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Biomedical subjects

K Wong

Publications and source records attributed to K Wong.

At least 181 records · Page 10Linked to original sources
PubMed1988

Translocation of protein kinase C in porcine thyroid cells following exposure to thyrotropin.

We have previously shown that protein kinase C activators modulate differentiated thyroid function in vitro; however, how protein kinase C may be activated physiologically is unknown. The present studies were undertaken in order to determine whether TSH could activate protein kinase C in vitro. Following exposure of porcine thyroid cells to TSH, translocation of protein kinase C from the cytosol to its membrane-bound form was observed. Maximal translocation occurred at the lowest TSH concentration able to trigger this response (10 mU/ml) but persisted at higher concentrations (20-100 mU/ml). Time-course studies revealed that translocation of protein kinase C was seen only after 40 min. TSH could also produce a similar translocation in human neutrophils (known to have TSH receptors). In thyroid cells pre-treated with TSH, modulation of phorbol-mediated protein kinase C translocation was noted. These results indicate that TSH causes the translocation of protein kinase C in porcine thyroid cells (and possibly other TSH receptor-containing cells) and therefore may regulate the action of protein kinase C on differentiated thyroid function.

Animals↗
PubMed1988

Dopamine accumulation in large unilamellar vesicle systems induced by transmembrane ion gradients.

Transmembrane movement of dopamine in response to K+ or H+ ion gradients has been investigated. It is shown that dopamine can accumulate rapidly into large unilamellar vesicles (LUVs) composed of egg phosphatidylcholine exhibiting either a K+ diffusion potential (delta psi; negative inside) or a pH gradient (inside acidic). This can result in entrapped dopamine concentrations of 30-40 mM and inside-outside concentration gradients of nearly 300-fold. The transmembrane dopamine gradients formed in LUV systems exhibiting delta pH (inside acidic) indicate that the transport process can be dictated by movement of the neutral form of dopamine which redistributes according to a simple Henderson-Hasselbach equilibrium. The mechanism of dopamine transport in response to a valinomycin-induced K+ potential is more complex. Although generation of a K+ diffusion potential results in acidification of the vesicle interior, the magnitude of the induced delta pH (approx. 1 pH unit) is insufficient to account for the dopamine concentration gradient achieved (greater than 200-fold). Further, data presented here suggest that higher uptake levels of dopamine can be achieved when certain anions (ATP and citrate) are entrapped within the LUV system. These anions may complex with the protonated form of dopamine creating a non-equilibrium trapping phenomena resulting in interior concentrations of dopamine in excess of that predicted by a simple Henderson-Hasselbach equilibrium.

Dopamine↗
PubMed1988

Primary intrasellar germinoma presenting with cavernous sinus syndrome.

A 28-year-old woman, 1 month post partum, who presented with headache and gradual onset of total ophthalmoplegia of the left eye, was found at transsphenoidal exploration to have a primary intrasellar germinoma. Craniospinal irradiation resulted in complete resolution of the intracranial tumor. Extensive mediastinal metastasis at 8 months after the operation resulted in a fatal outcome.

Adult↗
PubMed1988

Epstein-Barr virus genome in thymoma and thymic lymphoid hyperplasia.

In a study of 23 consecutive thymectomies from patients with myasthenia gravis (MG), 10 (43.5%) were thymomas, 8 (34.8%) were thymic lymphoid hyperplasia (TLH), and 5 (21.7%) were normal/involuted thymuses. The incidence of thymoma in MG appears to be considerably higher in Hong Kong than in similar series from Western countries. Six patients from this group were examined for the presence of Epstein-Barr virus (EBV) genome by Southern blot, as were a thymoma from a patient without MG, a patient with TLH in the absence of MG, and 3 normal control thymuses. All 3 thymomas (2 of 2 with MG, 1 of 1 without MG), 2 of 4 TLH with MG, and 1 of 1 TLH without MG were positive for EBV genome. Thymoma should be included, along with nasopharyngeal carcinoma and malignant lymphoepithelial lesions of the salivary gland, as EBV-related epithelial tumors, all of which are prevalent in this region.

Adult↗
PubMed1988

Comparison of ciprofloxacin assays.

Two high pressure liquid chromatography methods developed independently and two different microbiological methods assayed samples containing ciprofloxacin derived from four volunteers: 46 sera, 19 saliva and 27 urine specimens. Each subject had received 500 mg of ciprofloxacin by mouth, with the samples collected in the ensuing six hours. Fifteen mock unknowns, prepared by adding known amounts of ciprofloxacin to normal human serum, were also assayed by the four procedures. The limits of sensitivity of the HPLC assays were less than 0.01 microgram/ml; the sensitivity limits of the bioassay were 0.02 microgram/ml (disc method) and 0.06 microgram/ml (well method). The inter-assay data was analyzed by linear regression. Ciprofloxacin concentrations in serum samples correlated well (R = 0.90) with all methods. Values obtained with urine samples also correlated well (R greater than or equal to 0.80). We conclude that either microbiological assay or quantitation by HPLC is satisfactory for quantitation of ciprofloxacin.

Chromatography, High Pressure Liquid↗
PubMed1988

Role of the Ito cell in liver parenchymal fibrosis in rats fed alcohol and a high fat-low protein diet.

Eight pairs of young adult rats were pair-fed a high fat-low protein diet and ethanol or isocaloric glucose by permanent intragastric cannula for up to 6 months. Biopsies of the liver were taken monthly and the fibrosis was quantitated morphometrically using the sirius red polarization method of collagen visualization by light microscopy. Morphometric analysis of the sinusoids and scars were performed on electron micrographs made from the liver biopsies. An increase in the collagen in both the central and portal areas was found when the livers of the alcohol-fed rats were compared with controls. The predominant cell in the scars was the Ito cell. An increase in the percentage of the total Ito cell square area made up of rough endoplasmic reticulum (RER) was noted when the sinusoids of the liver of the ethanol-fed rats were compared with controls. No difference in the RER was found when the sinusoidal Ito cells were compared with the Ito cells located within the scars of the ethanol-fed rats. It was concluded that Ito cell "activation" by chronic ethanol feeding in the sinusoids of rats accurately predicts "activation" of the Ito cells within scars. The Ito cells are diffusely activated even though the scarring is localized. This implies that local factors as well as Ito cell activation are necessary for scar formation. In the case of alcoholic liver disease, scar formation may be initiated by centrilobular necrosis.

Animals↗
PubMed1987

Specific binding of leukotriene B4 to guinea pig lung membranes.

We have demonstrated binding sites for LTB4 in guinea pig lung membranes. Binding of [3H]-LTB4 was of high affinity (Kd = 0.76 nM), saturable and linear with protein concentration (0.2-1.2 mg/ml). Scatchard and Hill's plot analysis indicated a single class of binding site with a Hill's coefficient of 0.99 +/- 0.08 (n = 4). [3H]-LTB4 was unmetabolized during incubation with membrane preparations, as indicated by high performance liquid chromatography. Divalent cations such as Mg2+ and Ca2+ enhanced binding capacity without changing the Kd. Na+ ions decreased binding in a concentration-dependent manner. Guanine nucleotides, GTP, GTP gamma S and Gpp(NH)p also decreased the number of binding sites. Finally, competition experiments demonstrated the following order of potency for displacement of [3H]-LTB4 from its receptor site: LTB4 greater than 20-OH-LTB4 much greater than 20-COOH-LTB4 = 6-trans-12-epi-LTB4 greater than LTC4 = LTD4 = 5-HETE. These data indicate that a specific LTB4 receptor, in addition to the previously documented LTC4 and LTD4 receptors, exists in guinea pig lung.

Animals↗
PubMed1987

Quantitative and ultrastructural studies of excimer laser ablation of the cornea at 193 and 248 nanometers.

Excimer laser radiation at 193 nm and 248 nm was used to create linear etch perforations of enucleated calf corneas. The etch depth per pulse was determined for various exposures, and specimens were examined by light and transmission electron microscopy. Compared to 248 nm, excimer laser ablation at 193 nm was found to have a lower threshold for onset of ablation, less increase in etch depth per pulse at increasing fluences, and less structural alteration in adjacent cornea. For 193 nm, structural alterations were minimal, confined to an area less than 0.3 micron wide, and did not increase with increasing fluence. These studies suggest that clinical strategies for excimer laser refractive surgery will employ the 193-nm wavelength, with fluence chosen depending on surgical strategy. Ablation exposures above 600 mJ/cm2 at 193 nm may give the most repeatable etch depth.

Animals↗
PubMed1987

Gold compounds alter distribution of protein kinase C activity in human neutrophils.

Slow translocation of protein kinase C was observed by both auranofin and gold sodium thiomalate pretreatment of neutrophils. Both gold compounds failed to influence the activity of this enzyme directly when cell-free studies were performed. In intact neutrophils incubated with 5.1-20.3 microM auranofin, protein kinase C activity decreased in the cytosol in a time- and dose-dependent manner. Concomitantly, the levels of the membrane-associated protein kinase C were significantly elevated, although the amount of activity recovered could not account for that lost from the cytosol. Gold sodium thiomalate (5.0 microM-0.505 mM) demonstrated similar effects but with lesser potency than auranofin. In confirmation of previous results, phorbol myristate acetate (PMA), a cellular stimulus, also induced the translocation of protein kinase C. Key differences were that the reaction was rapid (occurring within minutes after PMA addition) and that relative recovery of kinase activity from the particulate fraction was fourfold greater. The relationship between gold compound-mediated kinase C redistribution and inhibition of neutrophil responses remains to be elucidated.

Cell Membrane↗
PubMed1987

Dual regulation of neutrophil adenylate cyclase by fluoride and its relationship to cellular activation.

1 Fluoride stimulated (1-10 mM) and inhibited (10-100 mM) adenylate cyclase of neutrophil membranes in a GTP-independent manner. The latter fluoride concentration range corresponded to that shown previously to induce cellular responses. 2 Dual regulation of cyclase activity was also exhibited by a nonhydrolysable GTP analogue, guanosine 5'[gamma-thio]triphosphate (GTP gamma S). Inhibition was observed at 0.1-10 nM GTP gamma S while stimulation occurred at greater than 10 nM GTP gamma S. 3 Relatively high levels (greater than microM) of formylmethionyl-leucyl-phenylalanine inhibited adenylate cyclase in the presence of GTP (10 microM). 4 Pertussis toxin pretreatment abolished adenylate cyclase inhibition mediated by GTP gamma S and formylmethionyl-leucyl-phenylalanine but did not influence fluoride-induced inhibition.

Adenylate Cyclase Toxin↗
PubMed1987

Suppression of superoxide generation by normal polymorphonuclear leukocytes preincubated in plasma from patients with Felty's syndrome.

Polymorphonuclear leukocytes (PMN) isolated from patients with Felty's syndrome (FS) generate fewer superoxide anions (O-2) upon stimulation with fmet-leu-phe than PMN from normal controls or patients with rheumatoid arthritis (RA). In this study, plasma samples were obtained from 12 patients with RA and 12 patients with FS. Incubation of normal PMN in plasma from Felty patients resulted in a significant reduction in both the rate and total quantity of O-2 generation when activated with fmet-leu-phe. This was not observed with plasma from RA patients. The capacity of a plasma sample to suppress O-2 generation correlated with plasma IgG-PMN-binding activity (IgG-PBA) and, to a lesser extent, with the content of circulating immune complexes (CIC). These data suggest that IgG-PBA and possibly CIC have a pathogenetic role in both qualitative and quantitative defects in PMN in Felty patients.

Aged↗
PubMed1986

GTP regulation of platelet-activating factor binding to human neutrophil membranes.

Radiolabeled ligand binding studies showed that specific receptors for platelet-activating factor are present in human neutrophil membranes. GTP at 10(-7) to 10(-3) M decreased the specific binding of platelet-activating factor to neutrophil membranes in a dose-dependent manner. Inhibition of platelet-activating factor binding was also induced by other guanine nucleotides but not by adenine nucleotides. Our results suggest that platelet-activating factor receptor in human neutrophil membranes may be coupled to a guanine nucleotide binding protein.

Adenine Nucleotides↗
PubMed1986

Use of fluoride ion as a probe for the guanine nucleotide-binding protein involved in the phosphoinositide-dependent neutrophil transduction pathway.

Fluoride activation of neutrophils was found to be associated with phosphoinositide turnover, as monitored by the time-dependent accumulation of inositol phosphates. Unlike phosphoinositide turnover induced by the chemotactic peptide, formylmethionylleucylphenylalanine, that induced by fluoride was not inhibited by pretreatment with pertussis toxin. The translocation of protein kinase C activity from the cytosolic to the membrane compartment was also observed in fluoride-stimulated cells. We have proposed that the mode of action of this halide ion involves interaction with a GTP-binding protein which serves as an intermediary unit between the receptors for inflammatory stimuli and the phosphoinositide-specific phosphodiesterase.

Bucladesine↗
PubMed1986

Effect of gold compounds on NADPH oxidase system of human neutrophils.

The inhibitory effects of gold compounds on the NADPH oxidase system of human polymorphonuclear leukocytes (PMNs) has been investigated. Auranofin (0.5-4.0 micrograms Au/ml) suppressed the rate of superoxide anion generation as well as the total yield in cells stimulated with phorbol myristate acetate and f-Met-Leu-Phe. This implies that drug action may be occurring at the level of protein kinase C or steps subsequent to this in the signal transduction sequence. Sodium aurothiomalate (1-100 micrograms Au/ml) lacked such activity. Neither gold compound altered the ability of the granule-rich fraction of PMNs to produce oxy radicals whether this fraction was obtained from drug-treated cells or was treated after its isolation. Therefore, in order for auranofin to exhibit its inhibitory effects on the NADPH oxidase system, an intact cell membrane is necessary.

Auranofin↗
PubMed1986

Positron emission tomography and the possible origins of cytopathology in Alzheimer's disease.

The local cerebral metabolic rate for glucose (LCMRgl), as determined by positron emission tomography (PET), declines in the cerebral cortex in Alzheimer's disease; the severity of the decline parallels the severity of the dementia and correlates with regional cortical neuronal loss and glial proliferation. The cholinergic cells of the medial basal forebrain show a pathological dropout in Alzheimer's disease which accounts for the decline in choline acetyltransferase in the cerebral cortex and hippocampus. It is proposed that these cholinergic cells serve both as an acquisition and readout device for memory; reconstruction of real time events can thus be created in the areas of neocortex where consciousness resides. Alzheimer's disease may have a toxic, genetic or infectious origin; electron microscopic evidence is presented for the possible presence of viral particles of the double stranded DNA type in Alzheimer's brain tissue.

Alzheimer Disease↗
PubMed1986

Conjugational fertility and location of chloramphenicol biosynthesis genes on the chromosomal linkage map of Streptomyces venezuelae.

In Streptomyces venezuelae fertility, defined as chromosomal gene recombination, was enhanced over 1000-fold when one parent in a biparental conjugational cross lacked the physically-undetected plasmid SVP1, as compared with crosses in which both parents carried SVP1. The existence of SVP1 and at least two other fertility plasmids, SVP2 and SVP3, was detected in S. venezuelae by 'lethal zygosis' elicited by a plasmid-plus mycelium in contact with a plasmid-minus mycelium. Conjugational crosses were used to construct a linkage map of S. venezuelae which was highly consistent with the map of analogous loci in S. coelicolor A3(2). A cluster of genes governing chloramphenicol biosynthesis was located near arg, cys and pdxB genes at a position roughly equivalent to the 1-2 o'clock region of the S. coelicolor A3(2) map.

Chloramphenicol↗