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Biomedical subjects

K Y Chan

Publications and source records attributed to K Y Chan.

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

Release of plasminogen activator by cultured corneal epithelial cells during differentiation and wound closure.

The release of plasminogen activator (PA) by corneal epithelium was studied utilizing pure culture of rabbit corneal epithelial cells and a sensitive photometric assay for the enzyme. The activity of PA measured in conditioned medium collected from the cultured cells was plasminogen-dependent, acid-stable, and free of interference by endogenous PA inhibitors. When serum was included in the culture medium, it was necessary to acid-treat the conditioned medium before PA assay in order to inactivate plasma-derived inhibitors. During a month of culture in serum-free medium, the cells released a low basal level of PA in the first week of growth and confluency. During the second week the cells progressively increased PA secretion at the onset of cell differentiation, reaching a peak (18-fold increase) in the third week when focal multilayering of cells occurred. Thereafter, the cells declined release, concomitant with globular aggregation of cells. A delay in the elevated release of PA was observed when the confluent phase was extended to 3 weeks, after which a substantial rise in PA level occurred simultaneously with the onset of multilayering. An in vitro model of corneal wound closure was established on confluent epithelial cells (grown in serum-containing culture medium) by mechanically removing 35-40% of cells in a central circular area. Complete wound closure was effected within 2-4 days by cell migration. The release of PA during the first day of wound closure was four times that of unwounded culture. The results indicated that PA secretion by corneal epithelium was associated with cell differentiation and cytomobility, processes that occur during stratification or wound closure. This conclusion is discussed with respect to a previously hypothesized role of PA in corneal injury and ulceration.

Animals↗
PubMed1986

Occurrence and distribution of halophilic vibrios in subtropical coastal waters of Hong Kong.

The summer occurrence and distribution of halophilic vibrios in the subtropical coastal waters of Hong Kong were investigated. The density of vibrios in six sample sites ranged from 90 to 6,700 per ml, which made up 0.41 to 40% of the total bacterial populations of these sample sites. The sucrose-positive vibrios were found to be much more common (88% of total vibrios) than the sucrose-negative ones. A total of 48 strains belonging to six Vibrio species were fully characterized. Among these, Vibrio alginolyticus was the most frequently isolated, followed by V. parahaemolyticus, V. harveyi, V. vulnificus, V. campbellii, and V. fluvialis. The finding that eight of the nine strains of V. harveyi showed a positive Kanagawa reaction warrants further study.

Hong Kong↗
PubMed1986

Chemical injury to an in vitro ocular system: differential release of plasminogen activator.

Primary cultures of corneal epithelial cells from adult albino rabbits were exposed briefly to various concentrations of NaOH and formaldehyde. The release of plasminogen activator from the cells was stimulated or inhibited during a 6-day recovery period. This differential effect was dependent on the chemical concentration and duration of cell recovery. The modulation of plasminogen activator release in the in vitro system would be useful for predicting ocular toxicity of substances.

Animals↗
PubMed1985

Sensory nerve endings of the incisive papilla of rat hard palate studied by peroxidase cytochemical methods.

This study utilized peroxidase cytochemical methods to survey and analyze the distribution, morphology, and functional relationship of the various components of sensory nerve endings in a focal region of the anterior hard palate (incisive papilla) of the rat. The studies included an anatomical survey of this relatively unknown oral structure, confirmation of the trigeminal origin (labeled by retrograde axonal transport of WGA-HRP injected into the incisive papilla) of the sensory nerve endings, and a complete analysis of the distribution of these nerve endings (labeled by anterograde axonal transport of HRP or WGA-HRP injected into the trigeminal ganglion). Three methods of fixation and two methods of cytochemical reaction were used for selection of an optimal technique for these studies. The results showed distinct patterns of peroxidase-labeled sensory nerve endings at three regions of the incisive papilla: a) dome region (ventral), where labeled nerve endings formed three parallel channels in association with three surface ridges; b) chemosensory corpuscle enriched region (medial to incisive canal), where 82% of the 30-40 chemosensory corpuscles were labeled; and c) lateral labium (lateral to incisive canal), where labeled nerve endings formed a circumscribed network guarding the orifice of incisive canal. The discrete organization of multiple sensory nerve endings in the incisive papilla of the rat may provide an easily accessible model system for various studies in sensory physiology.

Animals↗
PubMed1985

Anterograde axonal transport and intercellular transfer of WGA-HRP in trigeminal-innervated sensory receptors of rat incisive papilla.

The ultrastructure and identification of WGA-HRP-labeled sensory receptors in the rat incisive papilla (the most anterior part of hard palate) were studied using semiserial thin sections. Various sensory receptors were organized according to three locations: dome region (ventral), chemosensory corpuscle region (medial to orifice of incisive canal), and lateral labium (apposing the incisive canal). In the dome region, the sensory receptors were localized in three sensory zones that were associated with surface ridges (one medial and two lateral). In each of these zones, intraepithelial receptor axons and Merkel receptors occurred in the epithelium, while simple unencapsulated corpuscles, glomerular-Meissner corpuscles, and incisive (encapsulated) corpuscles occurred in the lamina propria. In the chemosensory corpuscle region, chemosensory corpuscles and intraepithelial receptor axons were located in the epithelium, and incisive corpuscles were present in the lamina propria. In the lateral labium, only intraepithelial receptor axons were prominent. In all these sensory receptors, the preterminal axons and axon terminals were labeled with the tracer protein. In addition, some nonneuronal cells closely associated with the axon terminals were selectively labeled, e.g., terminal Schwann cells, lamellar Schwann cells, Merkel cells, corpuscular basal cells and chemosensory cells. Other adjacent cells were not labeled, e.g., unspecialized epithelial cells, capsular cells, corpuscular sustentacular cells, and fibroblasts. In both labeled axons and cells, WGA-HRP was incorporated into vesicles, tubules, and vacuolar organelles. The specific intercellular transfer of tracer protein may indicate trophic interactions between axon terminals and support cells in sensory receptors. The specific organization of multiple sensory receptors in the rat incisive papilla may provide a useful alternative system for studying somatosensory physiology.

Animals↗
PubMed1985

Specificity of a neuronotrophic factor from rabbit corneal epithelial cultures.

Previous studies have demonstrated that of the three major cell types of rabbit cornea, only epithelial cells released a neuronotrophic factor that is active in both promoting survival and inducing neurite outgrowth of dissociated trigeminal neurons. In this study, the specificity of neuronotrophic factor production by selected epithelial cell types and the responsiveness of neurons from several different tissues to this trophic factor were determined. Cell cultures of various epithelia and dissociated neurons from several ganglia of neonatal and adult rabbits were utilized. In comparison with adult corneal epithelium, adult bulbar conjunctiva released a similar amount of trophic factor. Neonatal corneal epithelium released five times more, but adult retinal pigment epithelium and neonatal skin epithelium yielded less than a third and one-sixth respectively, and three cell lines (adult skin, kidney and neonatal lens epithelia) released only negligible amounts. Compared with its effect on neonatal trigeminal neurons, the trophic factor from adult corneal epithelium was similarly active on neonatal dorsal root neurons, but only half as effective on adult trigeminal neurons and less than one-tenth as effective on neonatal superior cervical neurons. The effect of nerve growth factor (from mouse submaxillary gland) on these neurons was tested for comparison. The results indicated that of the tissues studied, neuronotrophic factor was released in abundance only from corneal and conjunctival epithelia, and was active predominantly on trigeminal and dorsal root neurons (sensory neurons). This is consistent with the concept that the developmentally regulated release of trophic factor by target cells may be an underlying mechanism for neurogenesis and nerve regeneration.

Aging↗
PubMed1985

Bacteria in bivalve shellfish with special reference to the oyster.

The bacterial flora of the Pacific oyster Crassostrea gigas, the sea mussel Perna viridis and the arkshell clam Scapharca cornea differed considerably from that of seawater in both numbers and generic composition. The numbers of heterotrophic bacteria in the bivalve shellfish, including the anaerobes and spore-forming bacteria, were greater than that in the surrounding water. Pseudomonas spp. were the dominant organisms, comprising over one third of the 321 strains characterized after isolation from the bivalves and seawater. Other bacteria isolated from the shellfish included Vibrio, Acinetobacter, and Aeromonas spp., whereas the seawater flora consisted mainly of coliform organisms, coryneform bacteria and Flavobacterium/Cytophaga spp. Bacteria associated with the deposit-feeding clams were higher in density and more distinct in generic composition as compared with those in the suspension-feeding oysters and mussels. Over 90% of the coliform and heterotrophic bacteria in oysters were found in organs associated with the digestive tract. Coliforms were mainly found in the stomach while heterotrophs were present in both stomach and the lower intestine. The results suggest that the stomach flora of oysters are mainly derived from the external environment and, through a process of selection and multiplication, that it may be gradually replaced by a more indigenous population which dominates the lower digestive tract.

Animals↗
PubMed1985

Anorectal malformations and their associated anomalies.

Congenital malformation of the rectum and anus is a problem frequently encountered in the neonatal period. 88 patients presenting with anorectal malformations were analysed and physical, operative, radiological and autopsy findings were reviewed to determine the types and incidence of associated lesions. Genitourinary malformations form the major group of associated lesions and contribute a significant degree of morbidity in the overall management of the anorectal deformities.

Abnormalities, Multiple↗
PubMed1984

Simultaneous analysis of a new cardiotonic agent, MDL 17,043, and its major sulfoxide metabolite in plasma by high-performance liquid chromatography.

MDL 17,043 or 1,3-dihydro-4-methyl-5-[4-(methylthio)benzoyl]-2H-imidazol-2-one, is a new cardiotonic agent being developed for the treatment of congestive heart failure. This communication describes a sensitive and selective analytical procedure for the simultaneous analysis of MDL 17,043 and its major oxidative metabolite in plasma. The method involves addition of internal standard and organic solvent extraction, followed by separation with high-performance liquid chromatography and detection by ultraviolet absorption. The assay has good precision and accuracy. Evidence for the positive identification of the sulfoxide metabolite is also presented.

Cardiotonic Agents↗
PubMed1984

Physiological responses of Bacillus species to concanavalin A. 2. Effect on growth, oxygen uptake, enzyme activities and intracellular cyclic guanosine 3',5'-monophosphate level of B. cereus ATCC 14579.

The effect of the mitogen concanavalin A (Con A) on growth and several physiological aspects of Bacillus cereus ATCC 14579 was investigated. Con A at concentrations ranging from 50 to 750 micrograms/ml stimulated growth (the growth rate increased from 0.52/h to 0.97/h, and final yield increased by 2.3-fold over the control) of the bacterial cells. Con A-treated cells also increased their oxygen uptake (1.6-fold increase when treated with 750 micrograms/ml of Con A). The activities of the membrane-bound dehydrogenase and phosphatase increased by 1.75-fold and 2.1-fold, respectively, when treated with 500 micrograms/ml of Con A. However, only a one-fold increase in alpha-glucosidase activity was observed when cells were treated with the same concentration of Con A. Con A at concentrations of 500 to 1,000 micrograms/ml stimulated the cellular synthesis of cyclic guanosine 3',5'-monophosphate (cGMP) by one-fold. It is proposed that binding of Con A to the cell envelope led to increased synthesis of cGMP which might serve as an intracellular messenger for expression of the mitogenic signal of Con A. Since the use of 50 mg/ml of alpha-methyl-D-mannopyranoside (alpha-MM), a Con A inhibitor, could reverse the stimulatory effect of Con A, it was obvious that the stimulatory action was initiated by the specific binding of Con A molecules to the cell envelope. Furthermore, the stimulatory effect was found to be Con A dosage dependent.

Bacillus cereus↗
PubMed1983

Quantitative analysis of melperone in human plasma by gas chromatography--mass spectrometry--selected ion monitoring.

A sensitive, specific and reliable assay utilizing a combined gas chromatography--mass spectrometry--selected ion monitoring technique is described for the quantitative determination of melperone, a neuroleptic agent, in human plasma. Using a 2-ml plasma sample, the method is sensitive and has acceptable precision in the range of 1 to 100 ng/ml. The method is applied in a limited bioavailability study and found to be adequate. A plasma metabolite was isolated and identified in the clinical samples.

Antipsychotic Agents↗
PubMed1983

Epithelial-stromal interactions: specific stimulation of corneal epithelial cell growth in vitro by a factor(s) from cultured stromal fibroblasts.

By using a recently modified method of isolating and culturing rabbit corneal cells, this study investigated the presence of a diffusible substance(s) in stromal fibroblast conditioned medium that stimulated the growth of cultured corneal epithelial cells. The growth stimulation involved initiation of DNA synthesis (assayed by [3H]-thymidine incorporation) and enhanced cell proliferation (quantified by cell counting). Among the three corneal cell types, only fibroblasts (rabbit and human) released the stimulatory substance, which acted only on epithelial cells. The effect of this stromal fibroblast factor (SFF) was observed after an exposure period of less than 16 hr and persisted as long as it was present. Its action was concentration-dependent and was not a result of improvement in the survival of epithelial cells during culture. Both sparse and confluent epithelial cultures were susceptible to SFF. The release of SFF was correlated with the number of fibroblasts in the culture and appeared to be sensitive to the growth condition of the cells. Both the release and action of SFF did not depend on the presence of serum in the culture medium. The factor was heat resistant and insensitive to proteolytic enzymes. From ultrafiltration studies, the size of SFF was estimated to be in the approximate range of 50-1000 daltons. By direct comparison of the stimulatory effect with other previously studied growth promoting agents, it was concluded that SFF was not epidermal growth factor, fibroblast growth factor, putrescine, cyclic AMP, hydrocortisone or acetate. The implication of SFF in the regulation of epithelial growth by endogenous, intercellular mechanisms is discussed.

Animals↗
PubMed1983

Production and properties of alpha-glucosidase from Lactobacillus acidophilus.

Lactobacillus acidophilus IFO 3532 was found to produce only intracellular alpha-glucosidase (alpha-D-glucoside glucohydrolase; EC 3.2.1.20). Maximum enzyme production was obtained in a medium containing 2% maltose as inducer at 37 degrees C and at an initial pH of 6.5. The enzyme was formed in the cytoplasm and accumulated as a large pool during the logarithmic growth phase. Enzyme production was strongly inhibited by 4 microM CuSO4, 40 microM CoCl2, and beef extract; MnSO4 and the presence of proteose peptone and yeast extract in the medium greatly enhanced enzyme production. A 16.6-fold purification of alpha-glucosidase was achieved by (NH4)2SO4 fractionation and DEAE-cellulose column chromatography. The enzyme showed high specificity for maltose. The Km for alpha-p-nitrophenyl-beta-D-glucopyranoside was 11.5 mM, and the Vmax for alpha-p-nitrophenyl-beta-D-glucopyranoside hydrolysis was 12.99 mumol/min per mg of protein. The optimal pH and temperature for enzyme activity were 5.0 and 37 degrees C, respectively. The enzyme activity was inhibited by Hg2+, Cu2+, Ni2+, Zn2+, Ca2+, Co2+, urea, rose bengal, and 2-iodoacetamide, whereas Mn2+, Mg2+, L-cysteine, L-histidine, Tris, and EDTA stimulated enzyme activity. Transglucosylase activity was present in the partially purified enzyme, and isomaltose was the only glucosyltransferase product. Amylase activity in the purified preparation was relatively weak, and no isomaltase activity was detected.

Carbohydrates↗
PubMed1982

Isolation and culture of corneal cells and their interactions with dissociated trigeminal neurons.

The three cell types of rabbit cornea (epithelium, stromal fibroblasts and endothelium) were isolated by an improved method using both microdissection and selective enzyme treatment. This technique reproducibly resulted in an almost total recovery of each cell type from a given cornea. When maintained in culture, the three cell types showed different morphologic characteristics, each resembling the in vivo counterpart. The epithelial culture consisted of both attached and floating cells. The attached cells located at the marginal area of a colony were irregular in shape and possessed pseudopodia, while those in the confluent area were polygonal. Floating cells were typically vacuolated, curve-shaped and joined in groups of 2-4 cells as a spherical body enclosing a lucent interior. Comparison of mitotic rates, ultrastructure, keratin levels and other cytologic evidence suggested that the attached cells may correspond to the basal cells and less differentiated wing cells, while the floating cells may be analogous to the more differentiated wing cells and superficial cells. Neurons dissociated from neonatal rabbit trigeminal (Gasserian) ganglia were plated into multiwells partially covered with a given corneal cell type. The percentages of viable and neurite-bearing neurons were evaluated on the first three days. When neurons were grown in contact with each of the corneal cell types, neurites were extended in every case. However, when neurons were not in contact with the corneal cells in the coculture, only epithelial cells permitted neurite outgrowth. The data suggested two types of cellular interactions between corneal cells and sensory neurons, one of which may be the specific release of a neuronotrophic factor by epithelial cells. This culture system represents the first step towards developing an in vitro model for studying various cornea-trigeminal interactions.

Animals↗
PubMed1982

Metabolic disposition of terfenadine in laboratory animals.

Alpha-[4-(1,1-Dimethylethyl)phenyl]-4-(hydroxydiphenylmethyl)-1- piperidinebutanol (terfenadine, RMI 9918, Triludan, Teldane, resp.), a clinically effective antihistamine, with little or no central nervous system effects, was investigated in order to understand its metabolic disposition. These 14C-terfenadine studies were performed in laboratory animals, principally the rat, and also in beagle dog and monkey (Macaca mulatta). In all three species the fecal pathway of excretion was predominant with nearly all the elimination occurring within 24 h of administration. The data suggest that biliary excretion plays a prominent role. Tissue distribution studies indicated that the liver and lung, relative to other tissues, exhibited the highest concentrations of 14C-terfenadine equivalents. However, brain had low amounts of 14C-terfenadine which was in general agreement with the whole-body autoradiographic studies which did not show radioactivity in brain or spinal cord. The evidence suggests that terfenadine was metabolized rapidly with no terfenadine in urine or bile and small amounts in feces. Tissue concentrations of terfenadine were in the low nanogram range and peaked at 0.5-1.0 h with lung exhibiting the greatest and the brain sub-quantifiable amounts. The ratios of 14C-terfenadine eq/terfenadine were high and greatest in the liver and kidney. These studies demonstrated that terfenadine was readily absorbed and eliminated, virtually had undergone complete biotransformation and exhibited very low tissue concentrations per se.

Animals↗