSION: Despite its protracted course, posttraumatic optic disc swelling appears to be associated with a favorable prognosis for visual recovery.

Adolescent↗
PubMed1995

Transference in social perception: the role of chronic accessibility in significant-other representations.

Research has shown that the activation and application of a significant-other representation to a new person, or transference, occurs in everyday social perception (S. M. Andersen & A. Baum, 1994; S. M. Andersen & S. W. Cole, 1990). Using a combined idiographic and nomothetic experimental paradigm, two studies examined the role of chronic accessibility of significant-other representations in transference. After learning about 4 fictional people, 1 of whom resembled a significant other, participants' recognition memory was assessed. Both studies showed greater false-positive memory in the significant-other condition, relative to control, even in the absence of priming. Study 2 showed that although the effect was greater when the significant-other representation was concretely applicable to the target information, it occurred even when no such applicability was present. Results implicate the chronic accessibility of significant-other representations in transference.

Adolescent↗
PubMed1995

Serial learning with a wild card by pigeons (Columba livia): effect of list length.

Pigeons (Columba livia) learned 3-, 4- or 5-item lists prior to subset and wild card tests. On the latter, a novel item replaced 1 of the list items. Pigeons who learned 3-item lists responded accurately on all subset pairs (AB, BC, and AC) and on all types of 3-item wild card trials (WBC, AWC, & ABW). Pigeons who learned 4- and 5-item lists responded at chance levels of accuracy on all subsets that did not contain a start or an end item (BC, BD, & CD, respectively, on 4- and 5-item subset tests). On wild card trials, they exceeded chance levels of performance only when the wild card replaced the last item (ABCW & ABCDW trials). Monkeys (Cebus apella) trained to produce a 5-item list perform accurately on all subsets and wild cards. (M. R. D'Amato & M. Colombo, 1988, 1989). These differences provide strong evidence that pigeons and monkeys form qualitatively different representations of lists containing four or more items.

Animals↗