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Z Liu

Publications and source records attributed to Z Liu.

At least 703 records · Page 39Linked to original sources
PubMed1998

A model neuron with activity-dependent conductances regulated by multiple calcium sensors.

Membrane channels are subject to a wide variety of regulatory mechanisms that can be affected by activity. We present a model of a stomatogastric ganglion (STG) neuron in which several Ca2+-dependent pathways are used to regulate the maximal conductances of membrane currents in an activity-dependent manner. Unlike previous models of this type, the regulation and modification of maximal conductances by electrical activity is unconstrained. The model has seven voltage-dependent membrane currents and uses three Ca2+ sensors acting on different time scales. Starting from random initial conditions over a given range, the model sets the maximal conductances for its active membrane currents to values that produce a predefined target pattern of activity approximately 90% of the time. In these models, the same pattern of electrical activity can be produced by a range of maximal conductances, and this range is compared with voltage-clamp data from the lateral pyloric neuron of the STG. If the electrical activity of the model neuron is perturbed, the maximal conductances adjust to restore the original pattern of activity. When the perturbation is removed, the activity pattern is again restored after a transient adjustment period, but the conductances may not return to their initial values. The model suggests that neurons may regulate their conductances to maintain fixed patterns of electrical activity, rather than fixed maximal conductances, and that the regulation process requires feedback systems capable of reacting to changes of electrical activity on a number of different time scales.

Action Potentials↗
PubMed1998

Episodic ataxia type-1 mutations in the hKv1.1 cytoplasmic pore region alter the gating properties of the channel.

Episodic ataxia type-1 is a rare human neurological syndrome which occurs during childhood and persists through the whole life of affected patients. Several heterozygous point mutations have been found in the coding sequence of the voltage-gated potassium channel gene hKv1.1 of different affected families. V408A and E325D mutations are located in the cytoplasmic putative pore region of hKv1.1 channels and profoundly alter their gating properties. V408A channels showed increased kinetic rates of activation, deactivation and C-type inactivation. Expression of E325D channels in Xenopus oocytes led to an approximately 13-fold current amplitude reduction and to a 52.4 mV positive shift in the voltage dependence of activation. Moreover, the E325D mutation altered the kinetics of activation, deactivation, C-type inactivation and channel open probability. Heteromeric channels composed of two wild-type and two mutated subunits, linked as dimers, showed gating properties intermediate between channels formed from four normal or four mutated subunits. The results demonstrate that the highly conserved residues Val408 and Glu325 play a pivotal role in several gating processes of a human potassium channel, and suggest a pathogenetic mechanism by which the impairment of the delayed-rectifier function of affected neurons is related to the type and number of mutated subunits which make up the hKv1.1 channels.

Animals↗
PubMed1998

The nature of the minimal 'selenocysteine insertion sequence' (SECIS) in Escherichia coli.

The UGA codon, usually a stop codon, can also direct the incorporation into a protein of the modified amino acid selenocysteine. This UGA decoding process requires a cis -acting mRNA element called 'selenocysteine insertion sequence' (SECIS) that can form a stem-loop structure. In Escherichia coli the SECIS of the selenoprotein formate dehydrogenase (FdhH) mRNA has been previously described to consist of at least 40 nucleotides following the UGA codon. Here we determined the nature of the minimal SECIS required for the in vivo UGA-directed selenocysteine incorporation in E.coli . Our study is based on extensive mutational analysis of the fdhF SECIS DNA located in a lac' Z fusion. We found that the whole stem-loop RNA structure of the E.coli fdhF SECIS previously described is not required for the UGA-directed selenocysteine incorporation in vivo . Rather, only its upper stem-loop structure of 17 nucleotides is necessary on the condition that it is located in a proper distance (11 nucleotides) from the UGA codon. Based on these observations, we present a new model for the minimal E.coli SECIS.

Base Sequence↗
PubMed1998

[Cytochrome P450*2D6 gene polymorphism in Chinese population].

OBJECTIVE: To demonstrate the cytochrome P450*2D6(CYP*2D6) gene polymorphism distribution in Chinese. METHODS: The polymorphisms of CYP*2D6 gene in 100 Chinese people were studied with polymerase chain reaction and Xba I restriction fragment length polymorphic (RFLP) techniques. RESULTS: The frequencies of CYP*2D6 gene A, B, D and E mutations were 1%, 6.5%, 0.5% and 1%, respectively; the genotypes of 29kb/29kb,44kb/29kb and 44kb/44kb Xba I RFLP were 38%, 46% and 13%, respectively. It was found that 12% of B mutations were linked with even though A and B mutations were mainly associated with 29kb/29kb genotype. CONCLUSION: The frequencies of the four kinds of CYP*2D6 gene mutation in Chinese were lower than those of the European, but the frequency of Xba I 44kb allele was a little higher.

Adult↗
PubMed1998

Studies on the Synthesis of Elegan-Type Linear Diterpenes: The Efficient Total Syntheses of Eleganolone, Eleganolone Acetate, Elegandiol, Eleganonal, and Epoxyeleganolone

The first total syntheses of five elegan-type linear diterpenes-eleganolone (1), eleganolone acetate (2), elegandiol (3), eleganonal (4), and epoxyeleganolone (5)-were accomplished starting from (E,E)-farnesol (6) via four to six steps, successively, with high overall yield. The key step was the alkylation reaction of silyl cyanide with allylic iodide.

Journal Article↗
PubMed1998

A novel and practical route to A-ring enyne synthon for 1 alpha,25-dihydroxyvitamin D3 analogs: synthesis of A-ring diastereomers of 1 alpha,25-dihydroxyvitamin D2 and 3-methyl-1,25-dihydroxyvitamin D3.

A novel and practical route to the A-ring enyne synthon (2), which can be versatile for a variety of A-ring analogs of 1 alpha,25-dihydroxyvitamin D3 (1), was developed. This novel method led to an improved synthesis of the A-ring diastereomers of 1, the compounds 13-15, and synthesis of the new analogs, 2-methyl-1,25-dihydroxyvitamin D3 (4) with its all possible diastereomers. The biological evaluation of the 2-methyl analogs showed the alpha alpha beta-isomer to be more potent than 1.

Calcitriol↗
PubMed1998

Persistent allopeptide reactivity and epitope spreading in chronic rejection of organ allografts.

The role of the indirect allorecognition pathway in acute allograft rejection has been documented both in organ recipients and in experimental models. However, it is unknown whether self-restricted recognition of donor alloantigens also contributes to chronic allograft rejection. The aim of this study was to determine the relationship between allopeptide reactivity, epitope spreading, and chronic rejection. Using synthetic peptides corresponding to the hypervariable region of 32 HLA-DR alleles, we have followed the specificity of self-restricted T cell alloresponses to the donor in a population of 34 heart allograft recipients. T cells from sequential samples of blood collected from the patients up to 36 mo after transplantation were studied in limiting dilution analysis for allopeptide reactivity. The incidence of coronary artery vasculopathy (CAV) was significantly higher in patients who displayed persistent alloreactivity late after transplantation than in patients who showed no alloreactivity after the first 6 mo after transplantation. Both intra- and intermolecular spreading of epitopes was observed with an increased frequency in patients developing CAV in less than 2 yr, compared with patients without CAV; this suggests that diversification of the immune response against the graft contributes to chronic rejection. These data provide a strategy for identifying patients at risk of developing CAV and a rationale for therapeutic intervention aimed to prevent the progression of the rejection process.

Adult↗
PubMed1998

Rapid analysis of steroidal saponin mixture using electrospray ionization mass spectrometry combined with sequential tandem mass spectrometry.

Using electrospray ionization mass spectrometry (MS) combined with sequential tandem MS(ESI-MSn), two major steroidal saponins extracted from Tribulus terrestris were studied, and considerable useful structural information was obtained. The structure of the proposed known steroidal saponin was verified, and the structure of the unknown saponin was investigated using MSn experiments. Some special fragment ions were also observed, and the corresponding fragmentation mechanisms were investigated which are characteristic for steroidal saponins and can give some information on the linkage position of some sugar groups in saponins. This methodology has been established as a powerful tool for the rapid, comparative analysis of mixtures such as crude plant extracts.

Carbohydrate Sequence↗
PubMed1998

Electrophoretic affinity chromatography: method validation.

A new method for preparative-scale separation of biomolecules, electrophoretic affinity chromatography (EAC), is proposed in this paper. Separation by EAC is carried out in a long and ribbon-like multicompartment electrolyser separated by membranes, in which the two central compartments are used for packing the gel matrix and for sample loading respectively. Next to the central compartments are the elution compartments and electrode compartments. The electric field is applied perpendicular to the fluid flow in the compartments. Adsorption and desorption steps may both be carried out in the presence of an electric field, which transports the target components into the gel compartment for adsorption and the impurities into the elution compartments for washing. After the adsorption step an elution solution is introduced and the product is released from the gel matrix and washed out. Separation of human serum albumin (HSA) from human serum gives HSA product of high purity, as demonstrated by isoelectric focusing analysis. The characteristics of electrophoretic binding of HSA on Blue Sepharose Fast Flow are examined. The preliminary results show that this new method has advantages in terms of high rate of mass transfer and ease of scaling up, which are of particular interest when large-scale separation of biomolecules is considered.

Adsorption↗
PubMed1998

Interleukin-6, hepatocyte growth factor, and their receptors in biliary epithelial cells during a type I ductular reaction in mice: interactions between the periductal inflammatory and stromal cells and the biliary epithelium.

The interleukin-6 (IL-6)/gp-80 and hepatocyte growth factor (HGF)/met ligand/receptor systems have been shown to stimulate biliary epithelial cell (BEC) DNA synthesis in vitro. The mRNA and protein production of these two in vitro mitogens were mapped in vivo during the first week after bile duct ligation (BDL) when peak BEC DNA synthesis is seen. Changes around the biliary tree were compared with those seen in the peripheral liver using a combination of Northern blotting and a unique biliary tree isolation technique, in which the bile ducts and the surrounding portal stroma and inflammatory cells are separated from the hepatocytes by perfusion digestion. Further localization was performed with in situ hybridization and immunohistochemistry. In the normal liver, there is low-level expression of HGF mRNA by periportal stellate cells, and HGF protein localizes to these cells and to neutrophils; extracellular HGF protein is present in the bile. There is no detectable IL-6 mRNA by Northern analysis or IL-6 protein expression in the normal liver, but both met and IL-6 receptor (IL-6R) mRNA are detectable; met mRNA is expressed strongly in the biliary tree, and met protein is expressed weakly on hepatocytes and strongly on BEC. IL-6R mRNA is weakly expressed in the biliary tree, and IL-6R protein is detectable on hepatocytes, with a periportal-to-perivenular gradient, but not on BEC. During the first 3 days after BDL, HGF mRNA expression is increased in both the biliary tree and in the peripheral liver, and production is localized to stellate cells, periductal neutrophils, and stromal cells, which typically accompany the proliferating ductules. IL-6 mRNA and protein were detected only near the biliary tree after BDL, and not in the peripheral liver, and the production was localized to periductal hematolymphoid cells, which had the morphological appearance of macrophages and/or dendritic cells. There is also a distinct up-regulation of met and gp-80 mRNA and protein in the biliary tree, which is stronger than that seen in the peripheral liver. Met protein expression is increased, and IL-6R(gp-80) protein is induced on the proliferating BEC, consistent with the participation of both the HGF/met and IL-6/gp-80 systems in the early phases of type I ductular reactions. These observations show that periductal hematolymphoid and stromal cells are the source of BEC growth factors, and receptors for these factors are up-regulated on BEC during active ductular proliferation. Complex interactions between the inflammatory, stromal, and BEC results in a dysmorphogenic repair response that eventually leads to cirrhosis.

Animals↗
PubMed1998

Osmotic effects on volume and motility of bull sperm exposed to membrane permeable and nonpermeable agents.

Factorially arranged experiments were designed to study prefreeze packed cell volume (PCV) changes and associated percentages of motile and unstained bull sperm in simple macromolecule-free Tyrode's solution and egg yolk-Tris (EYT), varying in osmolarity, and with addition of rapidly permeating cryoprotectants, glycerol and 1,2-propanediol, and nonpermeating substances, sucrose and NaCl. The percentage of motile and unstained sperm was assessed after resuspending sperm in 300 mOsm/L Tyrode's solution. At 25 degreesC PCV increased in Tyrode's solution as osmolarity was decreased from 250 to 150 mOsm/L and decreased as Tyrode's solution was increased to 400 mosmol/L. The relationship of PCV to the reciprocal of the osmolarity was essentially linear over the range of 150 to 400 mOsm/L, but PCV did not decrease further in solutions ranging from 500 to 1000 mOsm/L. The percentage of motile sperm declined to zero in Tyrode's solution at 700 mOsm/L, but 40% of the sperm were still unstained in 1000 mOsm/L solutions. The addition of glycerol or 1,2-propanediol had little effect on PCV. With glycerol or 1,2-propanediol added to 308 mOsm/L Tyrode's solution to give a total of 1267 mOsm/L, there were 49 and 56% motile sperm, respectively, compared to 1% with NaCl added to give 787 mOsm/L. The PCV and percentage of motile sperm suspended in EYT responded to osmotic changes similar to those reported for Tyrode's solution at both 25 and 5 degreesC. Some sperm remained motile after initial exposure to 800 mOsm/L solutions. These findings may have application in improving bull sperm cryopreservation.

Animals↗
PubMed1998

Survival of bull sperm frozen at different rates in media varying in osmolarity.

The effects of freezing procedures, osmolarity, trehalose, and sucrose on survival of bull sperm in whole milk (WM) and egg yolk-Tris (EYT), semen extenders used worldwide, were studied. Sperm were added to extenders at 25 degreesC, cooled slowly to 5 degreesC, glycerolated, packaged in 0.5-ml straws, and frozen. Different freezing rates were accomplished in two steps. Straws were transferred from +5 degreesC to nitrogen vapor at temperatures ranging from -10 to -100 degreesC in the first step and to liquid nitrogen in the second step. Straws were thawed in water at 35 degreesC. A substantial decrease in sperm motility occurred between -10 and -20 degreesC, as abrupt nucleation occurred following supercooling to -13 degreesC. To study the interactions between osmolarity x cooling rate, WM and EYT extenders were prepared to yield media measuring 220 to 420 mOsm/L. The optimal first-step range of cooling in the two-step procedure was -30 to -70 degreesC, and the highest proportions of motile sperm after freezing and thawing were 61 to 62 in 260 to 300 mOsm/L WM and 63 to 64% in 300 to 340 mOsm/L EYT, equivalent to the results with the control procedure used commercially. As the cooling rate increased (first step to -100 degreesC) sperm motility was much higher in hypertonic than in hypotonic extenders (P < 0.05), indicating the importance of partial dehydration before rapid cooling. Replacing part of EYT and WM with equivalent solutions (same mOsm/L) of sucrose or trehalose had no appreciable effect. These results provide a basis for further investigating simple freezing systems that might be more effective in preserving bull sperm than those currently available.

Animals↗
PubMed1998

Infrared Laser Velocity Modulation Spectroscopy of SiCl+(X1Sigma+) up to v = 6.

Many fundamental and hot band absorption lines of 28Si35Cl+, 28Si37Cl+, 29Si35Cl+, and 30Si35Cl+ have been detectedbetween 630 and 700 cm-1 in a SiCl4/He discharge using diode laser velocity modulation spectroscopy. The datahave been fitted to give seven mass independent coefficients Ukl. The derived spectroscopic constants for 28Si35Cl+ include omegae = 678.24316(18) cm-1 and Be = 0.2870288(14) cm-1. The equilibrium internuclear distance is re =1.9439105(46) Å. The equilibrium dissociation energy calculated from Dunham's expanded Morse potential is De =49 431(57) cm-1. Copyright 1998 Academic Press.

Journal Article↗
PubMed1998

Infrared Diode Laser Spectroscopy of Fundamental and Hot Bands of BBr (X1Sigma+).

Infrared absorption spectra of the four common isotopic forms of the transient molecule BBr (11B79Br, 11B81Br, 10B79Br, and 10B81Br) have been observed in natural abundance. The spectra were detected in the region between 650 and 720 cm-1 using diode laser spectroscopy of a BBr3/He ac discharge. Over 150 lines consisting of both fundamental and hot bands up to v" = 5 have been fitted to Watson's isotopically invariant coefficients (Ukl). Spectroscopic parameters for each isotopomer could be derived from these coefficients; for 11B79Br, omegae = 685.1892(15) cm-1 and omegaexe = 3.73632(95) cm-1. The equilibrium dissociation energy obtained from Dunham's expanded Morse potential is 32 711(43) cm-1. Copyright 1998 Academic Press.

Journal Article↗
PubMed1998

Effect of procaine hydrochloride on cyanide intoxication and its effect on neuronal calcium in mice.

Cyanide intoxication in mice can be antagonized by the local anesthetic, procaine HCI, either alone or in combination with sodium nitrite and/or sodium thiosulfate. Antitoxic potency, derived from LD50 values, was compared in groups of mice pretreated with sodium nitrite (43.9 mg/kg i.p.), sodium thiosulfate (1 g/kg i.p.), and procaine HCI (37.0 mg/kg i.p.) either alone or in various combinations. The results of present study indicated that procaine HCI provides a significant protection against the lethal effects of potassium cyanide. Dose-response studies revealed procaine hydrochloride pretreated 3 min before KCN, at doses of 18.48-73.9 mg/kg, produced significant elevation of KCN LD50, moreover it has a good dose-effect relationship, but its antidotal effect was weaker than sodium nitrite or sodium thiosulfate when they were administered alone. The protective effect of sodium nitrite and sodium thiosulfate was enhanced with procaine HCI. When procaine was administered in combination both with sodium nitrite and sodium thiosulfate, its protective effects were further enhanced. Its antitoxic potency is 6.22. The effects of procaine on antagonizing the cyanide-induced whole-brain total calcium increase were also studied. KCN (7 mg/kg i.p.) significantly increased whole-brain total calcium level from 28.37 +/- 0.75 to 48.05 +/- 1.06 mg/g dry wt within 30 min, which can be prevented by procaine pretreated 15 min before KCN. One of the possible mechanism of procaine on antagonizing cyanide toxicity seems, at least, related to its effect on inhibiting the cyanide-induced neuronal calcium increase and maintaining the homeostasis of neuronal calcium.

Anesthetics, Local↗
PubMed1998

Human pregnancies after transfer of fresh (four- to eight-cell) versus frozen-thawed blastocysts resulting from intracytoplasmic sperm injection.

PURPOSE: The objective of this study was to obtain expanded blastocysts following intracytoplasmic sperm injection (ICSI) and Vero-cell co-culture, cryopreserve them at this stage, and transfer the frozen-thawed blastocysts to obtain pregnancies. METHODS: Twenty-two couples with severe male-factor infertility or failed fertilization in a previous in vitro fertilization cycle were included in this study. ICSI was performed for all of them, and sperm-injected oocytes were immediately subjected to Vero-cell co-culture for varying intervals. Then 14 couples were treated by embryo transfer at the four- to eight-cell stage (Group I), whereas 8 couples were treated by transfer of frozen-thawed blastocysts (Group II). RESULTS: Percentages of cleaved embryos and term survival rates were 57.1 and 73.3% for Group I and 50.0 and 37.5% for Group II, respectively. CONCLUSIONS: Blastocysts obtained after ICSI and Vero-cell co-culture can retain developmental competence after cryopreservation and thawing. Transfer of frozen-thawed blastocysts derived by these means holds promise for establishment of viable pregnancies.

Adult↗
PubMed1998

Rapid establishment of high-producing cell lines using dicistronic vectors with glutamine synthetase as the selection marker.

Recombinant proteins are useful tools in biological research, drug development, and drug screening. Specially designed expression vectors have been developed to introduce cDNA for recombinant protein expression in mammalian cells. We have combined a dicistronic mRNA design for expression of the recombinant protein, using glutamine synthetase (GS) for selection. A soluble form of human interleukin-4 receptor alpha chain was used as the model protein. The dicistronic vectors were compared to a standard expression vector in CHO-K1 cells in parallel experiments. Our data showed that a dicistronic vector containing an internal ribosome entry site (IRES) of the encephalomyocarditis virus (ECMV) was superior to a conventional expression vector in both levels of protein expression and amplification efficiency. The productivity of these clones was stable without selection pressure for an extended period of time. The GS selection system within a dicistronic vector design can achieve rapid and efficient gene amplification for protein production.

Alternative Splicing↗