PubMed Health⌕ Search

Biomedical subjects

R Wang

Publications and source records attributed to R Wang.

At least 649 records · Page 36Linked to original sources
PubMed1991

Secretion of the beta/A4 amyloid precursor protein. Identification of a cleavage site in cultured mammalian cells.

Alzheimer's disease, a progressive neurodegenerative disorder, affects greater than 10% of the population of individuals greater than 65 years of age. A principal neuropathological feature of this disease is the senile plaque, a fibrillar extracellular deposit primarily composed of a approximately 4-kDa peptide, beta/A4, derived from the amyloid precursor protein (APP). Studies in cultured cells have documented that APP matures through a constitutive secretory pathway and is cleaved at or near the cell surface to release a large ectodomain into the extracellular space. To define the APP cleavage site, we constructed a Chinese hamster ovary cell line, which constitutively overexpresses human APP-770, and analyzed the COOH termini of secreted APP-770-related molecules. Using plasma desorption mass spectrometry and chemical microsequencing, we document that an APP cleavage site in Chinese hamster ovary cells leading to secretion occurs immediately COOH-terminal to lysine residue 687, which lies adjacent to the hydrophobic membrane-spanning domain.

Amino Acid Sequence↗
PubMed1991

Reactivity of medium-chain acyl-CoA dehydrogenase toward molecular oxygen.

The free two-electron-reduced form of medium-chain acyl-CoA dehydrogenase is reoxidized by 120 microM molecular oxygen (50 mM phosphate buffer, pH 7.6, 2 degrees C) with a half-time of approximately 7 s. Reoxidation yields hydrogen peroxide as a major product with only traces of the superoxide anion. In contrast, enzyme reduced with octanoyl-CoA is extremely slowly reoxidized oxygen, and so a series of 14 different substrate analogues have been tested to assess the structural factors responsible for this effect. Complexes with redox-inactive ligands such as 3-thia- and 2-azaoctanoyl-CoA lead to an approximately 3000-fold slowing of the rate of reoxidation of the free dihydroflavin form of the enzyme. Comparable ligands lacking the thioester carbonyl function are much less effective with rates some 1.3-4-fold slower than the free enzyme. The strong suppression of oxygen reactivity observed with certain ligands is probably not simply a steric effect but may reflect desolvation of the active site and consequent destabilization of the superoxide anion intermediate formed during reoxidation of the flavin. The profound differences in oxygen reactivity between acyl-CoA dehydrogenase and acyl-CoA oxidase and the unusual stability of certain flavoprotein semiquinones in air are discussed in terms of these thermodynamic and kinetic arguments.

Acyl-CoA Dehydrogenase↗
PubMed1991

The effects of parathyroid hormone on L-type voltage-dependent calcium channel currents in vascular smooth muscle cells and ventricular myocytes are mediated by a cyclic AMP dependent mechanism.

The present study demonstrated that L channel currents were decreased in smooth muscle cells, and increased in ventricular myocytes by both bovine parathyroid hormone, (bPTH-(1-34)), and dibutyryl cyclic AMP (db-cAMP), using the whole cell version of the patch clamp technique with Ba2+ as the charge carrier. The effects of bPTH-(1-34) and db-cAMP on L channel currents were additive but not synergistic. Furthermore, the effects of bPTH-(1-34) on L channel currents in these 2 cell preparations were abolished in the presence of a cAMP antagonist. These results suggest that the effects of bPTH-(1-34) on L channel currents in vascular smooth muscle cells and ventricular myocytes are mediated by a cAMP-dependent mechanism.

Animals↗
PubMed1991

The reductive half-reaction in acyl-CoA oxidase from Candida tropicalis: interaction with acyl-CoA analogues and an unusual thioesterase activity.

A series of acyl-CoA analogues has been used to probe the substrate binding site and reductive half-reaction of acyl-CoA oxidase from the alkane utilizing yeast Candida tropicalis. Alkyl-SCoA thioethers, from octyl- to hexadecyl-SCoA, bind to the oxidase with progressively larger spectral perturbation of the flavin chromophore and with an incremental binding energy of about 260 cal/methylene group. The hydrocarbon binding subsite for acyl-CoA oxidase appears extensive and only weakly hydrophobic. CoA binding per se appears to contribute about 2.8 kcal to the observed binding energy. A number of acyl-CoA analogues such as 3-thia-acyl-, 3-oxa-acyl-, trans-3-enoyl-, and 3-keto-acyl-CoA derivatives form charge transfer complexes with the oxidase, but these long wavelength bands are both less pronounced and much less stable than those encountered with the acyl-CoA dehydrogenases. This instability reflects an intrinsic thioesterase activity of the oxidase which is observed with those ligands forming enolate to oxidized flavin charge-transfer complexes, but not with normal substrates such as palmitoyl-CoA. Chemical precedent suggests that these enzyme-bound enolates eliminate CoA via a ketene intermediate. The differences in behavior between acyl-CoA oxidase and dehydrogenase toward the ligands used in this work are discussed in terms of the need to exclude oxygen from productive encounters with substrate-reduced dehydrogenase.

Acyl Coenzyme A↗
PubMed1991

Chemical reduction of 3-oxo and unsaturated groups in fatty acids of diphosphoryl lipid A from the lipopolysaccharide of Rhodopseudomonas sphaeroides. Comparison of biological properties before and after reduction.

Unlike the diphosphoryl lipid A (DPLA) derived from toxic lipopolysaccharide of Escherichia coli and Salmonella strains, the DPLA from nontoxic lipopolysaccharide of Rhodopseudomonas sphaeroides ATCC 17023 is biologically inactive. This could be due to the presence of 3-oxotetradecanoic and delta 7-tetradecenoic acids. These two fatty acids in R. sphaeroides DPLA were catalytically reduced in platinum oxide/H2 to the 3-hydroxy and saturated fatty acids, respectively. The biologically active E. coli DPLA was also treated with platinum oxide/H2, but as expected, the reduction step did not change the structure. These two preparations were then compared with the untreated samples for biological activity in three select in vitro assays. Over a range of 0.01-100 ng/ml, both normal and reduced DPLA from R. sphaeroides were inactive in priming phorbol myristate acetate-stimulated superoxide anion release in human alveolar macrophages. Over a range of 10-10(3) ng/ml, both samples failed to induce tumor necrosis factor in the RAW 264.7 murine macrophage cell line. The reduced DPLA marginally activated 70Z/3 pre-B cells at concentrations of 0.1-30 micrograms/ml. In every case, both normal and platinum oxide/H2-treated E. coli DPLA were biologically active. These results indicate that the lack of biological activity of R. sphaeroides DPLA is not due to the presence of 3-oxo and unsaturated fatty acids, but rather to one or more of the following: (i) presence of only five fatty acyl groups (compared to six in active lipid A); (ii) presence of 3-hydroxydecanoic acids (rather than 3-hydroxytetradecanoic, in active lipid A); (iii) greater variation in size of the fatty acids.

Catalysis↗
PubMed1991

Varicocele in the rat: a new experimental model. Effect on histology, ultrastructure and temperature of the testis and the epididymis.

With no consistent animal prototype for the study of varicocele, we set out to create a model in the rat by complete ligation of the main branch of left spermatic vein (MBSV) or by partial ligation of the left renal vein. Three months later, the histology, ultrastructure and temperature of the testis and epididymis were studied. Microscopically, spermatogenic arrest was the most frequent anomaly seen. The most frequently noted ultrastructural change of the testis was distension of smooth endoplasmic reticula in Sertoli cells. The microvilli of columnar epithelia in epididymis were sparse and showed local defects. Lesions and increased temperatures in the testis and epididymis induced by the ligation of the left MBSV were similar to those seen in partial ligation of the left renal veins, with no significant differences between left and right. Significant differences were found, however, on comparison with the controls.

Animals↗
PubMed1991

Isolation and characterization of an established endothelial cell line from transgenic mouse hemangiomas.

A murine endothelial cell line was isolated from hemangiomas induced by expression of the polyoma early region gene in transgenic mice. After two cell sortings using acetylated low-density lipoprotein with a fluorescent label (Dil-Ac-LDL), a pure population of endothelial cells has been carried for more than 60 passages from the animal. The cells retain endothelial cell properties such as a characteristic cobblestone appearance at confluency, contact-inhibited growth, and active uptake of Ac-LDL. Expression analysis shows that the cells express both the polyoma transgene and the von Willebrand factor, an endothelial cell marker. Subcutaneous injection of the cultured endothelial cells into nontransgenic histocompatible mice or nude mice led to hemangioma formation, and endothelial cells were re-isolated by cell sorting from these secondary hemangiomas. This cell line represents a renewable source of murine endothelial cells derived from transgenic mice that can be studied both in vitro and by reintroduction into a host.

Animals↗
PubMed1991

Platelet-activating factor stimulates motion parameters of cryopreserved human sperm.

Platelet-activating factor is a naturally occurring molecule that does not appear to cause the detrimental effects to sperm as have been reported for other synthetic stimulatory agents. Incubation of freeze-thawed sperm with low motility with PAF at concentrations greater than or equal to 1.0 microM significantly improved a number of motion parameters (% motility, VSL and LIN). Optimal incubation conditions for PAF were defined at 1 hour and at 25 degrees C. The success of assisted reproductive techniques employing cryopreserved sperm with poor motility may be enhanced by stimulation protocols employing PAF.

Cryopreservation↗
PubMed1991

Two types of voltage-dependent calcium channel currents and their modulation by parathyroid hormone in neonatal rat ventricular cells.

The positive inotropic and chronotropic actions of parathyroid hormone (PTH) in cardiac cells are considered to be related to the modulation of calcium influx. The underlying mechanisms, however, are unknown, and direct electrophysiological evidence at the single-cell level is required. In the present study, the whole-cell configuration of the patch-clamp technique was used in neonatal rat ventricular cells to identify both transient (T) and long-lasting (L) voltage-dependent calcium channels according to their electrophysiological and pharmacological characteristics. The active synthetic fragment of bovine PTH, bPTH-(1-34), at a concentration of 1 microM, significantly enhanced the magnitude of L-channel currents by 67.8% (n = 13, p less than 0.01). The steady-state activation curve of L-channel currents was shifted along the voltage axis toward more negative potentials by either bPTH-(1-34) or Bay K-8644. The suppression or amplification of PTH-induced enhancement of inward currents by nifedipine, 1 microM, or Bay K-8644, 5 microM, respectively, further indicated that the effect of PTH was specific for L-type calcium channels. However, bPTH-(1-34) failed to modulate the magnitude or kinetics of T-channel currents. This study directly demonstrates that PTH is a specific endogenous calcium-channel activator in neonatal rat ventricular cells.

Animals↗
PubMed1991

Parathyroid hormone selectively inhibits L-type calcium channels in single vascular smooth muscle cells of the rat.

1. The active synthetic N-terminal fragment of bovine parathyroid hormone, bPTH-(1-34) at a concentration of 1 microM, decreased the peak amplitude of the long-lasting (L-type) calcium channel current by 37% (n = 14, P less than 0.01) in rat tail artery smooth muscle cells. By contrast, this fragment of parathyroid hormone (PTH) (1 microM) had no effect on the transient (T-type) calcium channel current in the same cell preparation. 2. The inhibitory effect of bPTH-(1-34) on L-channel currents was reversible and could be antagonized by the L-channel agonist, Bay K 8644. In contrast, bPTH-(1-34) inhibited Bay K 8644-induced amplification of L-channel currents. 3. The inhibitory effect of bPTH-(1-34) on L-Channel currents was dose dependent with a threshold concentration of less than 10(-7), and voltage dependent with increased inhibition at more positive holding potentials. However, this effect of bPTH-(1-34) was not dependent on different pulse lengths or interpulse intervals. 4. The kinetics of deactivation of L-channel currents were not changed although the instantaneous amplitude of the L-channel tail current was reduced by bPTH-(1-34). 5. Application of bPTH-(1-34) antagonists (10(-6) M-bPTH-(3-34) and 10(-5) M-bPTH-(7-34] did not result in any significant change in the magnitude of L-channel currents (n = 15 and n = 7, respectively). 6. Pre-incubation of cells with bPTH-(3-34) for more than 15 min abolished the inhibitory effect of bPTH-(1-34) on L-channel currents. 7. The present study provides direct evidence to demonstrate the PTH, an endogenous circulating hormone, is a selective inhibitor of L-channel currents in vascular smooth muscle cells.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

The polyomavirus early region gene in transgenic mice causes vascular and bone tumors.

Transgenic mice carrying the entire polyomavirus (Py) early region consistently develop both vascular and bone tumors. This tumor spectrum represents a subset of the tumors found in mice infected with Py and an expansion of the vascular tumor spectrum seen in Py middle T antigen (MT) transgenic mice (V. L. Bautch, S. Toda, J. A. Hassell, and D. Hanahan, Cell 51:529-538, 1987). Transgenic mice of three independent lineages develop these pathologies, and mice of individual lineages also develop lymphangiomas and fibrosarcomas. All tumors are of mesenchymal origin, and all tumor tissues express the Py transgene. Some unaffected tissues, including the testes of mice of all lineages, also express the Py transgene. The number of transgene expression sites in mice of a given lineage correlates with the severity and latency of the tumor phenotype in these animals. Analysis of transgene transcripts indicates that RNAs for Py large T antigen (LT), MT, and small T antigen (ST) are present in both tumors and testes of transgenic mice. The ratio of LT RNA to MT and ST RNAs, however, is higher in testes than in tumors and other unaffected tissues, indicating that tissue-specific differences in the relative amounts of the alternatively spliced Py RNAs exist. The finding that some sites of Py transgene expression are susceptible to tumor formation while other expressing tissues such as testes are refractory to tumorigenesis suggests that mechanisms of viral pathogenesis are influenced by a tissue specificity in the effects of the Py early region.

Animals↗
PubMed1991

Does pentobarbital anesthesia depress left ventricular contractility in dogs?

Although pentobarbital sodium (NP) anesthesia has been shown to depress left ventricular (LV) contractility in dogs, measurements of LV contractility in previous studies have been made soon after a bolus of NP was given when serum concentrations would be extremely high. In this study, we compared indexes of LV contractility during awake and anesthetized conditions. During anesthesia, measurements were obtained 1 h after an intravenous bolus of NP was given when serum concentrations were approximately 25 mg/l and above that reported to abolish pain. In 13 dogs, subendocardial ultrasonic crystal transducers and a high-fidelity pressure transducer were implanted into the LV. Measurements were obtained with and without prior treatment with propranolol to produce beta-adrenergic blockade. LV contractility was assessed by ejection fraction and the end-systolic pressure-volume relationship. The effect of NP on ventricular myocardium was also examined in an in vitro canine right trabecular preparation to compare in vivo and in vitro effects. In the in vivo study, the results showed no decrease in LV contractility during anesthesia regardless of whether propranolol was administered. The in vitro preparation showed only a minimal decrease in isometric tension at the concentrations used in the in vivo study. We conclude that NP anesthesia does not depress LV contractility when concentrations are maintained at approximately 25 mg/l.

Analysis of Variance↗
PubMed1991

A modified electrode plate for low energy electric conversion of atrial fibrillation.

Fifty-six patients with atrial fibrillation associated with heart disease were treated with a modified electrode plate for low energy electric conversion. Fifty-four (96%) of these cases were successfully converted into sinus rhythm using the modified electrode plates, a new site and low energy discharge (an average of about 50 J). To construct the new-style electrode plates, a 2 cm arc segment was cut from each of two electrodes (10 cm in diameter each). As for the site of application, the cut-edge of the anterior chest electrode, which has a concave diameter of 150 cm, is placed close to the right of the sterum over the fourth to sixth intercostal spaces, and the cut-edge of the other electrode is placed to the left of the spinal column at the level of the seventh to ninth thoracic vertebrae. The safe-effective period for the appearance of the first post-discharge QRS complex was found to be 1.4-5.0 s.

Adult↗