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S Shen

Publications and source records attributed to S Shen.

At least 199 records · Page 11Linked to original sources
PubMed1993

A preliminary study of the fixation mechanism of collagen reaction with a polyepoxy fixative.

A new biomaterial has been developed by fixing native collagens with a polyepoxy compound (PC) fixative. Prior studies have shown that this biomaterial has comparable properties as compared to collagen fixed with glutaraldehyde (GA) and thus has a great promise for use as an implantable bioprosthesis. The purpose of this study was to understand the mechanism of the amino acids-PC reactions in the fixation process. Bovine arteries were fixed with PC under various pH, concentration and temperature conditions as a function of fixation time. Individual amino acid components in the fresh and the fixed arteries were assayed using a Beckman amino acid analyzer to determine the degree of tanning. The denaturation temperature (Td) was also measured on each sample. Since the denaturation temperature is a direct indication of cross-linking of individual amino acids with the fixative, the difference in the degree of tanning for the same increase in Td may be indicative of the quantity of the masked, non-cross-linked amino acids. The fixation reaction data indicated that not all amino acids were cross-linked upon contacting the PC fixative. Masking appeared to be more substantial with a fixation at higher pH values.

Amino Acids↗
PubMed1992

The role of cytochrome P450 lysine residues in the interaction between cytochrome P450IA1 and NADPH-cytochrome P450 reductase.

Cytochrome P450IA1 (purified from hepatic microsomes of beta-naphthoflavone-treated rats) has been covalently modified with the lysine-modifying reagent acetic anhydride. Different levels of lysine residue modification in cytochrome P450IA1 can be achieved by varying the concentration of acetic anhydride. Modification of lysine residues in P450IA1 greatly inhibits the interaction of P450IA1 with NADPH-cytochrome P450 reductase. Modification of 1.0 and 3.3 mol lysine residues per mole P450IA1 resulted in 30 and 95% decreases, respectively, in 7-ethoxycoumarin hydroxylation by a reconstituted P450IA1/reductase complex. However, modification of 3.3 mol lysine residues per mole P450IA1 decreased only cumene hydroperoxide-supported P450-dependent 7-ethoxycoumarin hydroxylation by 30%. Spectral and fluorescence studies showed no indication of global conformational change of P450IA1 even with up to 8.8 mol lysine residues modified per mole P450IA1. These data suggest that at least three lysine residues in P450IA1 may be involved in the interaction with reductase. Identification of lysine residues in P450IA1 possibly involved in this interaction was carried out by [14C]acetic anhydride modification, trypsin digestion, HPLC separation, and amino acid sequencing. The lysine residue candidates identified in this manner were K97, K271, K279, and K407.

Acetic Anhydrides↗
PubMed1992

Embryonic stem cells stably transfected with mRAR beta 2-lacZ exhibit specific expression in chimeric embryos.

Using the embryonic stem (ES) cell/chimera approach, we have studied the activity of the mouse retinoic acid receptor beta 2 (mRAR beta 2) promoter during ES cell differentiation and during embryonic development. Stable ES clones were isolated after introduction of a 1.8 kb mRAR beta 2-lacZ expression cassette. LacZ expression in these stable clones was specifically induced by retinoic acid (RA) in a similar fashion as the endogenous RAR beta 2 gene. Following introduction of three different ES clones into blastocysts, an integration-independent mRAR beta 2-lacZ expression pattern was obtained in chimeric embryos similar to that described by in situ hybridization and transgenic studies. Moreover, mRAR beta 2-lacZ expression was also detected at some additional sites not described before, e.g. body wall, ureter, mesonephric duct and optic stalk. Maternal RA administration at 8.5 days of pregnancy extended lacZ expression to more anterior and posterior regions. Transgenic mice were generated from germ-line transmission of the transfected ES cells; expression pattern and changes in expression upon RA induction in these transgenic embryos were identical to those in chimeric embryos. We conclude that by using the ES/chimera approach, the proximal 1.8 kb of the mRAR beta 2 promoter produces a reliable and reproducible expression pattern of the reporter gene, and that the ES cell/chimera approach is invaluable for the study of gene expression and regulation.

Animals↗
PubMed1992

Indoor air pollution and pulmonary function in children.

Pulmonary function in winter time in 1,343 school children aged 10-13 years was measured in four cities located in northern and southern part of China. The results showed that FVC, FEV1, PEF, V75, V50 and V25 in children living in homes with coal stoves were decreased by 1.5-10.7% compared with children living in homes with gas or LPG stoves in Chengde and Shanghai. In contrast to this, no significant difference in pulmonary function was found in Shenyang and Wuhan. It suggested that this phenomenon was related to indoor air pollution, and partly related to passive smoking or outdoor air pollution.

Air Pollution, Indoor↗
PubMed1991

Mouse and human retinoic acid receptor beta 2 promoters: sequence comparison and localization of retinoic acid responsiveness.

The retinoic acid receptor beta (RAR beta) gene is a member of the family of retinoic acid/thyroid hormone receptor genes, encoding retinoic acid-inducible transcription factors. To study regulation of the RAR beta gene, genomic clones containing the mouse and human retinoic acid receptor beta 2 (RAR beta 2) promoters were isolated and approximately 1.5 kb of upstream and downstream sequences relative to the transcriptional start site were completely sequenced. Both the mouse and human RAR beta 2 promoters are highly homologous around the transcription initiation site, with perfect conservation of the TATA box and retinoic acid responsive element (RARE). Promoter activation studies in P19 EC cells show, that the RARE in both the human and mouse promoters confers RA-responsiveness to the RAR beta 2 promoter. However, sequences located immediately upstream of the RARE also confer RA-inducibility to both the mouse and human RAR beta 2 gene promoters. This region contains conserved consensus sequences for a TPA-responsive element (TRE) and cAMP-responsive element (CRE), suggesting that in addition to regulation by RA receptors other transcription factors regulate RAR beta 2 expression in EC cells. Furthermore, the availability of the mouse RAR beta 2 promoter should facilitate studies for transgene expression and gene targeting experiments in embryonic stem cells.

Animals↗
PubMed1990

Photon correlation spectroscopy of the polarization signal from single muscle fibres.

Measurements of crossbridge dynamics have been obtained from the spectrum of diffracted light derived from single, skinned fibres of skeletal muscle. This technique combines optical ellipsometry with photon correlation spectroscopy of the intrinsic reporters from the muscle cell. The difference in the intensities of the two linearly polarized electric field components of diffracted light is autocorrelated in time, and the dynamics of optical anisotropy from the contributing units of the sarcomere are measured. In focusing on the fast-time dynamics, we detected two principal features: a rapidly relaxing temporal signal with a relaxation time of approximately 5 microseconds, and an oscillatory component which transforms into a broad but spectrally defined signal centred at around 370 kHz. Experiments were conducted to measure changes of these two signals upon relax-rigor transition and alpha-chymotrypsin degradation. These studies strongly suggest that the relaxational component of the signal is primarily due to myosin crossbridge motion; the 370 kHz spectral signal has as its likely source the myosin thick filament.

Animals↗
PubMed1990

Characteristics of embryonic stem cell differentiation: a comparison with two embryonal carcinoma cell lines.

Embryonic stem (ES) cells isolated from late blastocysts can now be maintained in culture in an undifferentiated state provided they are grown in the presence of a specific differentiation inhibitor, known variously as leukaemia inhibiting factor (LIF) or differentiation inhibiting activity (DIA), found at high concentrations in medium conditioned by Buffalo rat liver (BRL) cells. ES cells acquired a differentiated phenotype in monolayer, either when in the absence of LIF/DIA or in the presence of retinoic acid (RA). We have now characterized this bipotential differentiation of ES cells in terms of a series of extracellular matrix and cell surface proteins as well as cytokeratin expression, and compared it with the changes observed during the differentiation of two embryonal carcinoma (EC) cell lines, P19 and F9. ES cells exposed to RA in the presence of LIF/DIA largely resembled F9 EC + RA after 5 days, while ES cells deprived of LIF/DIA formed a culture with mixed phenotype resembling P19 EC + RA. This study therefore establishes the predominantly parietal endoderm-like phenotype of cells derived from ES by RA induction, and suggests that a mixed population of endoderm- and ill-defined mesoderm-like cells are formed after removal of specific inhibitor(s) of differentiation.

Animals↗
PubMed1989

Lymphocyte subpopulation with low membrane potential in the blood of cyclosporin- and prednisone-treated patients: in vivo selectivity for T4 subset.

Previous work on the mode of action of CsA revealed that this drug shifts the membrane potential of human periferal blood lymphocytes in vitro. Recently we have analyzed lymphocytes of cyclosporin-treated transplant patients. Membrane potential analysis with the DIOC6(3) fluorescence dye indicates that all the studied patients have a subpopulation of lymphocytes with low membrane potential and that this population is made up predominently of OKT4+ cells. However there is no correlation between the clinical events and the percentage distribution of lymphocyte subpopulations as defined by the membrane potential and the T4/T8 ratio of the total lymphocyte population.

CD4-Positive T-Lymphocytes↗
PubMed1989

Polarization states of diffracted light. Changes accompanying fiber activation.

Measurement of the state of optical polarization of light diffracted from single, skinned and intact fibers of anterior tibialis muscle from Rana pipiens revealed a dependence upon rigor, activation, and sarcomere length (SL) change. Changes in total birefringence, delta nT, and differential field ratio value, rT, were determined. In a relaxed, skinned fiber the total birefringence value, delta nT, decreases as sarcomere length is increased from 2.1 microns to approximately 2.8-3.0 microns. From there it increases significantly to a value of approximately 1.8 x 10(-3) at a sarcomere length of 3.6 microns. The differential field ratio, rT, also shows a biphasic response to increasing sarcomere length, first exhibiting a rapid decrease over shorter SL and leveling out after the SL is beyond 3.0 microns. In comparison, relaxed intact fibers change substantially less upon sarcomere length change, showing little change in birefringence and a small bi-phasic change in rT. Skinned fibers were activated using a solution that has the same ionic strength as the relaxing solution and allows repeatable, and sustained activation. A decrease in both delta nT and rT was observed upon fiber activation. The decrease in delta nT and rT was slightly larger at shorter sarcomere lengths than at longer lengths. Relaxed fibers placed in rigor showed changes in delta nT and rT similar to those observed in activated fibers. These results are consistent with the hypothesis that, after activation, a significant portion of the thick filament cross-bridges rotate towards the actin filament resulting in redistribution of the interfilament mass content. They are also consistent with an average orientation of crossbridges in the overlap region different from that in the nonoverlap region.

Animals↗
PubMed1989

Effects of calcium channel blockers on in vivo cellular immunity in mice.

In vitro studies have shown that calcium channel blockers (CCB) inhibit lectin-induced lymphocyte proliferation. However, no in vivo effects have been documented yet. In this study we evaluated the effects of CCB on in vivo cellular immunity by using contact sensitivity to oxazolone in mice. From 15 to 30 twelve-week-old female C3H mice were randomized into: 0.9 NS (sham), ethanol, CsA, dexamethasone (DXM), verapamil, diltiazem, and nifedipine groups. These study agents were given daily from day 1 to day 9 subcutaneously to the shaved abdominal wall. The mice were sensitized with oxazolone to the abdominal wall on day 2 and challenged with oxazolone on the right ear on day 8. Delayed-type hypersensitivity was measured on day 10 and defined as the difference in thickness between the right (challenged) and left (control) ear of each mouse. The mean DTH of each study group was compared with that of the sham, and the statistical significance was determined by a Student's t test. The percentage of change in DTH from the sham was also calculated as: (mean DTH of study drug group-mean DTH of sham group)/mean DTH of sham group x 100%. A negative value meant a suppressive effect on DTH; a positive value, an enhancing one. The CsA, DXM, and nifedipine all had significant suppressive effects on DTH. Verapamil had a significant enhancing effect. Ethanol and diltiazem had no significant effect. More studies employing other antigens with several other cell-mediated response measurements along with DTH quantification should be done in order to determine the specificity of the immunosuppressive effect of CCB as well as the potential of any calcium antagonist as an adjuvant suppressive agent.

Animals↗
PubMed1989

[The role of medial medulla in the depressive responses in pulmonary and carotid arteries to injection of acetylcholine at fourth ventricle].

The role of medial medulla in the depressive responses in pulmonary and carotid arteries to injection of acetylcholine (ACh) at the fourth ventricle was studied by means of electrolytic destruction and microinjection of drugs at the relevant brain areas. It was found that (1) electrolytic destruction of medial medulla significantly diminished the depressive responses to ACh in pulmonary and carotid arteries; (2) destruction of nucleus tractus solitarius (NTS) at the level of the medullary obex did not affect the depressive responses in both arteries; obex did not affect the depressive responses in both arteries; (3) microinjection of 5-hydroxytryptamine (5-HT) blockers, cyproheptadine and 2-bromolysergic acid diethylamide (BOL), into the fourth ventricle or medial medulla could lessen the depressive responses to ACh in pulmonary and carotid arteries; (4) microinjection of naloxone in the same way could partially abolish the depressive responses. It is thus assumed that the ACh-induced depressive responses in pulmonary and carotid arteries are associated with the structural integrity of the medial medulla but not related to the central projection area of the buffer nerves. Therefore, the depressive responses in pulmonary and carotid arteries initiated by injection of ACh at the fourth ventrical are mediated by activating the 5-HT and endorphin systems of the medial medulla which in turn inhibits the tonic activities of the sympathetic preganglionic neurons in the spinal cord.

Acetylcholine↗
PubMed1988

Incidence and morbidity of cytomegalovirus disease associated with a seronegative recipient receiving seropositive donor-specific transfusion and living-related donor transplantation. A multicenter evaluation.

This retrospective study was conducted to identify the frequency of cytomegalovirus (CMV) disease in seronegative recipients of donor-specific transfusion (DST) and living-related donor (LRD) kidneys from seropositive donors. A total of 151 LRD transplants (TX) were performed at six transplant centers over a 3-year period. A total of 33 patients were identified as having been seronegative (pre-TX) for CMV, yet they had DST and a TX from a seropositive LRD. Of these patients, 12 (36.4%) seroconverted within the first 6 months post-TX and developed clinical CMV disease. Additional patients seroconverted, but did not have evidence of clinical disease and were not tested further. All TX centers, with the exception of one, had seronegative patients that became ill after receiving a seropositive DST/LRD TX. Six patients manifested their disease as a febrile illness with leukopenia and liver enzyme elevations, four had pneumonitis, and two developed CMV ulcerations of the colon (one of whom died from resultant sepsis). Of the 36 seronegative patients who received seronegative DST/LRD TX none became ill with CMV disease. Of the 72 seropositive patients who received DST/LRD TX, only 2 (2.8%) developed CMV illness (one, seropositive into seropositive, the other, seronegative into seropositive). Of the 33 seronegative patients receiving seropositive DST/LRD TX, 17 received antilymphocyte preparations (ALP), and 8 of these became ill (47.1%). Of 16 patients not receiving ALP, 5 (31.3%) developed clinical CMV illness. Of the 33 patients who were identified as having been seronegative for CMV yet received seropositive DST/LRD TX, the 12 who did develop CMV illness had two graft losses, one death, and a serum creatinine for the remaining 9 patients of 2.3 +/- 1.6 at last follow-up. The remaining 21 patients who developed no illness had a serum creatinine of 1.3 +/- 0.6 with no graft losses at the last follow-up. This evidence suggests that a prospective TX recipient who is seronegative for CMV who receives DST/LRD TX from a seropositive family member has a significant risk for developing morbidity related to clinical CMV illness.

Adolescent↗
PubMed1985

Translation of type IV procollagen messenger RNA from cultured cat retinal pigment epithelial cells.

The activity of type IV procollagen mRNA was detected in the total cytoplasmic RNA prepared from normal feline retinal pigment epithelial cells in culture. The translation products contained two distinct bands in the pro alpha chain region on SDS-PAGE, which were sensitive to collagenase digestion. Corresponding bands were identified in the immunoprecipitate of the translation products after reaction with an anti-type IV collagen antiserum and separation by protein A-Sepharose column chromatography.

Animals↗