Search PubMed⌕ Search

Biomedical subjects

K Wang

Publications and source records attributed to K Wang.

At least 469 records · Page 26Linked to original sources
PubMed1993

Organization of the murine T-cell receptor gamma locus.

Murine T cells carry either of two antigen receptors on their surface: alpha beta or gamma delta T-cell receptors (TCR). The function of gamma delta T cells is not well understood. In this population, subsets exist with tissue-specific localization, with invariant variable regions, and with specificity for self antigens. We have analyzed the murine TCR gamma locus by field inversion gel electrophoresis and cosmid cloning. The structure of the complete TCR gamma locus, the first complete physical map of any mouse TCR locus, is reported here. The locus spans 205 kb and consists of four clusters of genes and gene segments. Each cluster contains one or more variable elements, one joining element, and one constant element. We demonstrate that the C gamma 4 gene is distinguished from the other C gamma genes in that it has an additional hinge-encoding exon. New enhancer-like elements are identified in two of the clusters, downstream from the C gamma genes. The most upstream cluster has four V elements and resembles the human TCR gamma locus. The four clusters probably arose via duplications.

Animals↗
PubMed1993

Sequence and genomic organization of Norwalk virus.

A library of overlapping cDNAs obtained from Norwalk virus purified from stools of human volunteers (Jiang et al., 1990, Science 250, 1580-1583) was used to obtain the nucleotide sequence of the viral genome. The sequence has a total of 7642 nucleotides, excluding the 3' poly(A) tail, and has a base composition of 48% G + C. Three open reading frames (ORF) are predicted in the sequence. The longest ORF (ORF1, nucleotides (nt) 146 to 5359) is predicted to encode a polyprotein precursor to nonstructural proteins based on identification of sequences similar to the picornavirus 2C protein, 3C protease, and 3D RNA-dependent RNA polymerase. ORF2 (nt 5346 to 6935) is predicted to encode a polypeptide with a predicted molecular weight of 56,571 (56.6K, close to the expected size of the viral capsid protein), and it contains a short region of sequence similarity to the picornavirus structural protein VP3. A third potential ORF (nt 6938 to 7573) could encode a small polypeptide of 22.5K. The genomic organization found in Norwalk virus shares striking similarities with the genome of two caliciviruses, the feline calicivirus and the rabbit hemorrhagic disease virus. The morphology, size, polarity, and genomic organization of the Norwalk virus indicate it is a member of the Caliciviridae family.

Base Sequence↗
PubMed1993

Redistribution of hepatocyte chloride during L-alanine uptake.

We used ion-sensitive, double-barrel microelectrodes to measure changes in hepatocyte transmembrane potential (Vm), intracellular K+, Cl-, and Na+ activities (aiK, aiCl and aiNa), and water volume during L-alanine uptake. Mouse liver slices were superfused with control and experimental Krebs physiological salt solutions. The experimental solution contained 20 mM L-alanine, and the control solution was adjusted to the same osmolality (305 mOsm) with added sucrose. Hepatocytes also were loaded with 50 mM tetramethylammonium ion (TMA+) for 10 min. Changes in cell water volume during L-alanine uptake were determined by changes in intracellular, steady-state TMA+ activity measured with the K+ electrode. Hepatocyte control Vm was -33 +/- 1 mV. L-alanine uptake first depolarized Vm by 2 +/- 0.2 mV and then hyperpolarized Vm by 5 mV to -38 +/- 1 mV (n = 16) over 6 to 13 min. During this hyperpolarization, aiNa increased by 30% from 19 +/- 2 to 25 +/- 3 mM (P < 0.01), and aiK did not change significantly from 83 +/- 3 mM. However, with added ouabain (1 mM) L-alanine caused only a 2-mV increase in Vm, but now aiK decreased from 61 +/- 3 to 54 +/- 5 mM (P < 0.05). Hyperpolarization of Vm by L-alanine uptake also resulted in a 38% decrease of aiCl from 20 +/- 2 to 12 +/- 3 mM (P < 0.001). Changes in Vm and VCl-Vm voltage traces were parallel during the time of L-alanine hyperpolarization, which is consistent with passive distribution of intracellular Cl- with the Vm in hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine↗
PubMed1993

Hepatocyte water volume and potassium activity during hypotonic stress.

Hepatocytes exhibit a regulatory volume decrease (RVD) during hypotonic shock, which comprises loss of intracellular K+ and Cl- accompanied by hyperpolarization of transmembrane potential (Vm) due to an increase in membrane K+ conductance, (GK). To examine hepatocyte K+ homeostasis during RVD, double-barrel, K+-selective microelectrodes were used to measure changes in steady-state intracellular K+ activity (aKi) and Vm during hyposmotic stress. Cell water volume change was evaluated by measuring changes in intracellular tetramethylammonium (TMA+). Liver slices were superfused with modified Krebs physiological salt solution. Hyposmolality (0.8 x 300 mosm) was created by a 50 mM step-decrease of external sucrose concentration. Hepatocyte Vm hyperpolarized by 19 mV from -27 +/- 1 to -46 +/- 1 mV and aiK decreased by 14% from 91 +/- 4 to 78 +/- 4 mM when slices were exposed to hyposmotic stress for 4-5 min. Both Vm and aKi returned to control level after restoring isosmotic solution. In paired measurements, hypotonic stress induced similar changes in Vm and aKi in both control and added ouabain (1 mM) conditions, and these values returned to their control level after the osmotic stress. In another paired measurement, hypotonic shock first induced an 18-mV increase in Vm and a 15% decrease in aKi in control condition. After loading hepatocytes with TMA+, the same hypotonic shock induced a 14-mV increase in Vm and a 14% decrease in aTMAi. This accounted for a 17% increase of intracellular water volume, which was identical to the cell water volume change obtained when aKi was used as the marker.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Nebulin is a full-length template of actin filaments in the skeletal muscle sarcomere: an immunoelectron microscopic study of its orientation and span with site-specific monoclonal antibodies.

Nebulin, a giant myofibrillar protein with size variants from 700 to 900 kDa in various skeletal muscles, has been proposed to constitute a set of inextensible filaments anchored at the Z-line and coextensive with actin filaments. To elucidate the architectural organization of this fourth set of myofilaments in the skeletal muscle sarcomere, we performed immunoelectron microscopic localization of epitope profiles of a number of site-specific monoclonal antibodies against cloned human nebulin fragments of known sequence loci. Monoclonal antibody N113, which is directed to fragment ND8 at approximately 300 residues away from the C-terminus, labelled the edges of Z-lines in both human quadriceps muscle and rabbit psoas muscle. Monoclonal antibody N101, which is directed to fragment NB5 near the N-terminal side, is localized to a single locus at 0.89 micron from the Z-line in human quadriceps muscle and 0.80 micron from the Z-line in rabbit psoas muscle. Additionally, monoclonal antibody N109, which is directed to fragment NA3 on the carboxy side of the adjacent fragment NB5, is localized at 0.76 micron away from the Z-line in rabbit psoas muscle. This one-to-one correspondence between epitope loci and sequence loci demonstrates that a single nebulin polypeptide spans the length of the thin filament with its C-terminus anchored at the Z-line. The epitope spacings of site-specific antibodies are consistent with the notion that the nebulin filament is uniform in mass density along its length.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1993

Primary structure of Beijing duck apolipoprotein A-1.

The primary structure of Beijing duck apolipoprotein A-1 was determined by sequencing peptide fragments derived from tryptic and endoproteinase Asp-N digestion of the protein, and alignment with homologous chicken apo A-1. All of the peptide fragments were isolated by high-pressure liquid chromatography (HPLC) with a Vydac C18 column using a trifluoroacetic acid (TFA) buffer system. The N-terminus of the protein was determined to be aspartic acid by directly sequencing 52 residues of the intact protein. The C-terminus was alanine. The protein contains 240 amino acid residues. By analysis of the whole protein and its tryptic peptides, a six amino acid (Arg-Tyr-Phe-Trp-Gln-His) prosegment was determined. No cross-reactivity between duck and human apo A-1 with a goat antiserum against human apo A-1 was found. Sequence analysis of apo A-1 of other species indicates that amino acid substitutions in rat are more extensive than in other mammals. Isoleucine residues in apo A-1 are inversely correlated to the homology of human to other species, except dog.

Amino Acid Sequence↗
PubMed1993

Stimulation of drinking by bacterial endotoxins in the rat.

We investigated the effects of endotoxins on water balance, rectal temperature, and food intake in male Long-Evans rats with femoral venous catheters. Extracts of Escherichia coli or Salmonella minnesota, in doses ranging from 125 to 500 micrograms/kg IV, stimulated drinking and reduced urinary water loss for several hours. The net gain of 5 ml water 2 h after the lowest dose of E. coli endotoxin was sufficient to reduce plasma osmolality and sodium concentration 2 to 3%. Drinking occurred during the period of hypothermia that frequently precedes the onset of endotoxin-induced fever, so cannot be attributed to increased body temperature. Doses of endotoxin causing drinking inhibited both spontaneous and deprivation-induced feeding. The cause of the drinking is not known, but may involve mechanisms other than the known dehydrational signals controlling thirst.

Animals↗
PubMed1993

The ozonation of cholesterol: separation and identification of 2,4-dinitrophenylhydrazine derivatization products of 3 beta-hydroxy-5-oxo-5,6-secocholestan-6-al.

The ozonation products of cholesterol, which are of interest as possible biomarkers of O3 exposure, were studied by derivatization with 2,4-dinitrophenylhydrazine (DNPH). The DNPH derivatization of 3 beta-hydroxy-5-oxo-5,6-secocholestan-6-al (2) produces the expected trans (3b) and cis (3c) derivatives of 3 beta-hydroxy-5-oxo-5,6-secocholestan-6-al, and the unexpected DNPH derivative of 3,5-dihydroxy-B-norcholestane-6-carboxaldehyde (3a). The structures of 3a, 3b, and 3c were identified with 1H nuclear magnetic resonance (NMR), 13C NMR, DEPT, COSY, and H-C correlation two-dimensional NMR techniques, and by comparison with the spectra of known compounds. A possible mechanism involving an enamine functionality is proposed for the formation of 3a. The ratio of 3a/(3b + 3c) depends on the concentration of acid used and the reaction time.

Cholestanones↗
PubMed1993

Passive tension and stiffness of vertebrate skeletal and insect flight muscles: the contribution of weak cross-bridges and elastic filaments.

Tension and dynamic stiffness of passive rabbit psoas, rabbit semitendinosus, and waterbug indirect flight muscles were investigated to study the contribution of weak-binding cross-bridges and elastic filaments (titin and minititin) to the passive mechanical behavior of these muscles. Experimentally, a functional dissection of the relative contribution of actomyosin cross-bridges and titin and minititin was achieved by 1) comparing mechanically skinned muscle fibers before and after selective removal of actin filaments with a noncalcium-requiring gelsolin fragment (FX-45), and 2) studying passive tension and stiffness as a function of sarcomere length, ionic strength, temperature, and the inhibitory effect of a carboxyl-terminal fragment of smooth muscle caldesmon. Our data show that weak bridges exist in both rabbit skeletal muscle and insect flight muscle at physiological ionic strength and room temperature. In rabbit psoas fibers, weak bridge stiffness appears to vary with both thin-thick filament overlap and with the magnitude of passive tension. Plots of passive tension versus passive stiffness are multiphasic and strikingly similar for these three muscles of distinct sarcomere proportions and elastic proteins. The tension-stiffness plot appears to be a powerful tool in discerning changes in the mechanical behavior of the elastic filaments. The stress-strain and stiffness-strain curves of all three muscles can be merged into one, by normalizing strain rate and strain amplitude of the extensible segment of titin and minititin, further supporting the segmental extension model of resting tension development.

Actins↗
PubMed1993

Viscoelasticity of the sarcomere matrix of skeletal muscles. The titin-myosin composite filament is a dual-stage molecular spring.

The mechanical roles of sarcomere-associated cytoskeletal lattices were investigated by studying the resting tension-sarcomere length curves of mechanically skinned rabbit psoas muscle fibers over a wide range of sarcomere strain. Correlative immunoelectron microscopy of the elastic titin filaments of the endosarcomeric lattice revealed biphasic extensibility behaviors and provided a structural interpretation of the multiphasic tension-length curves. We propose that the reversible change of contour length of the extensible segment of titin between the Z line and the end of thick filaments underlies the exponential rise of resting tension. At and beyond an elastic limit near 3.8 microns, a portion of the anchored titin segment that adheres to thick filaments is released from the distal ends of thick filament. This increase in extensible length of titin results in a net length increase in the unstrained extensible segment, thereby lowering the stiffness of the fiber, lengthening the slack sarcomere length, and shifting the yield point in postyield sarcomeres. Thus, the titin-myosin composite filament behaves as a dual-stage molecular spring, consisting of an elastic connector segment for normal response and a longer latent segment that is recruited at and beyond the elastic limit of the sarcomere. Exosarcomeric intermediate filaments contribute to resting tension only above 4.5 microns. We conclude that the interlinked endo- and exosarcomeric lattices are both viscoelastic force-bearing elements. These distinct cytoskeletal lattices appear to operate over two ranges of sarcomere strains and collectively enable myofibrils to respond viscoelastically over a broad range of sarcomere and fiber lengths.

Animals↗
PubMed1993

Interplay between passive tension and strong and weak binding cross-bridges in insect indirect flight muscle. A functional dissection by gelsolin-mediated thin filament removal.

The interplay between passive and active mechanical properties of indirect flight muscle of the waterbug (Lethocerus) was investigated. A functional dissection of the relative contribution of cross-bridges, actin filaments, and C filaments to tension and stiffness of passive, activated, and rigor fibers was carried out by comparing mechanical properties at different ionic strengths of sarcomeres with and without thin filaments. Selective thin filament removal was accomplished by treatment with the actin-severving protein gelsolin. Thin filament, removal had no effect on passive tension, indicating that the C filament and the actin filament are mechanically independent and that passive tension is developed by the C filament in response to sarcomere stretch. Passive tension increased steeply with sarcomere length until an elastic limit was reached at only 6-7% sarcomere extension, which corresponds to an extension of 350% of the C filament. The passive tension-length relation of insect flight muscle was analyzed using a segmental extension model of passive tension development (Wang, K, R. McCarter, J. Wright, B. Jennate, and R Ramirez-Mitchell. 1991. Proc. Natl. Acad. Sci. USA. 88:7101-7109). Thin filament removal greatly depressed high frequency passive stiffness (2.2 kHz) and eliminated the ionic strength sensitivity of passive stiffness. It is likely that the passive stiffness component that is removed by gelsolin is derived from weak-binding cross-bridges, while the component that remains is derived from the C filament. Our results indicate that a significant number of weak-binding cross-bridges exist in passive insect muscle at room temperature and at an ionic strength of 195 mM. Analysis of rigor muscle indicated that while rigor tension is entirely actin based, rigor stiffness contains a component that resists gelsolin treatment and is therefore likely to be C filament based. Active tension and active stiffness of unextracted fibers were directly proportional to passive tension before activation. Similarly, passive stiffness due to weak bridges also increased linearly with passive tension, up to a limit. These correlations lead us to propose a stress-activation model for insect flight muscle in which passive tension is a prerequisite for the formation of both weak-binding and strong-binding cross-bridges.

Actins↗
PubMed1993

Sulfate conjugates of iodothyronines in developing sheep: effect of fetal hypothyroidism.

We recently showed that thyroxine sulfate (T4S) and 3,3',5-triiodothyronine sulfate (T3S) were major thyroid hormone metabolites in ovine fetuses and neonates. To further characterize the sulfation pathway in ovine fetuses, we measured 3,3',5'-triiodothyronine (rT3S) in serum and other body fluids in samples obtained from fetal (n = 23, 94-145 days of gestational age, term = 150 days), newborn (n = 6), and adult (n = 6) sheep. In addition, T3S, T4S, and rT3S levels were measured in tissue fluids and serum samples obtained from ovine fetuses 13 days after total thyroidectomy (Tx) conducted at gestational age of 110-113 days (n = 5). Sham-operated twin fetuses served as controls (n = 5). The relative order of mean rT3S concentration for various tissue fluids in fetuses were meconium > bile > serum > allantoic fluid > urine or amniotic fluid. Peak mean tissue fluid levels generally occurred at 110-130 days gestation. In hypothyroid fetuses, significant decreases in the mean serum concentrations of T4S and rT3S, but not T3S, were noted. The mean rT3S level also was decreased significantly in allantoic fluid, bile, and meconium, whereas T4S and T3S levels were reduced only in bile of the Tx fetuses. These data demonstrate that sulfation is a major pathway in thyroid hormone metabolism in both euthyroid and hypothyroid ovine fetuses.

Animals↗
PubMed1993

Endotoxin stimulates drinking in rats without changing dehydrational signals controlling thirst.

Intravenous injections of endotoxins from Escherichia coli or Salmonella minnesota stimulate drinking and reduce urinary excretion of water and solutes in rats. E. coli endotoxin (0.15 or 0.45 mg/kg i.v.) stimulated drinking without increasing plasma osmolality or sodium concentration, hematocrit, blood hemoglobin, or plasma protein concentration and without decreasing arterial pressure. Similarly, a dipsogenic dose of S. minnesota endotoxin (0.25 mg/kg i.v.) did not reduce arterial or venous pressures or change heart rate. Blocking the renin-angiotensin system with captopril or blocking histamine receptors with pyrilamine and cimetidine did not reduce drinking or urinary fluid retention caused by E. coli endotoxin. Injections of 10 or 450 ng E. coli endotoxin into a lateral cerebral ventricle increased body temperature but not water intake. In contrast to its stimulatory effect in water-replete rats, E. coli endotoxin (0.45 mg/kg i.v.) inhibited drinking in 24-h water-deprived rats. Thus we find no evidence to support the hypothesis that endotoxin causes thirst by changing known physiological signals of cellular or extracellular dehydration. The mechanism remains unknown.

Animals↗
PubMed1993

Intestinal expression of the human apoA-I gene in transgenic mice is controlled by a DNA region 3' to the gene in the promoter of the adjacent convergently transcribed apoC-III gene.

The apoA-I gene in humans is principally expressed in liver and small intestine. Using transgenic mice, we previously showed that 256 bp of 5' flanking DNA was sufficient for liver expression, but as much as 5.5 kb of 5' and 4.0 kb of 3' DNA did not allow intestinal expression of the human apoA-I transgene. In the current study, a 10.5 kb DNA construction containing the apoA-I and the adjacent convergently transcribed apoC-III genes, which extends from 300 bp 5' to the apoA-I gene to 2.5 kb 5' to the apoC-III gene, produced high levels of apoA-I intestinal expression. A similar DNA construction ending 1.4 kb 5' to the apoC-III gene also allowed apoA-I intestinal expression. The DNA region from 0.2 to 1.4 kb 5' to the apoC-III gene was then cloned 1.7 kb 3' to the apoA-I gene in both orientations in the absence of apoC-III gene sequences. Intestinal apoA-I expression was also achieved with both of these constructions. In summary, these in vivo experiments suggest that the intestinal control region for the apoA-I gene is distinct from the liver control region, resides 3' to the gene in the promoter of the adjacent apoC-III gene, and has some properties of a tissue-specific enhancer.

Animals↗
PubMed1992

Sensitive micromethod for column liquid chromatographic determination of fluoxetine and norfluoxetine in human plasma.

A rapid, selective and sensitive micromethod has been developed for the determination of fluoxetine (FLU) and its demethylated metabolite norfluoxetine (N-FLU) using a 250-microliters plasma sample and column liquid chromatography with ultraviolet detection at 226 nm. The limit of detection is 2.0 ng/ml for both FLU and N-FLU. Peak-height ratios are linear over a concentration range of 10-800 and 10-1000 ng/ml for FLU and N-FLU, respectively. Acceptable coefficients of variation are demonstrated for both within-run and day-to-day assays. Selected drugs were checked for interference. The method, which requires a very small volume of plasma, is sensitive enough for pharmacokinetic studies in animals, clinical pharmacology studies and drug monitoring in children or adult patients.

Chromatography, Liquid↗
PubMed1992

The premature ventricular complex as a diagnostic aid.

Premature ventricular complexes (PVCs) can provide clues to the physical or electrocardiographic diagnosis through the associated compensatory pause, the break in the regularity of the rhythm, or the morphology of the PVC itself. A PVC may allow visualization of the P wave or of atrial flutter waves that would otherwise be obscured in the electrocardiogram. It can also be useful in distinguishing an S3 gallop from an S4 gallop. The compensatory pause that follows a PVC may allow normal conduction of the next QRS complex in a patient with a rate-dependent intraventricular conduction defect, and this normalized QRS complex may contain important diagnostic findings. A PVC can also reveal a myocardial infarct pattern when the sinus complex fails to do so. Although the need to treat PVCs is currently being de-emphasized, their diagnostic utility should not be overlooked.

Atrial Flutter↗
PubMed1992

Cholesterol ozonation products as biomarkers for ozone exposure in rats.

Cholesterol, 1, which is present in both the lung lining fluid and cell membranes of lung tissue, reacts with ozone in aqueous systems to give 3 beta-hydroxy-5-oxo-5,6-secocholestan-6-al (2) as the major product. Reaction of 2 with 2,4-dinitrophenyl hydrazine (DNPH) in aqueous solutions, liposomes or lung extracts affords the anti and syn DNPH derivatives of 2 (3b and 3c) and of the rearrangement product 3,5-dihydroxy-B-norcholestane-6-carboxaldehyde (3a). These derivatives also are detected in lung tissue extracts from rats exposed to 1.3 ppm ozone for 12 hr.

1,2-Dipalmitoylphosphatidylcholine↗