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Biomedical subjects

Q Chen

Publications and source records attributed to Q Chen.

At least 703 records · Page 39Linked to original sources
PubMed1992

Domains of type X collagen: alteration of cartilage matrix by fibril association and proteoglycan accumulation.

During endochondral bone formation, hypertrophic cartilage is replaced by bone or by a marrow cavity. The matrix of hypertrophic cartilage contains at least one tissue-specific component, type X collagen. Structurally type X collagen contains both a collagenous domain and a COOH-terminal non-collagenous one. However, the function(s) of this molecule have remained largely speculative. To examine the behavior and functions of type X collagen within hypertrophic cartilage, we (Chen, Q., E. Gibney, J. M. Fitch, C. Linsenmayer, T. M. Schmid, and T. F. Linsenmayer. 1990. Proc. Natl. Acad. Sci. USA. 87:8046-8050) recently devised an in vitro system in which exogenous type X collagen rapidly (15 min to several hours) moves into non-hypertrophic cartilage. There the molecule becomes associated with preexisting cartilage collagen fibrils. In the present investigation, we find that the isolated collagenous domain of type X collagen is sufficient for its association with fibrils. Furthermore, when non-hypertrophic cartilage is incubated for a longer time (overnight) with "intact" type X collagen, the molecule is found both in the matrix and inside of the chondrocytes. The properties of the matrix of such type X collagen-infiltrated cartilage become altered. Such changes include: (a) antigenic masking of type X collagen by proteoglycans; (b) loss of the permissiveness for further infiltration by type X collagen; and (c) enhanced accumulation of proteoglycans. Some of these changes are dependent on the presence of the COOH-terminal non-collagenous domain of the molecule. In fact, the isolated collagenous domain of type X collagen appears to exert an opposite effect on proteoglycan accumulation, producing a net decrease in their accumulation, particularly of the light form(s) of proteoglycans. Certain of these matrix alterations are similar to ones that have been observed to occur in vivo. This suggests that within hypertrophic cartilage type X collagen has regulatory as well as structural functions, and that these functions are achieved specifically by its two different domains.

Animals↗
PubMed1992

Effects of light beam size on fluence distribution and depth of necrosis in superficially applied photodynamic therapy of normal rat brain.

The light fluence distributions of 632.8 nm light incident on the exposed surface of normal rat brain in vivo have been measured using an interstitial, stereotactically-mounted optical fiber detector with isotropic response. The dependence of the relative fluence rate on depth and the spatial distribution of fluence were compared for incident beam diameters of 3 and 5 mm. The fluence rate at depth of 1-6 mm along the optical axis within the brain tissue was approximately 70% greater for a 5 mm diameter beam than for a 3 mm beam, at the same incident fluence rate, although the plots of the relative fluence rate vs depth were parallel over the depth range 1-6 mm. The depths of necrosis resulting from photodynamic treatment of brain tissue using the photosensitizer Photofrin and irradiation by 632 nm light with 3 and 5 mm incident beams were also measured. The observed difference in necrosis depths was consistent with the measured difference in fluence. The importance of beam size in photodynamic treatment with small diameter incident light fields is discussed.

Animals↗
PubMed1992

The superficial buffer barrier in vascular smooth muscle.

Force development and fura-2 fluorescence were simultaneously measured in the rabbit inferior vena cava. Discharging SR Ca2+ with either caffeine or norepinephrine prior to stimulation of Ca2+ influx induced a delay of 30-70 s between the intracellular Ca2+ signal and development of force. This delay was abolished by the application of caffeine. These data support the superficial buffer barrier hypothesis, which holds that Ca2+ entry from the extracellular space proceeds via a restricted cytoplasmic region between the inner plasmalemmal surface and the peripheral sarcoplasmic reticulum (SR). Ca2+ accumulation by this SR fraction appears to be able to delay Ca2+ entry into the deeper myoplasm where it activates the myofilaments. Caffeine and thapsigargin elevated the steady-state [Ca2+]i, suggesting a contribution by the SR Ca2+ pump to Ca2+ extrusion from the cells. Norepinephrine enhanced myofilament Ca2+ sensitivity, while caffeine decreased it.

Animals↗
PubMed1992

Expression and transport of rabbit surfactant protein A in COS-1 cells.

SV40-transformed green monkey kidney (COS-1) cells were transfected with expression plasmids that contained either the structural gene or cDNA for surfactant protein A (SP-A), a major protein of rabbit lung surfactant. The transfected COS-1 cells synthesized several isoforms of SP-A that were found to be less acidic than those produced in rabbit lung tissue. SP-A species with apparent molecular weight (M(r)) approximately equal to 29,000-33,000 were detected in the transfected cells, whereas glycosylated forms with apparent M(r) approximately equal to 33,000-38,000 were detectable only in the culture medium. Analysis of transfected cells by indirect immunofluorescence revealed that SP-A was localized in punctate bodies throughout the cytoplasm. Expressed SP-A was not detectable on the cell surface nor was there evidence that secreted SP-A was endocytosed by COS-1 cells. After subcellular fractionation of the transfected COS-1 cells, SP-A was found to be localized predominantly in the 5,000- and 18,000-g pellet fractions; little or no immunoreactive SP-A was detectable in cytosolic fractions. Treatment of transfected cells with the glycosylation inhibitor tunicamycin prevented secretion of SP-A into the medium, suggesting a role of glycosylation in secretion of SP-A. On the other hand, treatment of transfected cells with inhibitors of proline hydroxylation, which may cause destabilization of the collagen-like domain of SP-A, reduced but did not prevent secretion of SP-A into the culture medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Rabbit lung surfactant protein A gene: identification of a lung-specific DNase I hypersensitive site.

Expression of the gene encoding pulmonary surfactant protein A, SP-A, is lung specific and developmentally and hormonally regulated. Previously, we observed that SP-A gene transcription is initiated in fetal rabbit lung after day 21 of gestation and reaches maximal levels by day 28. In the present study, a cDNA specific for rabbit SP-A was used to isolate the SP-A gene from a rabbit genomic library. A 7.6-kb fragment containing the entire structural gene and approximately 380 bp of 5'-flanking DNA was isolated and characterized. The transcription initiation site, mapped by primer extension analysis, was localized 23 bp downstream of a putative TATA element. The structural gene is composed of five exons and four introns. The first exon encodes the 5'-untranslated region of the mRNA; the translation initiation site is in exon II, and exon V contains the two polyadenylation sites that give rise to the 2.0- and 3.0-kb species of SP-A mRNA. A potential adenosine 3',5'-cyclic monophosphate (cAMP)-regulatory element (CRE) was identified at -261 bp, and sequences with homology to glucocorticoid-regulatory element (GRE) half-sites were found at -150 and -190 bp upstream of the transcription initiation site and within the first intron. A DNase I hypersensitive site was identified in genomic DNA isolated from 21- and 28-day fetal and adult rabbit lung tissues. This site was mapped within the 5'-flanking region of the SP-A gene, at approximately -80 to -180 bp upstream of the transcription initiation site. The absence of this hypersensitive site in genomic DNA of liver, kidney, and heart tissues suggests that altered chromatin structure may serve a role in lung-specific SP-A gene expression. The presence of this tissue-specific DNase I hypersensitive site in lung nuclei from 21-day gestational age fetal rabbits suggests that the SP-A gene may exist in an accessible conformation prior to the time of transcription initiation.

Amino Acid Sequence↗
PubMed1992

Transferrin subtypes in 11 south China minority populations.

Transferrin subtypes were determined by isoelectric focussing (IEF) in a total of 2,121 individuals from 11 South China minority populations. The C1, C2 and DCHI alleles were present in all the populations; B alleles were lacking, C4 was found in 3 populations and C3 in 6. C2 and C4 allele frequencies are notable in these minority groups. The frequency of the C2 allele was higher (0.25-0.38) than that of Han Chinese (0.18-0.25). In Bai the C2 frequency was as high as 0.38. The C4 allele was present at a low frequency (less than 0.01), which suggests that this allele probably existed in the ancestral Mongoloid population at a low frequency and increased in frequency in Amerindians due to genetic drift or other factors.

Alleles↗
PubMed1992

Magnetoencephalography of focal cerebral ischemia in rats.

BACKGROUND AND PURPOSE: The purpose of this study was to use magnetoencephalography to record magnetic field changes in the brain during middle cerebral artery occlusion. METHODS: A direct-current electrocorticogram (two channels) and a direct-current magnetoencephalogram (seven channels) were simultaneously recorded from five rats subjected to middle cerebral artery occlusion for 1-2 hours. RESULTS: Direct-current electrocorticographic and direct-current magnetoencephalographic signal deflections were observed after the onset of middle cerebral artery occlusion and occurred repeatedly throughout the ischemic period, with a mean +/- SD time interval of 12 +/- 5 minutes. A one-to-one correspondence of the electrocorticographic and magnetoencephalographic signal deflections was demonstrated. CONCLUSIONS: Direct-current magnetoencephalography can provide a new noninvasive technique for studying depolarization and/or spreading depression in focal cerebral ischemia.

Animals↗
PubMed1992

Induction of acetylcholine receptor clustering by native polystyrene beads. Implication of an endogenous muscle-derived signalling system.

Aneural muscle cells in culture often form acetylcholine receptor (AChR) clusters, termed hot spots, which are similar to those found at the postsynaptic membrane both in structure and in molecular composition. Although hot spots form on both dorsal and ventral surfaces of the cell, the ventral ones are better characterized because of their association with sites of cell-substratum contact. To understand the stimuli and mechanisms involved in ventral hot spot formation, native, uncoated polystyrene beads were applied to cultured Xenopus myotomal muscle cells to create local membrane-substratum contacts. These beads were able to induce a postsynaptic-type development as evidenced by the clustering of AChRs and the development of a set of ultrastructural specializations, including membrane infoldings and a basement membrane. Whereas these native beads were effective in inducing clustering, beads coated with bovine serum albumin or treated with serum-containing medium were ineffective. Native beads were also capable of inducing clusters in serum-free medium, indicating that their effect was mediated by endogenous molecules that were locally presented by the beads, rather than by bead adsorption of components in the medium. Heparan sulfate proteoglycan (HSPG) is a major component of the muscle extracellular matrix and our previous study has shown that basic fibroblast growth factor (bFGF), a member of the heparin-binding growth factor (HBGF) family, and its receptor are present in Xenopus myotomal muscle during the period of synaptogenesis. Therefore, we tested the involvement of HBGF in bead induction. The results of this study show the following: (1) preincubation of cultures in heparin, which solubilizes matrix-bound HBGFs, suppressed the bead-induced AChR clustering. (2) Suramin, which interferes with the interaction between several growth factors and their receptors, also inhibited bead-induced clustering. (3) Tyrphostin, which blocks tyrosine kinase activity associated with a number of growth factor receptors, was also inhibitory to the bead effect. (4) The percentage of bead-induced AChR clusters was significantly enhanced by pretreating the cultures with bFGF prior to bead application. This exogenously applied bFGF could be largely removed by treatment of cultures with heparin, suggesting its association with HSPG at the cell surface. (5) An anti-bFGF neutralizing antiserum significantly reduced the efficacy of the bead stimulation. These data suggest that uncoated beads, which adhere to the cell surface and can mimic the cell-substratum interaction, effect a local presentation of HBGFs, such as bFGF, residing with the HSPG to their membrane receptors, thereby locally activating receptor-associated tyrosine kinases.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Induction of dystrophin localization in cultured Xenopus muscle cells by latex beads.

The distribution of dystrophin in Xenopus myotomal muscle cells was examined in conventional and confocal immunofluorescence microscopy. By labeling dissociated single muscle fibers with a monoclonal or a polyclonal antibody against dystrophin, we found that dystrophin is ten times more concentrated at the myotendinous junction (MTJ) than at the extrajunctional sarcolemma. At the MTJ, dystrophin lines the membrane invaginations where myofibrils attach to the membrane. It is colocalized with talin, but is not related to the distribution of acetylcholine receptors (AChRs) which are clustered at the postsynaptic membrane in the vicinity of the MTJ in these fibers. We found that the localization of dystrophin can be induced in cultured Xenopus myotomal muscle cells by treating them with polystyrene latex beads. Dystrophin is discretely localized at the bead-muscle contacts. With electron microscopy, a sarcolemma specialization with all the salient features of the MTJ, including basal lamina-lined membrane invaginations along which myofibrils make attachment. Although these beads also induce clustering of AChRs, the patterns of dystrophin and AChR localization are distinct. The appearance of dystrophin at the bead-contacted sarcolemma is coincident with the development of the membrane invaginations. This, together with its concentration along membrane invaginations at the MTJ in vivo, suggests a role for dystrophin in the formation of this junctional specialization. Since the signal for MTJ development can be presented to cultured muscle cells in a temporally and spatially controlled manner by beads, this system offers a simple model for analyzing the mechanism of this sarcolemma specialization.

Animals↗
PubMed1992

The effect of light fluence rate in photodynamic therapy of normal rat brain.

This paper reports the effect of incident light fluence rate on the depth to which necrotic lesions are produced by photodynamic therapy (PDT) in the brains of normal Fisher rats. The rats were injected intraperitoneally with Photofrin (12.5 mg kg-1) 48 h prior to PDT with a fixed incident fluence of 35 J cm-2. The treatment was performed at 10, 50, 100, and 200 mW cm-2 and also in a periodic manner (30 s "on" at 100 mW cm-2, 30 s "off"). The depth to which necrosis occurred was determined 24 h after treatment by microscopic examination of tissue sections. No differences were found in the depth to which necrosis was produced by any of the five irradiation schedules. This finding is discussed in the context of other published dose-rate experiments.

Animals↗
PubMed1992

[Effects of calcium channel blocker verapamil on hippocampal kindled seizures induced by coriaria lactone in rabbits].

Eighteen fully kindled rabbits, whose epilepsy had been produced by intrahippocampal (i.h.) injections of 2 microliters of diluted solution containing 0.32 or 0.55 micrograms of coriaria lactone (CL), were separated into three groups. One of them was used as the control group. For seizure, all animals were given CL (0.6-1 micrograms/2 microliter i.h.). Ten minutes later, the verapamil (VR) group of six rabbits was treated with VR (1.5 or 2 mg/kg i.m. 2.5 or 5 micrograms/2 microliters i.h.); the normal saline (NS) group (six rabbits) received 0.8 ml/kg (i.m., in the same volume as that of the VR 2 mg/kg injection) or 2 microliters (i.h.) of NS; the control group of six received neither VR nor NS. The experiments were made once every eight days. Hippocampal EEGs of all animals were recorded by telemetric method and their behavior after injection was observed continuously in 4-7 hours. The results of the experiment indicated that the i.h. administration of 2.5 or 5 micrograms/2 microliters of VR is effective on hippocampal kindled seizures induced by CL in rabbits, but the curative effects of the i.m. administration of 1.5 or 2 mg/kg of VR were less notable than those of the i.h. administration.

Animals↗
PubMed1992

[Lead concentrations in urine correlated with cytogenetic damages in workers exposed to lead].

The lead concentrations in urine and the frequency of chromosomal aberrations and sister chromatid exchanges in lymphocytes of 84 printers exposed to lead were investigated. The results demonstrated that the lead concentrations in urine of printers were higher than normal subjects. The frequency of chromosomal aberrations and sister chromatid exchanges increased significantly with the rise of lead concentrations in urine, showing a linear correlation. The regression equations were Y = 1.31 + 9.07 X and Y = 4.24 + 14.91 X respectively. Therefore, the genetic condition of workers who have high lead concentrations in urine should be attended to and appropriate protective measures should be under-taken.

Adult↗
PubMed1992

[A preliminary study of the chord and specific time constants in 342 healthy children].

Using Knudson's method, the chord time constant, tau ch, tau ch75, tau ch50, tau ch25, and specific time constant, S tau, 1/V75, 1/V50, 1/V25, at high, middle and low lung volumes were calculated from V75, V50 and V25 of the MEFV curves measured previously from 342 healthy children of 3-6 years of age in a nursery. The multiple stepwise regression equation were built with age, height and FVC as independent variables by the IBM-XT/PC computer. The result showed that the S tau corrected by volume from tau ch could reflect the time required for change of unit lung volume more precisely than tau ch owing to the elimination of the influence of lung volume. The S tau was shortened with the increase of age, and was negatively correlate with age and FVC. These facts reflected the growth of lung elastic pressure (PLel) and airway conductance (Gaw) with the increase of age. The prolongation of S tau with the decay of lung volume just reflected the decrease of PLel and Gaw with the decay of lung volume. No regular changes of tau h were observed with age and lung volume. Probably, it was concerned with the complexity of factors affecting the tau ch.

Airway Resistance↗
PubMed1992

[Chemical studies on immunologically active polysaccharides of Ganoderma lucidum(Leyss. ex Fr.) Karst].

BN3B, the polysaccharide component of the fruit of Ganoderma lucidum, has been shown to have immune activity. From BN3B four homogeneous polysaccharides were separated and purified. Chemical studies on the main components BN3B1 and BN3B3 indicated that BM3B1 contained only glucose and should be a glucan containing beta-(1----6) and (1----3)glycoside bonds and that BN3B3 was an arabinogalactan containing beta-(1----6) and (1----3)glycoside bonds.

Adjuvants, Immunologic↗