Search PubMed⌕ Search

Biomedical subjects

M Chen

Publications and source records attributed to M Chen.

At least 739 records · Page 41Linked to original sources
PubMed1993

[Pathology of muscle contracture caused by injection and activity of phosphochesterase and insulin receptor].

The animal model of muscle contracture caused by injection was set up in the experiment. We used the model for excessive healing studies and researched the changes in its pathology, and activity of phosphochesterase and insulin receptor in this model. The experimental results revealed that the pathologic changes belonged to excessive proliferation of connective tissue (excessive healing). When occurred muscle degeneration, infiltration of inflammatory cells, proliferation of fibroblasts and descending of collagen fibers, the activity level phosphochesterase and insulin receptor became higher. The excessive healing occurrence may have something to do with the changes of phosphochesterase and insulin receptor.

5'-Nucleotidase↗
PubMed1993

Changes of calmodulin contents in single vascular smooth muscle cells from the tail arteries of spontaneously hypertensive rats.

By combining immunohistochemistry and fluorocytometry techniques, total calmodulin (total CaM), Ca(2+)-bound calmodulin (Ca.CaM) and total protein contents in single vascular smooth muscle cells (VSMC) enzymatically dispersed from the tail arteries of young (5-7 weeks old, prehypertensive) and adult (20-24 weeks old, established hypertensive) stroke-prone spontaneously hypertensive rats (SHRsp) were studied and compared with those of age-matched Wistar-Kyoto rats (WKY). No significant difference was found in total CaM, Ca.CaM and protein contents between young SHRsp and WKY. Total CaM and protein contents in adult SHRsp were increased by similar degrees (30.7% and 27.5%, respectively) as in age-matched WKY, suggesting that increased total CaM content may be a consequence of increased synthesis of cellular protein during hypertension. However, Ca.CaM contents in adult SHRsp were significantly increased over those in age-matched WKY by a much higher degree (86.2%), reflecting an abnormal Ca2+ homeostasis in single VSMCs during hypertension.

Age Factors↗
PubMed1993

Ontogeny of corneal epithelial tight junctions: stratal locale of biosynthetic activities.

PURPOSE: On reaching the surface position, corneal epithelial cells assemble a tight paracellular barrier rapidly. The purpose of this study was to identify at what maturation stage the cells acquire biochemical elements underpinning this ability. METHODS: Rabbit corneas were subjected to a digitonin-exposure protocol that results in the devitalization and desquamation of the three outermost cell layers of the 5-6-layer thick epithelium and thus, exposes winglike cells to the tear surface. Corneas were then mounted in Ussing-type chambers to measure transepithelial resistance and solute fluxes. RESULTS: After the devitalization treatment transepithelial resistance remained near baseline for 2 hours and then rose to 8.24 +/- 3.12 K omega.cm2 (+/- SD, n = 15) during the next 8 hours. This increase was matched by increases in the resistance to the paracellular flow of mannitol. Transmission electron microscopy confirmed de novo formation of tight junctions over this time span in the new surface. The addition of transcription (actinomycin D; alpha-amanitin), translation (cycloheximide), core glycosylation (tunicamycin), and endoplasmic reticulum-to-Golgi traffic (brefeldin A) inhibitors immediately after the devitalization protocol prevented the transepithelial resistance raise. Introducing time delays between the cell devitalization and the addition of these biosynthesis inhibitors reduced their effect; a time delay of 90 minutes abolished the inhibition by alpha-amanitin. CONCLUSION: Devitalization of overlying cells induces the assembly of a tight paracellular barrier in the wing cells. The process requires and includes the synthesis of essential transcripts and proteins that were initially absent in these cells. In vivo, the synthesis of these elements must occur as cells reach the squamous stage of maturation.

Amanitins↗
PubMed1992

Studies of the cloned 37-kDa subunit of activator 1 (replication factor C) of HeLa cells.

The elongation of primed DNA templates by DNA polymerase delta and DNA polymerase epsilon requires the action of two accessory proteins, proliferating cell nuclear antigen and activator 1 (A1, also called replication factor C). A1 is an enzyme that contains five different subunits (145, 40, 38, 37, and 36.5 kDa). In this paper, we describe the isolation of the gene encoding the 37-kDa subunit from HeLa cells. This gene was cloned, sequenced, and overexpressed in Escherichia coli. The amino acid sequence shows a high degree of homology to the 40-kDa subunit of A1; they both contain the identical ATP-binding motif, but in contrast to the bacterial expressed 40-kDa protein, the 37-kDa expressed protein did not bind ATP. Both the 37- and 40-kDa proteins share substantial homology with the phage T4 gene 44 protein and to a lesser extent with the tau and gamma subunits of the E. coli DNA polymerase III holoenzyme. Polyclonal antibodies against the bacterially expressed 37- and 40-kDa proteins do not crossreact and are specific in their interaction. Antibodies against the 37-kDa protein maximally inhibited (by 50%) the A1-dependent synthesis of DNA by DNA polymerase delta; antibodies against the 40-kDa protein quantitatively inhibited the same reaction. When A1-dependent synthesis of DNA was partially inhibited by antibodies against the 40-kDa subunit, the addition of antibodies against the 37-kDa subunit inhibited DNA synthesis to a greater extent than the anti-37-kDa antibody alone. These results suggest that both the 37- and 40-kDa subunits of A1 are required for the biological role of A1 and that they may function differently in this process.

Amino Acid Sequence↗
PubMed1992

A mutant of TTX-resistant cardiac sodium channels with TTX-sensitive properties.

The cardiac sodium channel alpha subunit (RHI) is less sensitive to tetrodotoxin (TTX) and saxitoxin (STX) and more sensitive to cadmium than brain and skeletal muscle (microliter) isoforms. An RHI mutant, with Tyr substituted for Cys at position 374 (as in microliter) confers three properties of TTX-sensitive channels: (i) greater sensitivity to TTX (730-fold); (ii) lower sensitivity to cadmium (28-fold); and (iii) altered additional block by toxin upon repetitive stimulation. Thus, the primary determinant of high-affinity TTX-STX binding is a critical aromatic residue at position 374, and the interaction may take place possibly through an ionized hydrogen bond. This finding requires revision of the sodium channel pore structure that has been previously suggested by homology with the potassium channel.

Amino Acid Sequence↗
PubMed1992

Modular expression and secretion vectors for Bacillus subtilis.

A modular vector system has been developed for the extracellular production of heterologous proteins in Bacillus subtilis. This modular vector system consists of four secretion vectors which are based upon the genes encoding the Bacillus amyloliquefaciens extracellular alkaline protease, neutral protease, barnase and levansucrase. The modular vectors contain compatible restriction sites downstream from the signal peptide-coding region. Three reporter proteins (staphylococcal protein A, levansucrase and Escherichia coli alkaline phosphatase) that offer complementary advantages for cloning, genetic manipulations and media optimization have been fused to the various signal peptides. These secretion vectors function in E. coli and hence can be used to compare the mechanisms of protein secretion in E. coli and B. subtilis.

Alkaline Phosphatase↗
PubMed1992

Serotonin-mediated endocytosis of apCAM: an early step of learning-related synaptic growth in Aplysia.

The long-term facilitation of synaptic efficacy that is induced by serotonin in dissociated cell cultures of sensory and motor neurons of Aplysia is accompanied by the growth of new synaptic connections. This growth is associated with a down-regulation in the sensory neuron of Aplysia cell adhesion molecules (apCAMs). To examine the mechanisms of this down-regulation, thin-section electron microscopy was combined with immunolabeling by gold-conjugated monoclonal antibodies specific to apCAM. Within 1 hour, serotonin led to a 50% decrease in the density of gold-labeled complexes at the surface membrane of the sensory neuron. This down-regulation was achieved by a heterologous, protein synthesis-dependent activation of the endosomal pathway, which leads to internalization and apparent degradation of apCAM. The internalization is particularly prominent at sites where the processes of the sensory neurons contact one another and may act there to destabilize process-to-process contacts that normally inhibit growth. In turn, the endocytic activation may lead to a redistribution of membrane components to sites where new synapses form.

Animals↗
PubMed1992

Sequence and expression in Escherichia coli of the 40-kDa subunit of activator 1 (replication factor C) of HeLa cells.

Activator 1 (A1; also called replication factor C), in conjunction with proliferating-cell nuclear antigen (PCNA), is essential for the elongation of primed DNA templates by DNA polymerases delta and epsilon. A1 contains five distinct subunits of 145, 40, 38, 37, and 36.5 kDa. Here we describe the isolation, sequence, and bacterial expression of a cDNA coding for the 40-kDa subunit. In keeping with the presence of an ATP-binding motif, the bacterially expressed 40-kDa subunit binds ATP. The interaction between the 40-kDa subunit and ATP was reduced by the addition of PCNA. In addition, antibodies raised against the 40-kDa subunit abolished the A1- and PCNA-dependent synthesis of DNA catalyzed by polymerase delta. The putative amino acid sequence of the 40-kDa subunit of A1 revealed significantly homology with the bacteriophage T4 gene 44 protein and, to a lesser degree, with the tau and gamma subunits of Escherichia coli DNA polymerase III holoenzyme.

Adenosine Triphosphate↗
PubMed1992

Mortality and incidence of bladder cancer in benzidine-exposed workers in China.

We examined bladder cancer mortality and incidence to 1981 in 1,972 workers employed in benzidine-exposed jobs in Tianjin, Shanghai, and Jilin, China, between 1972 and 1977, and in 1,974 unexposed workers employed during the same time period. In comparison to general population rates, in the benzidine-exposed group the ratio of observed to expected deaths (SMR) was 17.5 (95% C.I.: 7.5-34.5) and the ratio of observed to expected incident cases (SIR) was 25.0 (95% C.I.: 16.9-35.7). No excess was noted in the unexposed group. The 25-fold increase in bladder cancer incidence in the exposed group was related to level of exposure, with the SIR rising from 4.8 for low exposure to 36.2 for medium exposure, and 158.4 for high exposure. Risks were elevated both for producers of benzidine (SIR = 45.7; 95% C.I.: 20.9-86.8) and for users (SIR = 20.9; 95% C.I.: 12.9-32.0) of benzidine dyes. Benzidine-exposed workers who smoked tobacco had a 31-fold risk (95% C.I.: 20.4-46.4), while non-smoking workers had an 11-fold risk (95% C.I.: 3.6-25.8), suggestive of a multiplicative relationship between these two carcinogens.

Air Pollutants, Occupational↗
PubMed1992

HLA-DRB3 gene alleles in Caucasian patients with Graves' disease.

Graves' disease (GD) is a human leukocyte antigen (HLA) linked organ-specific autoimmune disease. In German GD patients the disease is associated with HLA specificities of the HLA-DRw52 family (HLA-DR3, -DR5, and DR6; HLA-DRB3 positive HLA haplotypes). Recently, a strong association with a HLA-DRB3 restriction fragment length polymorphism gene has been described. To study HLA-DRB3 alleles and their association with the disease, a large cohort of controls (n = 3724) and GD patients (n = 304) was analyzed. HLA-DR allelic combinations revealed an increase in HLA-DR3/DR5 heterozygous patients (relative risk 2.9; P < 0.001). HLA-DRB3 alleles, as defined by DNA typing in HLA-DR matched groups revealed a significant increase in DRB3*0101 homozygosity (relative risk 17.5; P < 0.001) in HLA-DR3 homozygous patients. In GD patients with ophthalmopathy (grade II or higher, according to Werner) DRB3*0101/*0202 heterozygosity revealed an increased relative risk of 5.5 (P < 0.001). Non-HLA-DR3 homozygous, DRB3*0101/*0202 heterozygous patients were at the highest risk for endocrine ophthalmopathy (relative risk 10; P < 0.001). Our data, based on DNA typing methods of HLA-D genes, provide evidence that the susceptibility is strongly associated with HLA-DRB3 genes.

Alleles↗
PubMed1992

The cloned cardiac Na channel alpha-subunit expressed in Xenopus oocytes show gating and blocking properties of native channels.

The neonatal rat cardiac Na channel alpha-subunit directed currents in oocytes show characteristic cardiac relative resistance to tetrodotoxin (TTX) block. TTX-sensitive currents obtained by expression in Xenopus oocytes of the alpha-subunits of the rat brain (BrnIIa) and adult skeletal muscle (microI) Na channels show abnormally slow decay kinetics. In order to determine if currents directed by the cardiac alpha-subunit (RHI) exhibit kinetics in oocytes like native currents, we compared RHI-directed currents in oocytes to Na currents in freshly isolated neonatal rat myocytes. The decay rate of RHI currents approached that of neonatal myocytes and was faster than BrnIIa and microI currents in oocytes. The voltage dependence of availability and activation was the same as that in the rat myocytes except for a 12-19 mV shift in the depolarizing direction. The RHI Na currents were sensitive to Cd2+ block, and they showed use dependence of TTX and lidocaine block similar to native currents. The current expressed in oocytes following injection of the cRNA encoding for the alpha-subunit of the cardiac Na channel possesses most of the characteristic kinetic and pharmacological properties of the native cardiac Na current.

Animals↗
PubMed1992

Binocularity and excitability loss in visual cortex cells of corpus callosum transected kittens and cats.

The contribution of the corpus callosum to binocularity of visual cortex cells and to their responsiveness was studied in cats. Electrophysiological recordings of the responses of single cells to visual stimulation was performed in the callosal projection zone, visual cortex area 17-18 boundary in callosotomized cats. Callosotomy was carried out by transection of the visual segment of the corpus callosum in 6-7-week-old kittens and in acute and chronic adult cats (postoperative recovery time: 11 days-39 months). While in our normal cats the common proportion of binocularly driven cells (79.8%) was found (66.3% in the sham controls), a remarkable diminution (29.7%) was found in the callosotomized kittens, in the acute (39.7%) and in the chronic (50.6%)-operated cats. We have also found a change in the amount of binocularity as function of postoperative recovery time. While the proportion of binocular cells was conceivable (60.7%) in the short- and intermediate-term callosotomized cats (postoperative time: 0.3-5.5 months), it was diminished (36.9%) in the long-term (6.5-39 months) chronic cats. As to the responsiveness level, it was found that visual responsive cells constituted 88% of the cells in the normal and 80.3% in the sham controls. In comparison, they constituted 69.2% in the acute, 54.4% in the chronic and 52.8% in the callosotomized kittens. Furthermore, callosal transection had produced a symmetric effect in the two hemispheres, regarding binocularity and responsiveness. It has been thus concluded that the corpus callosum is essential for the mediation of binocular functions between the two hemispheres; in addition, cortical excitability has been also found to depend on callosal integrity.

Animals↗
PubMed1992

Inhibitors of protein and RNA synthesis block structural changes that accompany long-term heterosynaptic plasticity in Aplysia.

Synaptic connections between the sensory and motor neurons of Aplysia in culture undergo long-term facilitation in response to serotonin (5-HT) and long-term depression in response to FMRFamide. These long-term functional changes are dependent on the synthesis of macromolecules during the period in which the transmitter is applied and are accompanied by structural changes. There is an increase and a decrease, respectively, in the number of sensory neuron varicosities in response to 5-HT and FMRFamide. To determine whether macromolecular synthesis is also required for the structural changes, we examined in parallel the effects of inhibitors of protein (anisomycin) or RNA (actinomycin D) synthesis on the structural and functional changes. We have found that anisomycin and actinomycin D block both the enduring alterations in varicosity number and the long-lasting changes in synaptic potential. These results indicate that macromolecular synthesis is required for expression of the long-lasting structural changes in the sensory cells and that this synthesis is correlated with the long-term functional modulation of sensorimotor synapses.

Animals↗