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Biomedical subjects

T M Chen

Publications and source records attributed to T M Chen.

At least 127 records · Page 7Linked to original sources
PubMed1986

Studies of kissing bug-sensitive patients: evidence for the lack of cross-reactivity between Triatoma protracta and Triatoma rubida salivary gland extracts.

In the southern and western sections of the United States, bites from the reduviid bug, commonly known as the kissing bug, genus Triatoma, may induce serious life-threatening allergic reactions. This study was undertaken to identify the allergens responsible for patient sensitization and to determine the extent of cross-reactivity of these allergens. The Triatoma spp. most commonly encountered in California and Arizona, T. protracta and T. rubida, were obtained, maintained in the laboratory, and dissected to prepare extracts for testing. Extracts were prepared from T. protracta and T. rubida for study by RAST, lymphocyte transformation, leukocyte histamine release, and RAST inhibition. Sera and cells were collected from patients who had generalized reactions to Triatoma bites. Our results indicate that T. protracta and T. rubida antigens to which patients are sensitized are present in extracts that contain saliva and that human responses are specific for T. protracta or T. rubida, i.e., allergic cross-reactivity could not be demonstrated.

Adolescent↗
PubMed1985

Construction of a conjugative plasmid with potential use in vaccines against heat-labile enterotoxin.

A conjugative plasmid with potential usefulness for vaccine strains was constructed. In the first step, a 5.9-kilobase DNA segment containing the two loci for the A and B subunits of heat-labile enterotoxin with a mutation in the gene for the A subunit was joined to the cloning vehicle pGA22, generating the nonconjugative plasmid pPMC4 with genes for resistance to tetracycline and chloramphenicol. In the second step, a segment of pPMC4 containing the genes for the A and B subunits, the gene for chloramphenicol resistance, and the replication genes of pGA22 was ligated to the genes for conjugal transfer of the F plasmid, generating the 54.9-kb plasmid pPMC5. Eleven porcine Escherichia coli isolates were tested as recipients for pPMC4 and pPMC5. For pPMC4, transformation and mobilization with a conjugative R plasmid were used to effect plasmid transfer. Only 1 of the 11 strains acted as a recipient in transformation. Mobilization with the R plasmid occurred with two strains, but the plasmids were altered during transfer. In contrast, pPMC5 was transferred with high frequency and unaltered to 9 of the 11 E. coli strains. Transconjugants from these nine matings produced high titers of the B subunit and no active heat-labile enterotoxin. Plasmid pPMC5 was stable in three porcine E. coli strains tested; plasmid pPMC4 was somewhat less stable in these strains. The method we describe for the construction of conjugative chimeric plasmids offers an opportunity for introducing genes with potential for immunization into bacterial strains that are suitable for colonizing the appropriate host sites.

Animals↗
PubMed1984

Effects of Chemical Treatments upon Photosynthetic Parameters in Soybean Seedlings.

The effects of various chemical treatments upon photosynthesis, soluble leaf protein, CO(2) compensation point, and leaf light transmission in soybean, Glycine max (L.) Merr., seedlings were examined following varying response periods after application at 14 to 17 days postemergence. The compounds N(6)-benzyladenine (BA), 2-(4-chlorophenoxy)-2-methylpropanoic acid (CPMP), (4-chlorophenoxy)acetic acid (CPA), rhodanine-N-acetic acid (RAA), and 2,3,5-triiodobenzoic acid (TIBA) significantly increased soluble protein and decreased senescence, measured by leaf light transmission, at CO(2) concentrations below the compensation point in a survival chamber. All compounds except BA significantly decreased transmission values under ambient atmospheric conditions. In statistically significant experiments, applications of 3.49 millimolar CPMP increased net photosynthesis on a leaf area basis by an average of 14.4% at all trifoliolate positions with increases generally requiring response periods of 12 days or longer. RAA at 1.31 and 2.61 millimolar increased net photosynthesis by 19 to 36% following 13-day response periods. CPMP and other compounds tested had no effect upon the CO(2) compensation point after 4- to 8-day response periods. The effects of CPMP and RAA upon net photosynthesis and soluble protein appeared to involve a combined stimulation of protein synthesis and an antisenescent effect. There were no indications that any of the photosynthetic changes observed resulted from direct differential effects upon ribulose bisphosphate carboxylase-oxygenase. The assays for soluble protein and light transmission responded more consistently to the chemicals than did photosynthesis.

Journal Article↗
PubMed1984

Detection of chemicals inhibiting photorespiratory senescence in a large scale survival chamber.

A large scale survival chamber was developed as a screen for detecting chemical treatments that extend the survival time of illuminated soybean seedlings at CO(2) concentrations below the compensation point. In theory, extended survival should indicate potential for improved crop performance via decreased photorespiration and increased photosynthetic efficiency. An automated control system regulated CO(2) concentrations, temperature and plant watering during a continuous CO(2)-removal photoperiod of 72 hours. An endogenously controlled circadian rhythm of net photosynthesis occurred throughout the continuous light treatment.Spray applications of 3.49 millimolar 2-(4-chlorophenoxy)-2-methylpropanoic acid (CPMP) significantly decreased leaf chlorophyll loss, compared with the control, after 72 hours of subcompensation-point stress. Treatment with CPMP also consistently increased leaf chlorophyll per unit area under nonstress greenhouse conditions. These effects may be due to increases in specific leaf weight produced by CPMP although the compound did not consistently act as a height retardant. The compound, 3-butyl-2-hydroxy-4H-pyrido[1,2-a]pyrimidin-4-one (BHPP), inhibited senescence under low CO(2) conditions but did not decrease leaf light transmission at ambient CO(2) levels. The cytokinin N(6)-benzyladenine (BA) retarded low CO(2) stress senescence although greening effects were not observed. Neither 2-hydroxy-3-butynoic acid (HBA) nor its butyl ester, inhibitors of glycolate oxidase, influenced low CO(2) survival. Cyclohexanecarboxylic acid (CHCA) and sodium naphthenate had no effect upon subcompensation-point senescence.Antisenescence effects of CPMP, BHPP, and BA do not appear to be directly attributable to effects upon the competing carbon paths of photosynthesis and photorespiration. Protection against low CO(2) stress and increased chlorophyll synthesis under nonstress conditions may represent separate effects upon plastids by some of the compounds. This screen will identify compounds which inhibit photorespiratory senescence without decreasing the CO(2) compensation point.

Journal Article↗
PubMed1982

Solvent effects on bonding organo-silane to silica surfaces.

Interfacial bonding and stability of gamma-methacryloxypropyltrimethoxysilane with silica surfaces have been studied by means of infrared spectroscopy. The addition of n-propylamine enhances silanization of gamma-methacryloxypropyltrimethoxysilane to silica surfaces in normal aliphatic hydrocarbons, and cyclohexane yields a more water-resistant silica-silane bond, and improves the diametral tensile strength of the composite.

Acrylates↗
PubMed1981

High-pressure liquid chromatographic assay of theophylline, ephedrine hydrochloride, and phenobarbital tablets.

An innovation high-pressure liquid chromatographic method is described in which theophylline, ephedrine hydrochloride (measured as benzaldehyde), and phenobarbital are determined simultaneously with butabarbital as the internal standard. Chromatographic conditions were selected to afford a pH sufficient for rapid oxidation of ephedrine and relatively high UV absorbance for the barbiturates and a detection wavelength near the maximum for benzaldehyde and the barbiturates and the minimum for theophylline. Chromatograms show peaks from iodate, theophylline, phenobarbital, butabarbital, and benzaldehyde, in order of increasing retention time, all within the dynamic range of a conventional recorder. Procedures are provided for the assay of conventional and sustained-action tablet formulations.

Chromatography, High Pressure Liquid↗
PubMed1980

Thalifaurine and dehydrodiscretine, new quaternary protoberberines from Thalictrum fauriei.

Two new quaternary protoberberines, thalifaurine and dehydrodiscretine, were isolated from the ethanolic extract of Thalictrum fauriei Hayata. Based on spectral analysis and correlation with compounds of known structure, thalifaurine was shown to be 3-hydroxy-2-methoxy-10,11-methylenedioxyberbinium chloride and dehydrodiscretine was established as 3-hydroxy-2,20,11-trimethoxyberbinium chloride. The structural assignment was confirmed by synthesis of both compounds. Magnoflorine also was isolated and identified.

Alkaloids↗
PubMed1978

Measurement of frequency of ciliary beats of human respiratory epithelium.

A method for accurate measurement of beats on ciliated respiratory epithelial cells in vitro is described. The technique allows the frequency of ciliary beats to be recorded directly on minute specimens of human respiratory epithelium obtained by bronchoscopic brushing. A "hanging-drop" preparation of the scraped material is placed on a thin, flat welled slide and is viewed with a phase-contrast microscope at a magnification of x450. Light transmitted through the specimen is deflected in varying intensities due to the beating action of the cilia and is detected by a photomultiplier cell, amplified and transduced as peaks on an oscilloscope. Due to the relatively high magnification, a small group of cilia may be focused upon and their activity measured. Specimens from two groups totaling 53 patients were measured; in the first group the frequency of ciliary beats was measured at 23 degrees C and ranged from 9.1 to 12.9 beats per second with a mean and standard deviation of 11.0 +/- 1.3 beats per second. The second group was measured at 37 degrees C, and values ranged from 10.3 to 16.8 beats per second, with a mean and standard deviation of 13.8 +/- 1.8 beats per second. These values are interpreted to reflect the autonomous frequency of ciliary beats of the isolated respiratory cells. This simple method may be applied to screen for abnormalities of ciliary beating in patients with altered respiratory mucous clearance, as well as to examine the specific effects in vitro of chemicals, drugs, or pollutants on human ciliary activity.

Adult↗
PubMed1978

Mucus viscoelasticity and mucociliary transport rate.

The aim of this research was to define in quantitative terms the relationship between the viscoelastic properties of mucus and the velocity at which it can be transported by a ciliated mucosa. To this effect, tests were performed on frog palates with normal beating cilia which were washed free of endogenous mucus. Experimental sputum samples encompassing a wide range of viscoelastic properties were applied to the palates, and their transport velocity was measured under a dissecting microscope. The results indicated that the fastest transport, per palate, was achieved by sputa whose Newtonian viscosity and linear elastic modulus fell within the range of 1,000 to 3,000 poises and 10 to 25 dynes/cm2, respectively. The transport velocity decreased when the sputum viscoelasticity was above or below this optimal range. The latter condition is of particular importance since it indicates that marked fluidification may hinder rather than promote mucus clearance.

Animals↗