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F Hwang

Publications and source records attributed to F Hwang.

At least 19 recordsLinked to original sources
PubMed1998

Automatic probe tuning and matching.

The problem of automatically tuning and matching a probe is considered, and attention is drawn to the main cause of difficulty: the interaction of tuning and matching mechanisms. The use of a doubly resonant, inductively coupled probe is therefore advocated, for to first order, tuning, and matching are then orthogonal for small perturbations. It is shown that when such a probe is equipped with negative feedback control of tuning and matching elements, driven by error signals derived from a bridge and the NMR spectrometer, stable and rapid automatic tuning and matching are achieved. The importance of approximately correct phasing of the error signals is emphasized, but the restriction of having to have specific cable lengths to achieve this task is removed. The effects of small errors of phasing are then considered and shown to be unimportant for the chosen probe, in contrast to the situation for other, nonorthogonal probe types. Suggestions for orthogonalization of two common capacitively coupled probe designs are made, and a practical instrument design is then given that, with the addition of external components, can also be used if the NMR receiver cannot be pressed into service.

Equipment Design↗
PubMed1998

Effects of La3+ on lipid fluidity and structural transitions in human erythrocyte membranes.

The effects of La3+ on the structure and function of human erythrocyte membranes were investigated by fluorescence polarization, spin-labeled electron spin resonance (ESR) and differential scanning calorimetry (DSC). The results showed that increasing concentrations of La3+ inhibited (Na(+) + K+)-ATPase and Mg(2+)-ATPase activities. La3+ lowered the lipid fluidity of erythrocyte membranes and induced structural transitions in erythrocyte membranes.

Ca(2+) Mg(2+)-ATPase↗
PubMed1998

Safety, pharmacokinetics, and antiretroviral activity of intravenous 9-[2-(R)-(Phosphonomethoxy)propyl]adenine, a novel anti-human immunodeficiency virus (HIV) therapy, in HIV-infected adults.

9-[2-(R)-(Phosphonomethoxy)propyl]adenine (PMPA) is a nucleotide analogue with potent antiretroviral activity in vitro and in simian models. A randomized, double-blind, placebo-controlled, dose-escalation clinical trial of intravenous PMPA monotherapy was conducted in 20 human immunodeficiency virus (HIV)-infected adults with CD4 cell counts of >/=200 cells/mm3 and plasma HIV RNA levels of >/=10,000 copies/ml. Two dose levels were evaluated (1 and 3 mg/kg of body weight/day). Ten subjects were enrolled at each dose level (eight randomized to receive PMPA and two randomized to receive placebo). On day 1, a single dose of PMPA or placebo was administered by intravenous infusion. Beginning on study day 8, PMPA or placebo was administered once daily for an additional 7 consecutive days. All subjects tolerated dosing without significant adverse events. Mean peak serum PMPA concentrations were 2.7 +/- 0.9 and 9.1 +/- 2.1 microgram/ml in the 1- and 3-mg/kg cohorts, respectively. Serum concentrations declined in a biexponential fashion, with a terminal half-life of 4 to 8 h. At 3 mg/kg/day, a single infusion of PMPA resulted in a 0.4 log10 median decline in plasma HIV RNA by study day 8. Following 7 consecutive days of study drug administration thereafter, the median changes in plasma HIV RNA from baseline were -1.1, -0.6, and 0.1 log10 in the 3-mg/kg/day, 1-mg/kg/day, and placebo dose groups, respectively. Following the final dose in the 3-mg/kg/day cohort, the reduction in HIV RNA was sustained for 7 days before returning toward baseline. Further studies evaluating an oral prodrug of PMPA are under way.

Adenine↗
PubMed1995

Caffeine-halothane accuracy in MH testing.

The accuracy and stability of caffeine and halothane concentrations in liquid Krebs medium were examined. Caffeine-Krebs Ringer's solution in incremental concentrations from 0.25 to 10 mM (N = 8 for each concentration) was serially assayed over a three-year period. Storage was at 4 degrees C. For serial testing of halothane during a five month period, halothane 1% or 3% in carbogen was bubbled through a Krebs solution, contained in muscle baths, either using a roller pump (to eliminate vaporizer back pressure) or using carbogen at a line pressure of 4-6 lbs/in2 (27-41 kPa). Halothane in Krebs was assayed by high pressure liquid chromatography. Caffeine concentrations did not vary for 20 weeks. From then, through 60 weeks, concentrations less than 2 mM steadily diminished; after that, through 156 weeks, only 4, 8, and 10 mM were stable. When compared to the halothane concentration in gas entering the muscle baths, halothane concentration in Krebs was predictable regardless of method delivery, as long as a gas analyzer indicated the proper concentration. We conclude that caffeine solutions are stable for 20 weeks when refrigerated, and for three years at concentrations 4 mM or greater.

Caffeine↗
PubMed1994

Interaction of the interdigitated DPPG or DPPG/DMPC bilayer with human erythrocyte band 3: differential scanning calorimetry and fluorescence studies.

Human erythrocyte band 3 reconstituted into phospholipid vesicles has been used for studying the interaction of interdigitated lipid bilayer with an integral membrane protein. The interdigitated gel phase in DPPG/band 3 or DPPG/DMPC/band 3 systems was induced with polymyxin B (PMB) or Tris+. The phase transitions of the vesicles were detected with high-sensitivity differential scanning calorimetry (DSC). The results indicated that band 3 does not cause significant alterations in the interdigitated phase of phospholipids, with only a little decrease of the phase transition enthalpies. Fluorescence measurements showed that the transition of phospholipid/band 3 systems from the non-interdigitated to interdigitated phase is accompanied by marked intrinsic fluorescence changes of band 3. The interdigitated phase of DPPG or DPPG/DMPC vesicles increases the intrinsic fluorescence intensity of band 3 and significantly decreases the accessibility of certain tryptophan residues on the protein to Cs+.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1994

Effect of lanthanide ions on the phase behavior of dipalmitoylphosphatidylcholine multilamellar liposomes.

The effect of lanthanide ions (Ln3+) and their coordination compounds of diethylenetriamine pentaacetic acid (DTPA) on the phase behavior of dipalmitoylphosphatidylcholine (DPPC) multi-lamellar liposomes has been studied by differential scanning calorimetry (DSC), Raman spectroscopy, and freeze-fracture electron microscopic techniques. The displacement of Ca2+ binding on DPPC liposomes by lanthanide ions was also studied. The results show that the binding degree of four kinds of chloride salts with DPPC liposomes is: YbCl3 > GdCl3 > LaCl3 > CaCl2. Lanthanide ions increase the phase transition temperature of DPPC liposomes and decrease the membrane fluidity. Freeze-fracture electron microscopic results show that La3+ enhances the order of DPPC membrane. The effect of coordination compounds of lanthanides with DTPA on the phase behavior of DPPC liposomes is smaller than that of their chlorides. La3+, Gd3+, and Yb3+, can displace Ca2+ binding on DPPC liposomes, but there coordination compounds of DTPA can hardly displace Ca2+. Raman spectroscopic results show that a very slight effect in lateral packing order of DPPC liposomes was observed at various concentrations of lanthanides.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1993

Anisodamine causes acyl chain interdigitation in phosphatidylglycerol.

The effect of anisodamine on the structure of the gel phase and the properties of the acyl chain disordering transition of dipalmitoylphosphatidylglycerol (DPPG) has been studied through high-sensitivity differential scanning calorimetry (DSC) and fluorescence polarization measurements of 16-(9-anthroyloxyl)-palmitic acid (16AP) and 3-(9-anthroyloxyl)-stearic acid (3AS), labeling, respectively, the ends and the third carbon of the acyl chains. The non-interdigitated DPPG multilamellar vesicles formed in HEPES buffer show clear fluidity gradient in their acyl chains, whereas the fluidity gradients are completely abolished in the presence of anisodamine. The DSC results showed that the phase transition temperature (Tm) of DPPG is decreased and the enthalpy (delta H) is increased by anisodamine, while the pre-transition vanishes. At 3 mM anisodamine, the delta H of DPPG reaches 9.6 kcal/mol. It can be concluded that DPPG forms an interdigitated gel phase in the presence of anisodamine. A molecular scheme for the interaction of anisodamine with DPPG is proposed.

Acylation↗
PubMed1993

Phase transitions of Acholeplasma laidlawii membranes. The involvement of Mg(2+)-ATPase in the C transition.

Highly sensitive differential scanning calorimetry has been employed to study the phase transitions of A. laidlawii membrane. The DSC curves obtained show five distinct transitions between 20 and 80 degrees C which contain a reversible lipid thermotropic transition at about 37 degrees C and four irreversible denaturation transitions of the membrane proteins occurred at about 44 degrees C, 52 degrees C, 62 degrees C, and 67 degrees C, respectively. Total enthalpy of the thermal denaturation of membrane proteins is 3.4 +/- 0.5 cal/g. Further study of A. laidlawii membrane preparations by means of thermal gel analysis and enzyme activity measurements at various temperatures provided information that the third peak (C transition) of the DSC curve involved primarily with Mg(2+)-ATPase on A. laidlawii membranes.

Acholeplasma laidlawii↗
PubMed1992

Definition of microsatellite size variants for Tnfa and Hsp70 in autoimmune and nonautoimmune mouse strains.

We have cloned and sequenced the upstream regulatory region of tumor necrosis factor alpha (Tnfa) gene in 12 different mouse strains and identified an allelic polymorphism in the upstream regulatory region of the mouse Tnfa gene. The TNF allele found in the NZW strain is distinct from those of all other H-2 haplotypes, supporting our previous suggestion that this allele may be associated with a regulatory or structural defect. In addition, simple tandem repeat sequences (microsatellites) within the promoter region of the Tnfa gene and the 3' untranslated region of one of the members of the HSP70 family (Hsp68c clone) were utilized as genetic markers. Ten TNF size variants and twelve HSP70 variants were identified in over forty mouse strains. Using these markers in a set of congenic mice, we mapped this member of the HSP70 family to the central portion of the H-2 complex, centromeric to the Tnfa gene. The NOD and NZW strains carry unique HSP70 alleles based on the variability in the length of this marker. These findings raise the possibility that this protein may play a role in the association of the major histocompatibility complex with these autoimmune diseases.

Animals↗
PubMed1992

Effect of hydroxyl radical on Na(+)-K(+)-ATPase activity of the brain microsomal membranes.

Sphingomyelin liposomes and brain microsomes were oxidized by exposure to hydrogen peroxide and ferrous ion. Lipid peroxidation were measured by the formation of thiobarbituric acid- reactive substances (TBAR). Hydroxyl radical was detected using the spin- trapping technique. Incubation of sphingomyelin liposomes with H2O2-Fe2+ resulted in an increase in the formation of TBAR. Na(+)-K(+)-ATPase activity was markedly inhibited and the SH group content decreased during incubation of microsomes in the presence of H2O2-Fe2+. Sodium ferulate effectively inhibited TBAR formation, protected Na(+)-K(+)-ATPase activity and prevented the oxidative modification of SH groups. Spin-trapping experiments showed that sodium ferulate effectively scavenged the hydroxyl radicals.

Animals↗
PubMed1991

Expression of protein kinase C isoenzymes in thymocyte subpopulations and their differential regulation.

The expression of the different protein kinase C (PKC) isozymes in mouse thymocytes was studied to determine if there is a correlation between isozyme expression and thymocyte phenotype. Expression of PKC isozymes in thymocyte subsets (distinguished by the CD4 or CD8 Ag) was determined by message amplification phenotyping. The expression of mRNA for PKC-alpha, -beta, -epsilon, and -zeta, but not -gamma or -delta isozymes, was detected in all of the unstimulated thymocyte subpopulations analyzed. Thus no differences in the pattern of PKC isozyme expression were found that could be correlated with thymocyte phenotype. However, it was noted that the levels of PKC mRNA expression were affected by different stimuli in unfractionated thymocytes. Whereas mRNA levels of PKC-alpha and -beta were down-regulated by PMA and ionomycin treatment, no significant changes were seen in the levels of PKC-epsilon mRNA with these agents. PKC-epsilon mRNA decreased in thymocytes exposed to Con A similar to what has been reported for PKC-epsilon protein. PKC-zeta mRNA was also down-regulated by PMA or ionomycin, and the combination of both compounds caused a more rapid and drastic effect. Finally, PKC-delta mRNA expression was induced transiently in thymocytes only after exposure to PMA or Con A, and this induction was inhibited by ionomycin treatment. These results indicate that message levels of specific isoforms of PKC are uniquely regulated and suggest an additional level of control of PKC activity in activated lymphocytes.

Animals↗
PubMed1991

Tumor necrosis factor alpha in murine systemic lupus erythematosus disease models: implications for genetic predisposition and immune regulation.

Recombinant tumor necrosis factor alpha (TNF-alpha) administration significantly delayed the development of lupuslike nephritis in the New Zealand black x New Zealand white (NZB x NZW)F1 and to a lesser extent in the MRL-lpr/lpr model systems. TNF-alpha treatment was effective when treatment was initiated at 2, 3, or 4 months of age but was ineffective if initiated as late as 6.5 months of age. Treatment of (NZB x NZW)F1 mice for 3 months was more effective than treatment continued for 6 months. Anti-TNF-alpha antibodies did not develop in these mice. Flow microfluorometry analysis showed no major effects on B, T, or monocyte cell population in cells from the peritoneum, spleen, lymph node, and thymus. A decrease in class II Ia expression on macrophages in the peritoneum of TNF-alpha-treated mice was noticed. A correlation between the level of TNF-alpha inducibility in vitro and the effect of TNF-alpha administration in vivo could be shown. Although a limited polymorphism could be shown by restriction fragment length polymorphism, using an amplified (AC)n microsatellite located in the 5' regulatory region of TNF-alpha, a much more extensive interallelic polymorphism was found. The AC microsatellite allele found in NZW mice was unique and different from other lupus strains and nonautoimmune strains. These results have possible implications to the pathogenesis of systemic lupus erythematosus.

Animals↗
PubMed1991

Immunological properties of antibodies against Mg(2+)-ATPase from Acholeplasma laidlawii membranes.

In the present study, antibodies were raised against the Mg(2+)-ATPase and the immunological relationships between the enzyme and other ATPase from a variety of biological membranes were determined. The anti Mg(2+)-ATPase antiserum inhibited 85% of the enzyme activity from A. laidlawii membranes. We demonstrate a specific selectivity of Mg(2+)-ATPase antiserum for antigenic determinants of the A. laidlawii membranes. Immunoblot studies of A. laidlawii membrane peptides indicated labeling of five bands, 66KD, 49KD, 34KD, 26KD and 13KD, corresponding to five subunits of the ATPase in A. laidlawii membranes.

Acholeplasma laidlawii↗
PubMed1990

Supersensitivity to electrical stimulation for assessing physical dependence on opioids in isolated tissues.

The use of the guinea pig ileum (GPI) and mouse vas deferens (MVD) to quantify opiate tolerance and physical dependence in the same preparation was examined. In the GPI, tolerance to and physical dependence on various opiates were induced by direct incubation with an agonist and tolerance and abstinence were assessed after its rapid removal by extensive washing. Dependence, as evidenced by an increase in twitch height and after removal of the agonist as compared to that before incubation, provided an index of the degree of physical dependence. The extent of the supersensitive response after agonist removal was noted to be related directly to the agonist concentration and the degree of tolerance development. Furthermore, the supersensitive response was found to be stereospecific, naloxone reversible and preferentially mu receptor-mediated. Likewise, tolerance to opiates could be demonstrated in the MVD by direct incubation with an agonist. Unlike the GPI, rapid removal of the agonist by washing did not produce a supersensitive response to electrical stimulation. However, a supersensitive response was demonstrable in the presence of naloxone. Thus, after a tolerant/dependent state was induced by incubation of the vas with a predetermined dose of [D-Ala2, D-Leu5]enkephalin that completely abolished the twitch response, the subsequent addition of naloxone resulted in a supersensitive response to electrical stimulation that was concentration-dependent. The maximum twitch response in the presence of naloxone, compared to that obtained before incubation with the agonist, provided an index of the extent of dependence.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Anisodamine induces the hexagonal phase in phospholipid liposomes.

The effects of anisodamine on the polymorphic phase behaviour of cardiolipin and dioleoylphosphatidylcholine liposomes have been investigated by freeze-fracture electron microscopy. Anisodamine induces the formation of lipidic particles in cardiolipin liposomes at pH 7.0 and hexagonal HII tubes at pH 8.8. When the molar ratio of anisodamine and dioleoylphosphatidylcholine is 4 to 1, lipidic particles can be observed in the fracture faces.

Cardiolipins↗
PubMed1986

Studies on the phospholipid composition of pathogenic cell membranes of Mycoplasma hyopneumoniae.

The membrane phospholipid and fatty acid compositions of Mycoplasma hyopneumoniae, a pathogen of porcine enzootic pneumoniae isolated in China, was studied by thin-layer chromatography and gas chromatography. The results showed that membrane phospholipids consisted predominantly of diphosphatidylglycerol. The percentage of C16 - C18 fatty acids comprised 79% of the total fatty acids, of which oleic acid as well as palmitic acid are the major fatty acids. Some differences were shown in fatty acid composition as compared with membranes of other species of Mycoplasma.

Cell Membrane↗
PubMed1985

Inhibition of epidermal growth factor-induced phosphorylation by trifluoperazine.

We studied the effects of a series of drugs on A431, a cell line with well-characterized growth factor requirements and epidermal growth factor (EGF) receptors. The major [32PO4]-labeled protein immunoprecipitated with anti-phosphotyrosine antibodies from EGF-stimulated A431 cells was the EGF receptor. Both the quantity of [32PO4]-labeled EGF receptor immunoprecipitated and the phosphotyrosine content of total [32PO4]-labeled proteins were reduced by the addition during EGF stimulation of trifluoperazine (TFP). TFP had little effect on the binding, internalization, and processing of [125I]-EGF. In addition to the effects on phosphorylation, TFP inhibited cell growth both in the presence and absence of EGF. Morphologically, TFP blocked EGF-induced ruffling. TFP did not alter the EGF-stimulated phosphatidylinositol turnover. In an in vitro experiment using A431 cell membranes, TFP did not inhibit phosphorylation of the EGF receptor.

Animals↗