Biomedical subjects

M Ouyang

Publications and source records attributed to M Ouyang.

10 recordsLinked to original sources

PubMed2003

Total synthesis of human and rat coupling factor-6 amide and pressor effects in the rat.

Mitochondrial coupling factor-6 (CF-6) is a component of the ATP synthase complex essential for energy transduction. CF-6, which is localized to the surface of endothelial cells (ECs) and released by shear stress, has been implicated as an endogenous vasoconstrictor. Previous methods of obtaining CF-6 through purification and recombinant methods were laborious and inefficient. Here, we describe the chemical synthesis of human CF-6, (33-108)-NH(2), its C-terminal fragment (55-108)-NH(2), which is termed pCF-6; the rat CF-6, (33-108)-NH(2), its C-terminal fragment pCF-6, (55-108)-NH(2); and two N-terminal fragments of the rat pro-coupling factor-6, (24-52)-NH(2) and (33-52)-NH(2). Biological activities of each peptide were initially screened with bioassays and verified by in vivo studies. Accordingly, intravenous administration of CF-6, pCF-6, rat CF-6, and rat pCF-6 produced a modest but statistically significant increase in blood pressure and heart rate in urethane anesthetized rats, whereas the N-terminal rat pro-coupling factor-6, (24-52)-NH(2) and (33-52)-NH(2) caused no significant pressor response. Thus, the biologically active site probably resides at the C-terminal portion of CF-6 peptides.

Amino Acid Sequence↗

PubMed2003

Environmental, dietary, demographic, and activity variables associated with biomarkers of exposure for benzene and lead.

Classification and regression tree methods represent a potentially powerful means of identifying patterns in exposure data that may otherwise be overlooked. Here, regression tree models are developed to identify associations between blood concentrations of benzene and lead and over 300 variables of disparate type (numerical and categorical), often with observations that are missing or below the quantitation limit. Benzene and lead are selected from among all the environmental agents measured in the NHEXAS Region V study because they are ubiquitous, and they serve as paradigms for volatile organic compounds (VOCs) and heavy metals, two classes of environmental agents that have very different properties. Two sets of regression models were developed. In the first set, only environmental and dietary measurements were employed as predictor variables, while in the second set these were supplemented with demographic and time-activity data. In both sets of regression models, the predictor variables were regressed on the blood concentrations of the environmental agents. Jack-knife cross-validation was employed to detect overfitting of the models to the data. Blood concentrations of benzene were found to be associated with: (a) indoor air concentrations of benzene; (b) the duration of time spent indoors with someone who was smoking; and (c) the number of cigarettes smoked by the subject. All these associations suggest that tobacco smoke is a major source of exposure to benzene. Blood concentrations of lead were found to be associated with: (a) house dust concentrations of lead; (b) the duration of time spent working in a closed workshop; and (c) the year in which the subject moved into the residence. An unexpected finding was that the regression trees identified time-activity data as better predictors of the blood concentrations than the measurements in environmental and dietary media.

Activities of Daily Living↗

PubMed2003

Postnatal maturational changes in rat pelvic autonomic ganglion cells: a mixture of steroid-dependent and -independent effects.

Androgens have potent effects on the maturation and maintenance of a number of neural pathways involved in reproductive behaviors in males. Most studies in this area have focused on central pathways, but androgen receptors are expressed by many peripheral neurons innervating reproductive organs, and previous studies have demonstrated structural and chemical changes in these neurons at puberty and after castration. We have performed the first electrophysiological comparison of pelvic autonomic ganglion neurons in male rats before and after puberty and following pre- or postpubertal castration. Studies were performed in vitro on intact ganglia with hypogastric and pelvic nerves attached to allow synaptic activation of sympathetic or parasympathetic neurons, respectively. Pelvic ganglion neurons underwent many changes in their passive and active membrane properties over the pubertal period, and some of these changes were dependent on exposure to circulating androgens. The most pronounced steroid-dependent effects were on membrane capacitance (soma size) in sympathetic neurons and duration of the action potential afterhyperpolarization in tonic neurons. Our study also showed that rat pelvic ganglion cells and their synaptic inputs were more diverse than previously reported. In conclusion, this study demonstrated that rat pelvic ganglion neurons undergo considerable postnatal changes in their electrophysiological properties. The steroid dependence of some of these changes indicates that circulating androgens may influence reproductive behaviors at many locations within the nervous system not just in the brain and spinal cord.

Age Factors↗

PubMed2001

Energy gaps in "metallic" single-walled carbon nanotubes.

Metallic single-walled carbon nanotubes have been proposed to be good one-dimensional conductors. However, the finite curvature of the graphene sheet that forms the nanotubes and the broken symmetry due to the local environment may modify their electronic properties. We used low-temperature atomically resolved scanning tunneling microscopy to investigate zigzag and armchair nanotubes, both thought to be metallic. "Metallic" zigzag nanotubes were found to have energy gaps with magnitudes that depend inversely on the square of the tube radius, whereas isolated armchair tubes do not have energy gaps. Additionally, armchair nanotubes packed in bundles have pseudogaps, which exhibit an inverse dependence on tube radius. These observed energy gaps suggest that most "metallic" single-walled nanotubes are not true metals, and they have implications for our understanding of the electronic properties and potential applications of carbon nanotubes.

Journal Article↗

PubMed2001

Atomically resolved single-walled carbon nanotube intramolecular junctions.

Intramolecular junctions in single-walled carbon nanotubes are potentially ideal structures for building robust, molecular-scale electronics but have only been studied theoretically at the atomic level. Scanning tunneling microscopy was used to determine the atomic structure and electronic properties of such junctions in single-walled nanotube samples. Metal-semiconductor junctions are found to exhibit an electronically sharp interface without localized junction states, whereas a more diffuse interface and low-energy states are found in metal-metal junctions. Tight-binding calculations for models based on observed atomic structures show good agreement with spectroscopy and provide insight into the topological defects forming intramolecular junctions. These studies have important implications for applications of present materials and provide a means for assessing efforts designed to tailor intramolecular junctions for nanoelectronics.

Journal Article↗

PubMed2000

Dexamethasone attenuates the depressor response induced by neuropeptide Y microinjected into the nucleus tractus solitarius in rats.

An investigation was made of the effect of dexamethasone (Dex) injection into the nucleus tractus solitarius (NTS) on the cardiovascular response to neuropeptide Y in rats. Dex (39 pmol) injected into the NTS inhibited the hypotension and bradycardia caused by NPY (5 pmol) with a short latency (10 min) and a long duration of action (up to 4 h). The rapid inhibition by Dex (39 pmol) of the cardiovascular response to NPY was not blocked by pretreatment with the glucocorticoid receptor blocker, RU38486 (47 or 117 pmol respectively), but was reversed by bicuculline (30 pmol). Microiontophoresis of NPY (0.01 mM, pH 6.5) into the NTS increased the spontaneous firing of the majority (68.4%) of baroreflex-excited cells, but decreased the firing of most (73.7%) baroreflex-inhibited cells. In contrast, Dex (0.02 M, pH 6.5) decreased the spontaneous firing of the majority of baroreflex-excited cells (42.1% of normal response) and decreased the inhibition of baroreflex-inhibited cells (47.5% of normal response). The responses of the majority of baroreceptive cells to NPY were blocked by iontophoretic administration of Dex. Dex (200 microM) increased the delayed rectifier outward K+ current by 31.4+/-1.1% (n=5), whereas NPY alone, at a concentration of 1.5 microM, inhibited the current by 28.6+/-0.8% (n=5). In the presence of Dex (200 microM), addition of NPY (1.5 microM) had no effect on the current. In conclusion, NTS-administered-Dex attenuated the cardiovascular response to NPY injected into the same area via a rapid membrane effect, which was mediated by an action on GABA(A) receptors and on the delayed rectifier outward K(+) channel.

Animals↗

PubMed1996

[Effects of different lowdoses of aspirin on platelet activation and the number of platelets in the patients with coronary heart disease].

The number of alpha-granule membrane protein 140 (GMP-140) molecules was detected by using specific monoclonal antibodies (125I-SZ-51) against GMP-140 in three groups of patients with unstable angina treated with aspirin 50 mg (n = 27), 150 mg (n = 26) and 300 mg (n = 30) a day before and 7 days after treatment. The number of platelets was counted by using the routine method. The results indicated that the number of GMP-140 molecules decreased significantly and the number of platelets increased significantly after treatment with aspirin. With the increase of aspirin dosage the degree of these two changes increased (P < 0.01, both) too. When 300 mg of aspirin was used, the number of GMP-140 molecules was lower than that in a control group of healthy subjects (P < 0.005) and the number of platelets reached that of the control group (P > 0.05). There was no difference on the immediate side effects when these three dosages of aspirin were used. The authors of the opinion are that it is rational to use 300 mg of aspirin to treat patients with unstable angina at the beginning.

Aged↗

PubMed1994

[Recurrent astrocytoma versus primary astrocytoma: a comparative study of morphological changes of 32 cases].

The pathologic morphological changes of 32 cases of recurrent astrocytoma (RA) and primary astrocytoma were reported. During recurrence, 20 cases (62.5%) of astrocytomas transformed into cases at higher grades. Twelve cases remained at the same grades as primary tumors. Among 21 cases of RA at grades III and IV, 15 cases (71.4%) came from primary astrocytomas, grades I and II. The change from astrocytoma grade I to grade III or IV took time longer than that from grade II to grade III or IV. The recurrent time of astrocytomas with different grades showed no statistical differences. Postoperative radiotherapy/chemotherapy did not play a major role in grading changes and recurrent time.

Adult↗

PubMedDate not supplied

Controlled template-assisted assembly of plasmid DNA into nanometric particles with high DNA concentration.

A series of novel cationic detergents that contain cleavable hydrophilic isothiuronium headgroups was synthesized, and their utility in controlled assembly of plasmid DNA into small stable particles with high DNA concentration investigated. The detergents have alkyl chains of C(8)-C(12) and contain hydrophilic isothiuronium headgroups that give relatively high critical micelle concentration (CMC) to the detergents (>10 mM). The isothiuronium group masks a sulfhydryl group on the detergent and can be cleaved in a controlled manner under basic conditions to generate a reactive thiol group. The thiol group can undergo a further reaction after the detergents have accumulated on a DNA template to form a disulfide-linked lipid containing two alkyl chains. The pH-dependent kinetics of cleavage of the isothiuronium group, the CMC of the surfactants, the formation of the complexes, and the transfection efficiency of the DNA complexes have been investigated. Using the C(12) detergent, a approximately 6 kilo-basepair plasmid DNA was compacted into a small particle with an average diameter of around 40 nm with a approximately -13 mV zeta-potential at high DNA concentration (up to 0.3 mg/mL). The compounds were well tolerated in cell culture and showed no cytotoxicity under their CMCs. Under appropriate conditions, the small particle retained transfection activity.

Animals↗

PubMedDate not supplied

Different mechanisms for [Ca2+]i oscillations induced by carbachol and high concentrations of [Ca2+]o in the rat ventricular myocyte.

1. The purpose of the present study was to explore the different mechanisms of [Ca2+]i oscillations induced by high concentrations of either carbachol (CCh) or extracellular Ca2+ ([Ca2+]o). First, we compared the oscillations induced by CCh at concentrations of 100-300 micromol/L and [Ca2+]o (5 mmol/L) in the single rat ventricular myocyte. Second, we studied CCh- and [Ca2+]o-induced [Ca2+]i oscillations following either interference with the production of inositol trisphosphate (IP3), reductions in cytosolic Ca2+ ([Ca2+]i), inhibition of Ca2+ influx and Na+-Ca2+ exchange or depletion of Ca2+ from its intracellular store. 2. The [Ca2+]i oscillations induced by CCh were frequent and were superimposed on [Ca2+]i transients in electrically stimulated cells, whereas those induced by high [Ca2+]o were occasional and occurred in quiescent cells and between [Ca2+]i transients in electrically stimulated cells. In both cases, [Ca2+]i oscillations were preceded by an increase in resting levels of [Ca2+]i. 3. Carbachol-induced [Ca2+]i oscillations were accompanied by an increase in amplitude and prolongation of the time of decline to 80% of the peak of the [Ca2+]i transient, while high [Ca2+]o-induced [Ca2+]i oscillations were the opposite. 4. A reduction of [Ca2+]o to 0.1 mmol/L and treatment with Ni2+ or ryanodine or 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid AM (BAPTA-AM) abolished the [Ca2+]i oscillations induced by both CCh and high [Ca2+]o. 5. The calcium channel blockers verapamil and nifedipine and inhibitors of phospholipase C (neomycin and U-73122) abolished the [Ca2+]i oscillations induced by CCh; Li+ accelerated the onset of the [Ca2+]i oscillations induced by CCh. 6. These observations suggest that the mechanisms responsible for the [Ca2+]i oscillations induced by CCh and high [Ca2+]o are different from each other. Other than an increase in extracellular Ca2+ influx as a mechanism common for both CCh- and high [Ca2+]o-induced [Ca2+]i oscillations, the CCh-induced [Ca2+]i oscillations involve influx of Ca2+ via L-type Ca2+ channels, Na+-Ca2+ exchange, mobilization of intracellular Ca2+ and IP3 production.

Animals↗