Search PubMed⌕ Search

Biomedical subjects

N Liu

Publications and source records attributed to N Liu.

At least 235 records · Page 13Linked to original sources
PubMed1994

Enhanced chromosomal response of ataxia-telangiectasia cells to specific types of DNA double-strand breaks.

The chromosomal response of two ataxia-telangiectasia (A-T) lymphoblastoid cell lines (A-T-PA and A-T-KM) to restriction endonucleases (RE) is compared with that of a normal (N-SW) lymphoblastoid cell line. The RE used were PvuII (generating DNA double-strand breaks with blunt termini), BamHI (cohesive termini with 4 base, 5' overhangs) and PstI (cohesive termini with 4 base 3' overhangs). Chromatid aberrations were analysed in cells 5 h after treatment. Cells were porated using streptolysin O to allow entry of RE. Both A-T lines showed an enhanced frequency of chromatid breaks in G2 phase compared with normal cells in response to RE. The enhanced response of A-T cells was most marked in the case of PvuII treatment when the enhancement ratios were 2.5 and 4.2 for A-T-PA and A-T-KM respectively. However, the frequency of DNA double-strand breaks (dsb), measured by neutral filter elution, were considerably lower in A-T-PA cells than N-SW, due to a lower efficiency of poration. When A-T-PA cells were treated with streptolysin O at a higher concentration (0.3 Units/ml), a condition that apparently led to a similar level of poration in A-T-PA as in N-SW cells treated with 0.06 Units/ml as judged by the similar number of dsb induced in the two lines for a given PvuII concentration, the enhancement ratio for A-T-PA cells treated with PvuII increased from 2.5 to 5.8. BamHI and PstI were found to be less clastogenic in all three cell lines as found previously for Chinese hamster cells, although part of this effect may be due to a lower activity, particularly in the case of PstI. However, even at a 4-6-fold higher concentration, BamHI was still less clastogenic than PvuII. It is concluded that dsb with blunt termini are more clastogenic than those with cohesive termini. The results suggest that the chromosomal sensitivity of A-T cells may result from a defect causing a higher rate of conversion of dsb into chromatid aberrations.

Ataxia Telangiectasia↗
PubMed1994

[A study of computed tomography of elderly temporomandibular joint disorders syndrome (TMJDS) patients treated with and without splint in three dimensions].

The computed tomography of elderly TMJDS patients treated with and without splint were studied in three dimensions. The results showed that the condyle was in a retruded position in the glenoid fossa in sagittal dimension and the horizontal condylar angle appeared asymmetry in axial dimension. Under the splint treatment, the retruded condyle can be adjusted to the center of the glenoid fossa and the horizontal condylar angle can be balanced, since the splint may correct the vertical dimension and eliminate the occlusal interferences. This study indicates that the horizontal condylar angle can be considered as a significant factor in diagnosis of TMJDS and evaluation of the outcome of treatment.

Aged↗
PubMed1993

Comparison of cDNAs from bovine brain coding for two isoforms of calreticulin.

Calreticulin is a major calcium-binding protein of the endoplasmic reticulum of non-muscle cells. In addition to a 1.9-kb calreticulin mRNA, some evidence has suggested the existence of another transcript of 3.75 kb, which is very similar to calreticulin. We report here the isolation and sequencing of cDNA clones from a bovine brain lambda gt11 cDNA library, two of which appear to code for calreticulin and a third for a novel isoform of calreticulin. The deduced amino-acid sequence of the novel clone shares high similarity with mouse calreticulin in the C-terminal 318 amino acids. However, its N-terminal sequence is completely divergent. Northern blot analysis of bovine cerebral cortex RNA indicates that the conserved region of the clone hybridizes to two messages of 1.9 kb and 3.75 kb. The divergent region of this clone hybridizes to the 3.75-kb message, but not to the 1.9-kb message. We believe that this novel clone corresponds to an alternate form of calreticulin which is identical to calreticulin toward the C-terminus, but completely different at the N-terminal region, and that this isoform is encoded by a much larger message.

Amino Acid Sequence↗
PubMed1993

Cell-type specific interaction of Neu differentiation factor (NDF/heregulin) with Neu/HER-2 suggests complex ligand-receptor relationships.

The Neu/HER-2 receptor tyrosine kinase is overexpressed in some types of human adenocarcinomas, including tumors of the breast and the ovary. A 44 kDa glycoprotein that elevates tyrosine phosphorylation of Neu has been isolated and named Neu differentiation factor (NDF), or heregulin. Here we show that NDF affects tyrosine phosphorylation of Neu in human tumor cells of breast, colon and neuronal origin, but not in ovarian cells that overexpress the receptor. By using monoclonal antibodies (mAbs) to Neu, we found that the ovarian receptor is immunologically and biochemically similar to the mammary p185neu. Nevertheless, unlike breast-derived Neu, the ovarian protein did not display covalent cross-linking to radiolabeled NDF, and was devoid of ligand-induced association with phosphatidylinositol 3'-kinase. Direct binding analysis showed that NDF binds with high affinity (Kd approximately 10(-9) M) to mammary cells, but its weak association with ovarian cells is probably mediated by heparin-like molecules. Similar to the endogenous receptor, the ectopically overexpressed Neu of mammary cells, but not of ovarian and fibroblastic cells, exhibited elevated levels of NDF-induced phosphorylation and covalent cross-linking of the radiolabeled factor. Taken together, our results imply that NDF binding to cells requires both Neu and an additional cellular component, whose identity is still unknown, but its tissue distribution is more restricted than the expression of the neu gene.

Animals↗
PubMed1993

Phosphorylation and dephosphorylation events play critical roles in Sindbis virus maturation.

We have examined the effects of various inhibitors of protein kinases and phosphatases on Sindbis virus maturation in BHK cells. 2-aminopurine, a nonspecific protein kinase inhibitor, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7), a specific inhibitor of calmodulin/Ca(2+)-dependent protein kinase, and okadaic acid (OKA), a protein phosphatase inhibitor, dose-dependently inhibited Sindbis virus maturation. Although virus production was inhibited, the membrane glycoprotein precursors PE2/E1 were exported from the endoplasmic reticulum and PE2 was converted to E2 at normal kinetic rates. The glycoproteins were delivered to the plasma membrane in conformations which rendered them competent for low pH-mediated cell-cell fusion from within. Electron microscopy showed that in the presence of W-7, virus nucleocapsids were free in the cell cytoplasm, while in the presence of OKA, the nucleocapsids were associated with cell membranes. Metabolic labeling of Sindbis virus-infected cells with [32P]orthophosphate in the presence of OKA resulted in the specific labeling of the PE2/E2 glycoprotein. We have previously shown that the carboxyl terminus of the PE2 glycoprotein is initially buried in cell membranes and is then exposed to the cytoplasm at some later stage in virus maturation. The data shown are consistent with the hypothesis that phosphorylation and dephosphorylation play a critical role in a late stage in Sindbis virus maturation, possibly in releasing of the E2 tail from cell membranes.

2-Aminopurine↗
PubMed1993

Immunohistochemical evidence for different pathways immunoreactive to substance P and calcitonin gene-related peptide (CGRP) in the guinea-pig stellate ganglion.

The colocalization of immunoreactivities to substance P and calcitonin gene-related peptide (CGRP) in nervous structures and their correlation with other peptidergic structures were studied in the stellate ganglion of the guinea pig by the application of double-labelling immunofluorescence. Three types of fibre were distinguished. (1) Substance P+/CGRP+ fibres, which sometimes displayed additional immunoreactivity for enkephalin, constituted a small fibre population of sensory origin, as deduced from retrograde labelling of substance P+/CGRP+ dorsal root ganglion cells. (2) Substance P+/CGRP- fibres were more frequent; some formed baskets around non-catecholaminergic perikarya that were immunoreactive to vasoactive intestinal polypeptide (VIP). (3) CGRP+/substance P- fibres were most frequent and were mainly distributed among tyrosine hydroxylase (TH)-immunoreactive cell bodies. The peptide content of fibre populations (2) and (3) did not correspond to that of sensory ganglion cells retrogradely labelled by tracer injection into the stellate ganglion. Therefore, these fibres are thought to arise from retrogradely labelled preganglionic sympathetic neurons of the spinal cord, in which transmitter levels may have been too low for immunohistochemical detection of substance P or CGRP. CGRP-immunoreactivity but no substance P-immunolabelling was observed in VIP-immunoreactive postganglionic neurons. Such cell bodies were TH-negative and were spared by substance P-immunolabelled fibre baskets. Retrograde tracing with Fast Blue indicated that the sweat glands in the glabrous skin of the forepaw were the targets of these neurons. The streptavidin-biotin-peroxidase method at the electron-microscope level demonstrated that immunoreactivity to substance P and CGRP was present in dense-cored vesicles of 50-130 nm diameter in varicosities of non-myelinated nerve fibres in the stellate ganglion. No statistically significant difference in size was observed between vesicles immunolabelled for substance P and CGRP. Immunoreactive varicosities formed axodendritic and axosomatic synaptic contacts, and unspecialized appositions to non-reactive neuronal dendrites, somata, and axon terminals. Many varicosities were partly exposed to the interstitial space. The findings provide evidence for different pathways utilizing substance P and/or CGRP in the guinea-pig stellate ganglion.

Animals↗
PubMed1993

Transient translocation of the cytoplasmic (endo) domain of a type I membrane glycoprotein into cellular membranes.

The E2 glycoprotein of the alphavirus Sindbis is a typical type I membrane protein with a single membrane spanning domain and a cytoplasmic tail (endo domain) containing 33 amino acids. The carboxyl terminal domain of the tail has been implicated as (a) attachment site for nucleocapsid protein, and (b) signal sequence for integration of the other alpha-virus membrane proteins 6K and E1. These two functions require that the carboxyl terminus be exposed in the cell cytoplasm (a) and exposed in the lumen of the endoplasmic reticulum (b). We have investigated the orientation of this glycoprotein domain with respect to cell membranes by substituting a tyrosine for the normally occurring serine, four amino acids upstream of the carboxyl terminus. Using radioiodination of this tyrosine as an indication of the exposure of the glycoprotein tail, we have provided evidence that this domain is initially translocated into a membrane and is returned to the cytoplasm after export from the ER. This is the first demonstration of such a transient translocation of a single domain of an integral membrane protein and this rearrangement explains some important aspects of alphavirus assembly.

Amino Acid Sequence↗
PubMed1993

Partial reversal of the effects of extradural clonidine by oral yohimbine in postoperative patients.

Extradural clonidine produces analgesia, with sedation, hypotension and bradycardia, in postoperative patients. This study assessed if oral yohimbine would reverse these side effects. We studied 30 ASA I-II patients undergoing orthopaedic surgery. After operation they were allocated randomly to three groups to receive placebo, extradural clonidine 450 micrograms or extradural clonidine 450 micrograms plus oral yohimbine 16 mg. Pain score was measured on a visual analogue scale (VAS); sedation was assessed on a simple scale graded from 0 (awake and alert) to 3 (deeply sedated, awakening after tactile stimulations) and heart rate and arterial pressure were monitored for 5 h. Yohimbine reversed the sedation induced by extradural clonidine, but also shortened the duration of analgesia (31 (SD 15) min, 186 (72) min and 126 (52) min in the placebo, extradural clonidine and extradural clonidine+yohimbine groups, respectively) (P < 0.05), and did not reduce the hypotension and bradycardia related to clonidine administration. These results suggest that alpha 2 adrenoceptors are mediators of the sedation induced by clonidine and that the haemodynamic effects are not related to stimulation of supraspinal alpha 2 receptors.

Administration, Oral↗
PubMed1993

Radiosensitive Chinese hamster irs2 cells show enhanced chromosomal sensitivity to ionizing radiation and restriction endonuclease induced blunt-ended double-strand breaks.

The Chinese hamster irs2 cell line shows cellular hypersensitivity to ionizing radiation although the induction and repair of double-strand breaks (dsb) in bulk DNA is normal. Here we report that irs2 shows chromosomal hypersensitivity to ionizing radiation and the restriction endonuclease PvuII. The ratio of induced chromosomal aberrations in irs2 versus V79 was similar to that for survival (factor of between 2 and 4). PvuII was administered during cell poration with the bacterial toxin streptolysin O. We also report that when streptolysin O porated irs2 and V79 cells were treated with PvuII, and dsb assayed by neutral filter elution, equivalent numbers of dsb were induced in the two lines as a function of time following treatment. Our data show that irs2 has a DNA damage processing defect that leads to enhanced conversion of blunt-ended dsb into visible chromosomal damage.

Animals↗
PubMed1993

Response of ataxia telangiectasia cells to restriction endonuclease induced DNA double-strand breaks: I. Cytogenetic characterization.

Ataxia telangiectasia (AT) and normal human lymphoblastoid cell lines have been treated with either X-rays or the restriction endonucleases PvuII and BamHI using streptolysin-O poration, and the frequencies of micronuclei or chromosomal aberrations measured. We report that AT cells (AT-PA) are hypersensitive to the restriction endonucleases PvuII and BamHI, inducing DNA double-strand breaks (dsb) with either blunt or cohesive termini, respectively. Our data indicates that AT-PA cells have a dsb processing defect that leads to a higher rate of conversion of dsb into chromosomal aberrations than in normal cells. AT-PA cells showed up to a 5-fold enhanced sensitivity to PvuII over the normal (N-SW) line, a result of an increase in frequencies of chromatid aberrations. Chromosome-type aberrations appeared not to be increased in AT-PA cells over those induced in the normal N-SW line. Particularly striking was the appearance in AT-PA of high frequencies of chromatid aberrations at the 24 h sampling time. BamHI also caused enhanced aberration frequencies in AT-PA cells although the cohesive-ended dsb caused by BamHI still appeared to be less effective in causing chromosomal aberrations than the blunt-ended dsb caused by PvuII in both AT-PA and N-SW, as we have previously reported for Chinese hamster cells. The enhanced effectiveness of cohesive-ended dsb in AT-PA cells over normal cells may be a result of altered processing of dsb by AT-PA cells or may be caused by conversion of some cohesive-ended dsb into blunt-ended dsb by exonuclease digestion before ligation can take place.

Ataxia Telangiectasia↗
PubMed1993

Clonidine comparably decreases the thermoregulatory thresholds for vasoconstriction and shivering in humans.

BACKGROUND: Clonidine stops postoperative shivering, but its underlying mechanism of action is unknown. Clonidine may impair central control of thermoregulation or act on peripheral receptors. Accordingly, the authors tested the hypothesis that clonidine reduces both the vasoconstriction and shivering thresholds, a pattern consistent with central thermoregulatory impairment. METHODS: Seven healthy volunteers participated in the study. Thermoregulatory vasoconstriction was evaluated using forearm minus fingertip, skin-temperature gradients; values exceeding 4 degrees C were considered to be significant vasoconstriction. Systemic oxygen consumption (VO2) was measured with a canopy system. In addition, shivering was qualitatively evaluated using a simple scale, graduated from 0 (no shivering) to 2 (intense shivering). The tympanic membrane temperatures triggering significant vasoconstriction and grade 1 shivering were considered to be the thresholds for the two thermoregulatory responses. Measurements were performed after a 10-min steady state period and during cooling by central venous infusion of Ringer's lactate solution at 4 degrees C. Each subject was evaluated at two sessions, separated by at least 48 h. They were randomly and blindly assigned to received either an intravenous bolus of 75 micrograms clonidine or a placebo before cooling. When the shivering score equaled 2, 75 micrograms clonidine was injected intravenously, and repeated if necessary, to completely stop shivering.

Adult↗
PubMed1993

Improved quantitative Apt test for detecting fetal hemoglobin in bloody stools of newborns.

We devised an improved spectrophotometric method, based on the differential susceptibility of various hemoglobins to alkaline denaturation, to measure the percentage of fetal hemoglobin (HbF) in bloody meconium so as to determine the source of the blood. The oxyhemoglobin of a sample was spectrophotometrically scanned from 450 to 650 nm before and after the addition of sodium hydroxide. With Allen baseline correction, the ratio of absorbance at 576 nm was linearly proportional to the percentage of HbF in the specimen as described by the equation: ratio = 0.01 (%HbF) + 0.0045 (r = 0.9971, Sy/x = 0.047). Preliminary studies on samples containing 10% or 80% HbF revealed that the method was fairly precise. The accuracy of this test was verified by comparing the results (y) with those obtained by radial immunodiffusion (x): y = 0.997x + 2.93 (r = 0.91). This preliminary study demonstrates that the modified test is simple, fast, and free from bilirubin interference. It should be useful for the diagnosis of gastrointestinal bleeding of the newborn on a stat basis.

Color↗
PubMed1993

[Is there an advantage to using opioid combinations by the peridural route?].

Epidural opioids provide a potent analgesia not devoided of side effects. In addition, epidural administration of lipid soluble opioids has no clear advantage over the IV route. Combination of epidural opioids with other analgesics may strengthen analgesia and may decrease the incidence of side effects because of a reduction in the amount of opioid administered. Improvement in analgesia quality is documented when local anaesthetics are associated to opioids. Low concentrations of local anaesthetics may potentiate the effect of opioids on ions membrane channels at the level of the dorsal horn of the spinal cord. Alpha adrenergic agonists provide an alternative to local anaesthetics, allowing to improve pain control achieved with opioids. Epinephrine decreases plasma absorption of opioids and is especially useful to prolong the effect of short acting lipid soluble opioids. Alpha adrenergic agonists atc on alpha-2-adrenergic receptors of the spinal cord dorsal horn to depress pain nociceptive transmission. This effect potentiates the one of opioids at this level. Clonidine, which is a selective alpha-2-adrenergic agonist has been demonstrated to improve and to prolong analgesia produced by opioids in postoperative patients. Clonidine administration induces side effects, like sedation, bradycardia and hypotension, but allows to highly reduce the opioid dose. None of the combined techniques of analgesia implies that monitoring of the side effects of opioids has to be reduced.

Adrenergic alpha-Agonists↗
PubMed1992

Functional implication of disulfide bond, Cys250 -Cys283, in bovine chymosin.

The reduction, carboxymethylation and mercuration of disulfide bond, Cys250-Cys283, located on the surface of bovine chymosin molecule resulted in the loss of about 25% of enzyme activity, suggesting that Cys250-Cys283 is not intimately involved in catalytic mechanism. Cys250 and Cys283 were substituted with Asp. and Ser. by site- directed mutagenesis of the structural gene coding for bovine prochymosin B. All three mutants (C250D/C283S, C250D, C283S) failed to be activated to chymosin in acid, indicating that Cys250-Cys283 might have some contribution to the correct refolding of the unfolded prochymosin.

Animals↗