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M D Wang

Publications and source records attributed to M D Wang.

At least 37 records · Page 2Linked to original sources
PubMed1997

Pregnenolone sulphate and pregnenolone do not interact with 5 beta-pregnanolone- and hexobarbitone-induced anaesthesia in the rat.

We have studied the interaction of pregnenolone sulphate and pregnenolone with 5 beta-pregnanolone- and hexobarbitone-induced anaesthesia in male rats using an EEG threshold method. Burst suppression of the EEG of 1 s or more ("silent second" (SS)), was used as a criterion of deep anaesthesia. The effects of the steroid solvents albumin and beta-cyclodextrin were assessed by dose-response curves. Despite a significant increase in hexobarbitone threshold dose in relation to increased doses of albumin, there was no correlation between albumin dose and hexobarbitone concentrations in serum, fat and brain tissues. There was no significant difference in threshold concentrations of hexobarbitone between controls given albumin and those pretreated with pregnenolone. In subsequent experiments, 20% beta-cyclodextrin was used as steroid solvent and its volume was maintained at less than 3.0 ml kg-1 during pretreatment. Neither pregnenolone sulphate nor pregnenolone significantly altered the potency of 5 beta-pregnanolone for induction of anaesthesia. Furthermore, there was no interaction of pregnenolone sulphate and pregnenolone on induction of anaesthesia when hexobarbitone was used for anaesthesia.

Albumins↗
PubMed1995

Transcription against an applied force.

The force produced by a single molecule of Escherichia coli RNA polymerase during transcription was measured optically. Polymerase immobilized on a surface was used to transcribe a DNA template attached to a polystyrene bead 0.5 micrometer in diameter. The bead position was measured by interferometry while a force opposing translocation of the polymerase along the DNA was applied with an optical trap. At saturating nucleoside triphosphate concentrations, polymerase molecules stalled reversibly at a mean applied force estimated to be 14 piconewtons. This force is substantially larger than those measured for the cytoskeletal motors kinesin and myosin and exceeds mechanical loads that are estimated to oppose transcriptional elongation in vivo. The data are consistent with efficient conversion of the free energy liberated by RNA synthesis into mechanical work.

Biophysical Phenomena↗
PubMed1995

Potency of lipid and protein formulation of 5 alpha-pregnanolone at induction of anaesthesia and the corresponding regional brain distribution.

We have studied the anaesthetic potencies of 5 alpha-pregnanolone albumin solution (PAS) and 5 alpha-pregnanolone Intralipid emulsion (PLE) at equivalent concentrations in male rats using an EEG threshold method. The criterion of anaesthesia was burst suppression of the EEG of 1 s or more (the "silent second" (SS)) as a sign of deep anaesthesia. The potency of the two formulations was assessed by comparing the threshold doses of 5 alpha-pregnanolone at three dose rates (1.0, 2.0 and 3.0 mg kg-1 min-1). We found that SS was initiated in all rats after infusions of PAS, while no SS could be induced in rats after infusion of PLE at a larger dose. A higher concentration of 5 alpha-pregnanolone was found in all brain and peripheral tissues of PAS-treated rats than in those treated with PLE. In rats with PAS-induced anaesthesia (3.0 mg kg-1 min-1), the highest concentrations were detected in striatum (mean 19.40 (SD 1.21) ng mg-1). Although there was a small insignificant reduction in threshold doses with dose rates at 2.0-3.0 mg kg-1 min-1, the tissue concentrations in striatum, frontal cortex and occipital cortex were found to be significantly increased. We conclude that PAS was more potent than PLE in inducing anaesthesia. Brain distribution of 5 alpha-pregnanolone varied regionally in a manner similar to the variation in GABAA receptor sensitivity to this neuroactive steroid.

Albumins↗
PubMed1995

Team development and memory training in traumatic brain injury rehabilitation: two birds with one stone.

The need for developing team cooperation procedures when treating patients with traumatic brain injury (TBI) is stated. One approach in promoting team cooperation is to combine team development with a specific training programme. A memory training programme used in a subacute TBI rehabilitation unit is described. A combination of a team development procedure and memory training programme was performed in the unit. A questionnaire to assess team members' attitudes to team cooperation was administered before and after team development, and memory training procedures were implemented. The post-training questionnaire administration indicated a more positive perception among team members of how the team functioned. The efficacy of memory training showed variable results. The programme described may illustrate the advantages of combining a specific treatment programme with efforts to promote team development.

Adult↗
PubMed1995

[Inhibition of sodium artesunate on rat erythrocyte membrane Na(+)-K(+)-exchanging ATPase in vitro].

AIM: To study the effects of sodium artesunate (SA) on Na(+)-K(+)-exchanging ATPase activity of rat erythrocyte membrane in vitro. METHODS: SA of different concentrations (0, 0.5, 1, 5 and 10 mumol . L-1) were added respectively in the reaction system. The Na(+)-K(+)-exchanging ATPase activity was calculated by measuring the amount of inorganic phosphate released in the reaction system. RESULTS: Along with the increase of SA concentration (0, 0.5, 1, 5 and 10 mumol . L-1), the Na(+)-K(+) -exchanging ATPase activity decreased, the inhibitory rates were 15%, 29%, 46%, and 75%, respectively. Increasing the concentration of substrate ATP to 125, 250, 375 and 500 mumol . L-1 and determining the kinetics of enzyme. Making the Eadie-Hofstee kinetic curve by linear-regression analysis. The result revealed that the inhibitory effect of SA on the enzyme was competitive. CONCLUSION: SA affected the ion transfer of host erythrocyte membrane and membrane function.

Animals↗
PubMed1994

Time-lapse total internal reflection fluorescence video of acetylcholine receptor cluster formation on myotubes.

To study when and where acetylcholine receptor (AChR) clusters appear on developing rat myotubes in primary culture, we have made time-lapse movies of total internal reflection fluorescence (TIRF) overlaid with schlieren transmitted light images. The receptors, including the ones newly incorporated into the membrane, were labeled with rhodamine alpha-bungarotoxin (R-BT) continuously present in the medium. Since TIRF illuminates only cell-substrate contact regions where almost all of the AChR clusters are located, background fluorescence from fluorophores either in the bulk solution or inside the cells can be suppressed. Also, because TIRF minimizes the exposure of the cell interior to light, the healthy survival of the culture during imaging procedures is much enhanced relative to standard epi- (or trans-) illumination. During the experiment, cells were kept alive on the microscope stage at 37 degrees C in an atmosphere of 10% CO2. Two digital images were recorded by a CCD camera every 20 min: the schlieren image of the cells and the TIRF image of the clusters. After background subtraction, the cluster image was displayed in pseudocolors, overlaid onto the cell images, and recorded as 3 frames on a videotape. The final movies are thus able to summarize a week-long experiment in less than a minute. These movies and images show that clusters form often shortly after the myoblast fusion but sometimes much later, and the formation takes place very rapidly (a few hours). The clusters have an average lifetime of around a day, much shorter than the lifetime of a typical myotube. The brightest and largest clusters tend to be the longest-lived. The cluster formation seems to be associated with the contacts of myotubes at the glass substrate, but not with cell-cell contacts or myoblast fusion into myotubes. New AChR continuously appear in preexisting clusters: after photobleaching, the fluorescence of some clusters recovers within an hour.

Animals↗
PubMed1994

Reduction-of-dimensionality kinetics at reaction-limited cell surface receptors.

It has been suggested for several years that reactions between ligands and cell surface receptors can be speeded up by nonspecific adsorption of the ligand to the cell surface followed by two-dimensional surface diffusion to the receptor, a mechanism referred to as "reduction-of-dimensionality" (RD) rate enhancement. Most of the theoretical treatments of this and related problems have assumed that the receptor is an irreversibly absorbing perfect sink. Such receptors induce a depletion zone of ligand probability density around themselves. The reaction rate in this case (called "diffusion-limited") is limited only by the time required for ligands to diffuse through this depletion zone. In some cases, however, the receptor may be far from "perfect" such that a collision with a ligand only rarely leads to binding. Receptors then do not create significant local depletion zones of ligand probability density, and the reaction rate becomes strongly affected by the (small) probability of reaction success per diffusive encounter (the "reaction-limited" case). This article presents a simple theory of RD rate enhancement for reaction-limited receptors that are either reversible or irreversible binders. In contrast to the diffusion-limited theories, the reaction-limited theory presented here: (a) differs quantitatively from diffusion-limited models; (b) is simple and algebraic in closed form; (c) exhibits significant rate enhancement in some realistic cases; (d) depends strongly on the actual Brownian rather than pure diffusive nature of the ligand's motion; (e) depends (for irreversibly binding receptors only) on the kinetic rates (not just equilibria) of reversible adsorption to nontarget regions, in contrast to some previous approximate theories of reduction of dimensionality; and (f) is applicable to actual ligand/receptor systems with binding success probabilities at the opposite extreme from the perfect sink/diffusion-limited models.

Adsorption↗
PubMed1990

Elimination of z-ejection in Fourier transform ion cyclotron resonance mass spectrometry by radio frequency electric field shimming.

In Fourier transform ion cyclotron resonance (FT/ICR) mass spectrometry, coherent ion cyclotron orbital motion is produced by resonant radio frequency (rf) electric field excitation. However, because the excitation electrodes are of finite dimensions, the desired transverse (to the applied magnetic field) rf electric field is accompanied by an rf electric field component along the z- (magnetic field) direction, resulting in mass-dependent z-ejection and mass-dependent FT/ICR mass spectral peak relative magnitudes. Addition of several "guard wires" of voltage-divided rf amplitude allows the rf electric field to be "shimmed" to near-perfect uniformity. In this paper (see also the accompanying paper by Russell et al.), we introduce two types of rf-shimmed ion traps. In the first type, guard wires are placed only in front of the trapping electrodes. In the second type, guard wire rings are placed inside the detector and trapping electrodes. For either arrangement, simion simulations were used to adjust the rf voltages applied (by use of voltage dividers) to the guard wires or rings so as to produce an optimally uniform rf field within the trap. The virtual elimination of z-excitation is confirmed by plots of magnitude-mode relative peak height vs ICR orbital radius. Because the guard wires (or rings) tend to shield the ions from the trapping electrode potential, the shift in ICR frequency with trapping voltage is also reduced, but not as well as by a screened trap.(ABSTRACT TRUNCATED AT 250 WORDS)

Fourier Analysis↗
PubMed1990

[Effects of sodium artesunate on electrical properties and Na+,K(+)-ATPase activities of mouse small intestine].

Sodium artesunate (SA), a synthetic derivative of artemisinin first isolated in China, is a water soluble antimalaria used clinically in China. The jejunum of mouse was mounted in Ussing chambers and bathed in NaCl Ringer. There was a potential difference (PD) across the intestinal wall with the serosa being positive. Addition of SA to the mucosal side of the D-glucose (5.5 mmol/L) NaCl Ringer bathing solution, caused a significant decrease in both PD and short circuit current (I(sc)). However, SA had little effect when added to the glucose free Ringer bathing solution. SA 0.1-1.0 mmol/L caused a decrease in Na+,K(+)-ATPase activities in vitro. The results suggest that the inhibitory effect on the electrical properties of mouse jejunum is associated with the inhibition of Na+,K(+)-ATPase activities.

Animals↗
PubMed1988

Acquisition of new metabolic capabilities: multicopy suppression by cloned transaminase genes in Escherichia coli K-12.

The four general transaminases of Escherichia coli K-12 have overlapping, but discrete, substrate specificities and participate in the final step in the synthesis of at least seven different amino acids. Through the use of strains that have mutations in one or more transaminase genes and carry a different wild-type (wt) gene on a multicopy plasmid, it was possible to detect instances in which an amplified wt gene suppressed nonallelic mutations. In these cases, overproduction of the enzyme permitted a broader range of substrates to be used at physiologically significant levels, either because a low catalytic efficiency (in the case analyzed here) or a low affinity of the enzyme towards the substrate prevented its effective utilization under normal conditions. Consequently, by compensating for a low catalytic reaction rate, enzyme overproduction circumvents the original lesion and restores biosynthetic activity to the mutant strain. The suppression of a mutation in one gene by amplified copies of a different wt gene is termed 'multicopy suppression'. This phenomenon is useful for detecting poorly expressed genes, for detecting duplicate genes, for identifying secondary functions of the products of known genes, and for elucidating the metabolic role of the product of the suppressed gene.

Cloning, Molecular↗
PubMed1988

Rapid identification of bacterial genes that are lethal when cloned on multicopy plasmids.

A procedure to identify genes that are lethal when cloned on multicopy plasmids was developed. It depends on the ability of mini-Mu plasmid elements to be used for both in vivo cloning and generalized transduction of enterobacterial genes. The feasibility of this procedure was demonstrated by using the tetA gene of Tn10, which is lethal when in multiple copies in the presence of 25 micrograms of tetracycline per ml.

Cloning, Molecular↗
PubMed1987

Cloning of genes that suppress an Escherichia coli K-12 alanine auxotroph when present in multicopy plasmids.

To facilitate molecular analyses of a previously uncharacterized gene involved in alanine synthesis, attempts were made to clone the wild-type allele of this gene, alaA, with a mini-Mu plasmid element used for in vivo cloning. Seventy-six independent Ala+ plasmids were isolated and characterized. Physiological, enzymological, and restriction endonuclease analyses indicated that three different genes, none of them alaA, were cloned. These genes were avtA+, which encodes the alanine-valine transaminase (transaminase C); tyrB+, which encodes the tyrosine-repressible transaminase (transaminase D); and a previously undescribed gene, called alaB, which encodes an alanine-glutamate transaminase.

Alanine↗
PubMed1987

Cloning and characterization of the Escherichia coli K-12 alanine-valine transaminase (avtA) gene.

avtA, which encodes the alanine-valine transaminase, transaminase C, was cloned in vivo with high- and low-copy-number mini-Mu cloning vectors. The phenotype conferred by the cloned avtA+ gene usually depended upon the plasmid copy number; most high-copy-number avtA+ plasmids permitted isoleucine-requiring ilvE strains to grow in the absence of isoleucine (multicopy suppression), while low-copy-number avtA+ plasmids did not. avtA was mapped to a 1.25-kilobase segment by comparison of the restriction maps of 24 independent mini-Mu plasmids and then by gamma-delta (Tn1000) mutagenesis of a pBR322-avtA+ plasmid. The direction of transcription of avtA on the cloned fragment was determined with fusions to a promoterless lac gene.

Chromosome Mapping↗
PubMed1985

beta-Chloro-L-alanine inhibition of the Escherichia coli alanine-valine transaminase.

beta-Chloro-L-alanine, an amino acid analog which inhibits a number of enzymes, reversibly inhibited the Escherichia coli K-12 alanine-valine transaminase, transaminase C. This inhibition, along with the inhibition of transaminase B, accounted for the isoleucine-plus-valine requirement of E. coli in the presence of beta-chloro-L-alanine.

Alanine↗