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Biomedical subjects

T Chun

Publications and source records attributed to T Chun.

27 records · Page 2Linked to original sources
PubMed1998

Oxidative stress suppresses the endothelial secretion of endothelin.

To address endothelial function on vascular walls exposed to oxidative stress, we investigated the effect of oxidative stress on the secretion of endothelin-1 (ET-1) from cultured bovine carotid artery endothelial cells (BAECs). Concentrations of ET-1 in the media were measured by a specific radioimmunoassay and ET-1 mRNA expression was estimated by Northern blot analysis. Treatment of BAECs with 0.5-2.0 mM H2O2 for 3 h suppressed both ET-1 secretion and ET-1 mRNA expression in a dose-dependent manner compared to control. Attenuation of ET-1 mRNA expression by H2O2 was revealed to take place at the transcriptional level. The addition of NG-nitro-L-arginine-methyl ester (L-NAME) 10 microns, a specific nitric oxide synthase inhibitor, had no effect on H2O2-induced suppression of ET-1 mRNA expression. Suppression of ET secretion under oxidative stress observed in the present study is proposed to be a compensatory mechanism of endothelial cells to inhibit vasoconstriction and proliferation during oxidative stress.

Animals↗
PubMed1998

Interferon-alpha and interferon-gamma differentially affect pancreatic beta-cell phenotype and function.

To better clarify individual roles of interferon (IFN)-alpha and IFN-gamma in beta-cell pathology during the onset of type 1 diabetes mellitus, we compared the effects of these cytokines on insulin production and major histocompatibility complex (MHC) gene expression in pancreatic beta-cell lines. IFN-gamma but not IFN-alpha decreased secreted and intracellular insulin concentrations in betaTC6-F7 and betaTC3 cells. Likewise, IFN-gamma but not IFN-alpha treatment of beta-cells upregulated mRNA expression of MHC class IA antigen-processing genes and surface expression of class IA molecules. Alternatively, class IA MHC expression was upregulated by IFN-gamma and IFN-alpha in the P388D1 macrophage cell line. The observation of constitutive Ifn-alpha6 mRNA expression by a differentiated beta-cell line substantiates previous indications that local expression of IFN-alpha in islets may trigger insulitis. Evidence that IFN-gamma, a product of infiltrating leukocytes, directly decreases beta-cell glucose sensitivity and increases MHC class IA cell surface expression supports the postulate that IFN-gamma magnifies the insulitic process.

Adenoma↗
PubMed1997

A novel method to determine the diffusional water permeability of oocyte plasma membranes.

Measurements of the cell membrane diffusional water permeability (Pd) are important to characterize water passage across water channels and across the lipid bilayer component of the membrane. Existing methods for those measurements are involved; however, we report here a simple procedure to estimate Pd in Xenopus laevis oocytes and similar large cells. Due to the different densities of H2O and D2O (heavy water), an oocyte transferred from normal medium to a D2O-based medium floats initially, but subsequently sinks when a certain amount of the water originally in them is replaced by the D2O that diffuses in. We describe how the 'flotation time' (time that oocytes float in a heavy water solution before they start sinking) yields the Pd of the plasma membrane. Determination of Pd by this procedure and by the rate of tritiated water (T2O) efflux give for Pd results which are very close: 2.2 +/- 0.2 (n = 8) and 2.0 +/- 0.1 (n = 6) microns/s, respectively (T = 10 degrees C). Furthermore, our method detects the increase in Pd elicited in oocytes by either expression of water channel proteins, or by treating them with the pore-forming antibiotic amphotericin B. This method appears useful to gauge the expression and function of pore-forming, water-permeable membrane proteins.

Amphotericin B↗
PubMed1990

Epithelial myoepithelial carcinoma of the parotid gland.

EMEC is a clear-cell tumor of salivary gland origin. Since it was first recognized as a distinct salivary gland malignancy in 1956, sporadic cases have been reported. A case of an EMEC in a parotid gland of a 77-year-old man is described. The clinical and histopathologic features of this unusual neoplasm, as well as a description of the immunohistochemistry and current management of this uncommon entity are presented.

Adenocarcinoma↗
PubMed1978

Some observations in a case of acoustic neuroma.

The subject was a 47-year-old male with a moderate asymmetrical sensorineural hearing loss that initially presented cochlear signs except for positive stapedius reflex results. Over the course of only five weeks, he developed the audiological constellation of retrocochlear involvement. The retrocochlear results were confirmed by the removal of an acoustic tumour. The results highlight the importance of audiological monitoring and reflex measures in the identification of acoustic neuromas. Several observations provide insight into the apparent relationship between loudness and the stapedius reflex. The findings are discussed with reference to a proposed extension of Borg's recent theory that elevated reflex thresholds and reflex decay reflect differing degrees of the eighth nerve destruction.

Auditory Threshold↗
PubMed1966

Chromosomal studies in children with mumps, chickenpox, measles and measles vaccination.

A study to assess chromosomal damage in persons with acute viral diseases was undertaken in view of conflicting reports in the literature concerning such damage. Forty children with measles, mumps, and chickenpox, or who had received measles vaccine, were investigated and compared with a control group of 12 children. No greater incidence of chromosomal abnormalities was found in the study group than in the control group.

Adolescent↗
PubMedDate not supplied

Diffusion changes in the aging human brain.

BACKGROUND AND PURPOSE: Quantifying changes in the human brain that occur as part of normal aging may help in the diagnosis of diseases that affect the elderly and that cause structural changes in the brain. We sought to assess diffusion changes that are inherently related to brain structure during aging. METHODS: MR scans were obtained from 11 healthy volunteers and 27 patients (ages 26 to 86 years [53.4 +/- 17.0 years]). Images acquired from the patients either showed no abnormalities, contained minimal periventricular white matter changes, or revealed focal lesions. Maps of the average diffusion constant (D(av)) were calculated for each subject. Changes in D(av) were determined with distribution analysis (histogram) for the entire brain and compared with region-of-interest measurements from the periventricular white matter and thalamus. RESULTS: Mean D(av) of the entire brain (0.74 +/- 0.02 x 10(-5) cm2/s) showed weaker age dependency compared with the periventricular white matter D(av)(0.76 +/- 0.04 x 10(-5) cm2/s). The D(av) of the thalamus D(av) (0.75 +/- 0.03 x 10(-5) cm2/s) had no age dependency. The age-dependent changes of entire brain D(av) may be significant for subjects older than 60 years compared with younger subjects. CONCLUSION: In this study, we observed minimal changes in the D(av) of the entire brain with aging. The mean D(av) of the human brain is nearly constant throughout most of adulthood.

Adult↗