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Biomedical subjects

L Chen

Publications and source records attributed to L Chen.

At least 1,315 records · Page 73Linked to original sources
PubMed1992

Cloning of the alpha 1 subunit of a voltage-dependent calcium channel expressed in pancreatic beta cells.

The isoforms of the alpha 1 subunits of voltage-dependent Ca2+ channels expressed in human pancreatic islets were identified by using a pair of degenerate oligonucleotide primers and the polymerase chain reaction (PCR) to amplify mRNAs encoding alpha 1 subunit-like sequences. The sequences of the PCR products indicate that islets express the heart-type alpha 1 subunit as well as a second isoform whose complete sequence has not been previously reported. The sequences of cloned cDNAs encoding the human beta-cell, or neuroendocrine-type, alpha 1 subunit indicate that it is composed of 2181 amino acids. It shares 68%, 64%, and 41% identity with the sequences of the alpha 1 subunits of rabbit heart, skeletal muscle, and brain, respectively, and is predicted to have a similar structure including four homologous domains composed of six membrane-spanning segments each. RNA blotting studies indicate that the beta-cell-type alpha 1 subunit is also expressed in brain as well as in the insulin-producing cell lines RINm5F and beta TC-3; however, it could not be detected by RNA blotting in a third cell line, HIT-T15. In situ hybridization studies revealed expression of beta-cell-type alpha 1 subunit mRNA in beta cells of rat pancreatic islets, implying that this protein may play a role in the regulation of insulin secretion.

Amino Acid Sequence↗
PubMed1992

Three-dimensional structure of the quinoprotein methylamine dehydrogenase from Paracoccus denitrificans determined by molecular replacement at 2.8 A resolution.

The three-dimensional structure of the quinoprotein methylamine dehydrogenase from Paracoccus dentrificans (PD-MADH) has been determined at 2.8 A resolution by the molecular replacement method combined with map averaging procedures, using data collected from an area detector. The structure of methylamine dehydrogenase from Thio-bacillus versutus, which contains an "X-ray" sequence, was used as the starting search model. MADH consists of 2 heavy (H) and 2 light (L) subunits related by a molecular 2-fold axis. The H subunit is folded into seven four-stranded beta segments, forming a disk-shaped structure, arranged with pseudo-7-fold symmetry. A 31-residue elongated tail exists at the N-terminus of the H subunit in MADH from T. versutus but is partially digested in this crystal form of MADH from P. denitrificans, leaving the H subunit about 18 residues shorter. Each L subunit contains 127 residues arranged into 10 beta-strands connected by turns. The active site of the enzyme is located in the L subunit and is accessible via a hydrophobic channel between the H and L subunits. The redox cofactor of MADH, tryptophan tryptophylquinone is highly unusual. It is formed from two covalently linked tryptophan side chains at positions 57 and 107 of the L subunit, one of which contains an orthoquinone.

Amino Acid Sequence↗
PubMed1992

Spinal epidural meningioma in a child.

A case of spinal epidural meningioma in a 14-year-old girl is presented. Myelographic and computed tomographic findings led to the preoperative diagnosis of a metastatic lesion. Histological examination revealed the tumor to be a meningioma. Total resection was accomplished and the patient made a very good neurological recovery. A review of the literature reveals that these tumors have rarely been reported, especially in childhood.

Adolescent↗
PubMed1992

Ovarian teratoma with gliomatosis peritonei.

Gliomatosis peritonei (GP) is a rare occurrence associated exclusively with ovarian teratoma (OT), in which numerous metastatic nodules composed mainly of mature glial tissue are studded on the peritoneum, omentum, and bowel wall. Two female patients (aged 5 years and 14 years) are reported. Various preoperative examinations confirmed a large abdominal teratoma with normal alpha-fetoprotein and beta-HCG. The OT was excised and partial omentectomy and incidental appendectomy were performed to remove as many metastatic nodules as possible. Pathological examinations including immunostains for glial fibrillary acidic protein showed predominantly mature glial tissue in the OT and in the metastatic nodules. An addition, chemotherapy was given to one of them, but both were well without recurrent diseases 17 months and 12 months postoperatively, respectively. The outcome of these two cases, in contrast to advanced malignancy in widespread intraperitoneal metastases of any other kind, supports the concept of benign nature of GP and a conservative surgical approach to this rare disorder.

Adolescent↗
PubMed1992

Quantitative immunoassay of total cellular GAP junction protein connexin32 during liver regeneration using antibodies specific to the COOH-terminus.

A radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA) were used to determine relative concentrations of liver connexin32 (CX32) in rats. The RIA and ELISA utilize synthetic peptides corresponding to regions of the carboxyl-terminus and antibodies raised in rabbits against these peptides. Assuming that affinities of antisera are similar for peptide and native CX32, total cellular CX32 was found to exceed the amount of gap junction protein at the cell surface calculated from morphometric analyses by 1.5-2.0 fold. This finding raises the possibility that some of the protein is present in cytoplasmic compartments or as occult precursors in the plasma membrane. Studies of CX32 content in regenerating rat liver support this conclusion and show a time course of loss and recovery of CX32 that agrees with those reported in studies using other techniques.

Animals↗
PubMed1992

Modification of the DiSC assay by the incorporation of monoclonal antibody staining.

The use of immunohistochemical staining with the DiSC assay is described. This modified staining procedure allows differentiation of viable human tumor cells from normal cells in biopsy preparations, facilitating the evaluation of slides from chemosensitivity assays. Samples from ALL and CLL patients were processed using both the DiSC and modified MoAb-DiSC procedure. The predictive results were compared and found to be identical. This procedure is advantageous in determining the chemosensitivity of tumor cells in a highly heterogeneous biopsy specimen.

Antibodies, Monoclonal↗
PubMed1992

Enhancement of interleukin 6 cytostatic effect on human breast carcinoma cells by soluble IL-6 receptor from urine and reversion by monoclonal antibody.

Interleukin 6 receptor soluble urinary protein (IL-6-R-SUP), a purified urinary protein binding IL-6 and identified as a truncated 50 kDa soluble form of the 80 kDa IL-6 cellular receptor, was tested for its biological activity. Addition of IL-6-R-SUP enhances the growth stimulation of mouse plasmacytoma T1165 by subliminal concentrations of human recombinant IL-6. Since this effect could be due to a lower affinity of human IL-6 for the mouse cell receptor, we tested the effect of IL-6-R-SUP on human cells. We show that the growth-inhibitory effect of IL-6 on breast carcinoma cells is enhanced by addition of IL-6-R-SUP to these human cells although they possess abundant IL-6 receptors. With IL-6-R-SUP, complete growth inhibition by IL-6 could be achieved and the cells became more sensitive to low levels of IL-6. These effects were prevented by a monoclonal antibody against IL-6-R-SUP which blocks IL-6 binding to cells. The naturally occurring IL-6-R-SUP may help to increase the growth-regulatory action of IL-6.

Animals↗
PubMed1992

Seventh cervical nerve root transfer from the contralateral healthy side for treatment of brachial plexus root avulsion.

Cervical root nerve transfer from the contralateral side has been used for the treatment of brachial plexus root avulsion in 49 patients. Resection of C7 root from the healthy side has produced no long-term symptoms or signs. Nine patients with ten recipient nerves have been followed up for more than two years and seven have obtained a functional recovery. This operation offers a new approach for the treatment of brachial plexus root avulsion.

Adolescent↗
PubMed1992

Neuropsychological impairment in anorexia nervosa: before and after refeeding.

Neuropsychological measures were administered to 18 patients with anorexia nervosa shortly after admission to hospital and again after substantial weight gain. These patients were compared with a group of 18 normal weight controls, also tested on two occasions, who were matched for age, sex, and estimated premorbid IQ. At low weight, impairment was evident on tests of attentional-perceptual-motor functions and on tests of visuospatial construction and problem-solving. Learning was less affected. Refeeding resulted in significant improvements in performance.

Adult↗
PubMed1992

Elevation of intracellular free calcium levels in sperm in response to long-term feeding of fungicides to mice.

To assess the impact of long-term feeding of fungicides on sperm quality, mice were fed a daily diet containing a mixture of maneb and zineb, at concentrations of 30, 300, and 3000 ppm, respectively. Employing epididymal sperm suspended in a medium permitting in vitro capacitation, the intracellular free Ca2+ concentration, [Ca2+]i, was determined with a fluorescent Ca2+ indicator, Fura-2. Regardless of the fungicide dosages applied, [Ca2+]i was about 50 percent higher in treated animals relative to a value of 123 nM [Ca2+]i in the control group. Fungicide-treated mice were mated to mature, non-treated females; as in the control, the litter sizes were the same. In conclusion, the observed elevation in [Ca2+]i seems to reflect cellular adaptation responses to toxic stress at moderate fungicide doses.

Animals↗
PubMed1992

The use of antisense oligonucleotides to establish autocrine angiotensin growth effects in human neuroblastoma and mesangial cells.

Local renin-angiotensin systems (RAS) exist in many cell types, and angiotensin II (AII) has growth regulatory effects in some tissues. We demonstrated the presence of angiotensinogen (ANG) mRNA in cultured human mesangial cells (MC) and SHSY-5Y human neuroblastoma cells using reverse transcription and the polymerase chain reaction (RT/PCR) followed by hybridization to a human ANG-specific oligonucleotide probe. We speculated, therefore, that AII might act in an autocrine or paracrine fashion to regulate the growth of mesangial cells and neuroblastoma cells. Sense and antisense oligonucleotides were next synthesized complementary to the ANG transcription start site. Antisense but not sense oligonucleotides decreased [3H]thymidine incorporation into DNA by both MC and neuroblastoma cells. Growth of antisense oligonucleotide-treated cells was restored to control levels by the addition of AII but not by the addition of basic fibroblast growth factor. Neither oligonucleotide affected [3H]thymidine incorporation in mouse L929 cells. These data indicate that locally produced AII can act in an autocrine or paracrine fashion to alter the growth of human mesangial and neuroblastoma cells. Therefore, they suggest a role for local RAS in the pathogenesis of growth abnormalities in the cardiovascular system as well as in some forms of malignancy.

Angiotensin II↗
PubMed1992

3-D structure of a mutant (Asp101-->Ser) of E.coli alkaline phosphatase with higher catalytic activity.

Mutagenesis of the absolutely conserved residue Asp101 of the non-specific monoesterase alkaline phosphatase (E.C. 3.1.3.1) from E. coli has produced an enzyme with increased kcat. The carboxyl group of the Asp101 residue has been proposed to be involved in the positioning of Arg166 and the formation of the helix that contains the active site Ser102. The crystal structure of the Asp101-->Ser mutant has been refined at 2.5 A to a final crystallographic R-factor of 0.173. The altered active site structure of the mutant is compared with that of the wild-type as well as with the structures of the mutant enzyme soaked in two known alkaline phosphatase inhibitors (inorganic phosphate and arsenate). The changes affect primarily the side chain of Arg166 which, by losing the hydrogen bond interaction with the carboxyl side chain of Asp101, becomes more flexible. This analysis, in conjunction with product inhibition studies of the mutant enzyme, suggests that at high pH (> 7) the enzyme achieves a quicker catalytic turnover by allowing a faster release of the product.

Alkaline Phosphatase↗
PubMed1992

Distribution of alcohol dehydrogenase and the low Km form of aldehyde dehydrogenase in isolated perivenous and periportal hepatocytes in rats.

UNLABELLED: Hepatic damage induced by chronic alcohol abuse starts in the perivenous (PV) zone of the hepatic lobule. To explain this vulnerability in the PV zone, periportal (PP) and PV hepatocytes were isolated by digitonin-collagenase perfusion and the distributions of class I alcohol dehydrogenase (ADH) and the low-Km mitochondrial aldehyde dehydrogenase (ALDH) were studied. ADH was measured by three approaches i.e., specific activity, immunoreactive enzyme content and ADH mRNA level. ALDH was determined by specific activity and immunoreactive enzyme content. When compared with PV hepatocytes, isolated PP cells exhibited higher lactate dehydrogenase (PP/PV = 1.3-1.5), higher alanine aminotransferase (PP/PV = 1.7-1.9), but lower glutamine synthase (PP/PV less than 0.01). By prelabeling the PP zone with acridine orange before digitonin-collagenase digestion, flow cytometry indicated that mainly the isolated PP hepatocytes exhibited fluorescence. ADH activities and ADH mRNA levels did not differ in PP and PV cells. With a polyclonal antibody directed specifically against class I ADH, ADH immunoreactive protein also did not differ in PP vs PV cells. By activity assay, the low Km ALDH activities were found to be lower in the PV hepatocytes (PP/PV = 1.3). This was confirmed by immunotransblot with anti-ALDH IgG (PP/PV = 1.6). IN CONCLUSION: the preferential damage of the PV zone produced by ethanol is not caused by differences of ADH distribution in liver but could be related partly to a decrease in the low-Km ALDH in the PV zone.

Alcohol Dehydrogenase↗
PubMed1992

Highly polymorphic XbaI RFLPs of the human 21-hydroxylase genes among Chinese.

A highly polymorphic XbaI restriction site flanking the human 21-hydroxylase genes (21-OHA and 21-OHB) was found with the probe pC21/3c, the cDNA of the 21-hydroxylase gene. From the results of RFLP analysis of 10 subjects with congenital adrenal hyperplasia (CAH) owing to 21-hydroxylase deficiency and their parents, at least four polymorphic fragments (30 kb, 27 kb, 25 kb, and 15 kb) resulting from cleavage at the polymorphic endonuclease sites outside the genes were found, and at least 10 different polymorphic patterns were observed among Chinese. These results indicate that these polymorphic loci are very informative for prenatal diagnosis of 21-hydroxylase deficiency.

Adrenal Hyperplasia, Congenital↗
PubMed1992

Coordinate regulation of amylin and insulin expression in response to hypoglycemia and fasting.

Amylin is a 37-amino acid peptide synthesized in the pancreatic beta-cell and cosecreted with insulin. In situ hybridization of nondiabetic rat pancreas shows that insulin and amylin RNA are both localized within the islet of Langerhans in a similar distribution. After 12 days of insulin-induced hypoglycemia (mean blood glucose 3.0 +/- 0.4 mM [54 +/- 8 mg/dl]), both insulin and amylin RNA fell greater than 95%. However, maintenance of euglycemia by simultaneous infusion of glucose with insulin did not suppress insulin or amylin RNA. Fasting suppressed amylin and insulin secretion from the isolated, perfused pancreas 70 and 58%, respectively, and with refeeding, secretion rates recovered to fed levels. Despite these changes in the rates of secretion, the relative ratio of amylin to insulin was not significantly different in fed, fasted, or refed rats. The molar ratio of insulin to amylin was estimated to be 100:2.3-2.6. Both insulin and amylin RNA was suppressed approximately 50% in response to fasting. Thus, although the absolute amounts of insulin and amylin change substantially under the conditions tested, the relative amounts of these peptides do not change.

Amyloid↗
PubMed1992

Influences of ginsenosides Rb1, Rb2, and Rb3 on electric and contractile activities of normal and damaged cultured myocardiocytes.

Free radical damage to the cultured myocardiocytes of Wistar rat was induced by adding xanthine 0.42 mmol.L-1 and xanthine oxidase 5.3 nmol.L-1 to the culture medium. 30 micrograms.ml-1 of Rb1, Rb2 or Rb3 extracted from the leaf and stem of Panax ginseng C A Meyer restored the action potentials (AP) of free radical damaged cells to normal, indicating their antioxidative action. On normal myocardial cells, Rb1, Rb2, Rb3 20 micrograms.ml-1 inhibited the AP and spontaneous contractility, (suggesting the Ca channel blockade action of panaxadiol saponins). The degrees of their inhibitory effects were found to be Rb1 > Rb2 > Rb3. Their effects against X-XO were basically the same.

Action Potentials↗