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Biomedical subjects

K Park

Publications and source records attributed to K Park.

At least 271 records · Page 15Linked to original sources
PubMed1997

A modified hearing aid fitting procedure using both real ear and 2cc coupler measurement system.

In order to reduce the test time in real ear hearing-aid fitting for children, the validity of applying the average real ear to coupler differences (RECDs) in prefitting procedure using a 2cc coupler measurement system was evaluated by checking whether the majority of people's RECDs might occur within 5 dB of the average RECDs (N = 116) in each test frequency and age group. The percentages of occurrence were around 90% in test subjects' RECDs in saturation sound pressure levels (SSPLs) and around 70% in gain in each important test frequency. Appropriate test frequencies in prefitting are 500, 1000, 1500 and 2000 Hz.

Adolescent↗
PubMed1997

Relationship between cavernosal ischemia and corporal veno-occlusive dysfunction in an animal model.

PURPOSE: It has been postulated that cavernosal tissue ischemia secondary to arterial occlusive disease is associated with corporal veno-occlusive dysfunction. The goal was to correlate, for the first time, direct local intracavernosal blood flow measurements as a measure of cavernosal tissue perfusion with the integrity of corporal veno-occlusion in an animal model of vasculogenic impotence. MATERIALS AND METHODS: The New Zealand White rabbit model of vasculogenic impotence was utilized (7 control, 9 atherosclerotic). After 16 weeks, intracavernosal blood flow was recorded directly by laser Doppler flowmetry. The relationships among peak intracavernosal blood flow, equilibrium intracavernosal pressure and corporal veno-occlusive function (as determined by intracavernosal pressure decay) were examined. RESULTS: Significant differences in the atherosclerotic compared to control animals were noted in iliac artery blood flow (12 +/- 4 vs 31 +/- 7 ml./min.), peak intracavernosal blood flow during erection (16 +/- 7 vs 25 +/- 4 ml./min./100 gm. tissue), equilibrium intracavernosal pressure (48 +/- 11 vs 72 +/- 6 mm. Hg) and intracavernosal pressure decay (57 +/- 17 vs 36 +/- 8 mm. Hg). Peak intracavernosal blood flow during erection was found significantly related to both equilibrium pressure (r = 0.75) and cavernosal pressure decay (r = -0.8). CONCLUSIONS: Abnormal intracavernosal blood flow (cavernosal ischemia) secondary to arterial occlusive disease predicts abnormal veno-occlusive function and poor erection quality.

Animals↗
PubMed1997

Results of kidney transplantation from 1979 to 1997 at Yonsei University.

1. Long-term graft survival markedly improved after the introduction of CsA as the main immunosuppressant in living-donor kidney transplantation at our institution. 2. HLA-identical LRD kidney transplantation provided the best long-term graft survival rate, probably due to a decreased incidence of graft loss from rejection. 3. We could achieve good long-term graft survival in LURD kidney transplantation compared with that of HLA-haploidentical LRD kidney transplantation. 4. Because of the striking discrepancy between organ donation and the increasing demand for transplantation, distant relative donors and LURDs, including swap donors, should be considered as an alternative way to increase the number of available donors when accompanied by a careful evaluation process.

Adolescent↗
PubMed1996

The organic crystallizing agent 2-methyl-2,4-pentanediol reduces DNA curvature by means of structural changes in A-tracts.

Contemporary predictive models for sequence-dependent DNA structure provide a good estimation of overall DNA curvature in most cases. However, the two current models differ fundamentally in their view of the origin of DNA curvature. An earlier model that associates DNA bending primarily, although not exclusively, with stretches of adenines (A-tracts) is based on results of comparative gel retardation, cyclization kinetics, hydroxyl radical cutting, and other solution measurements. It represents an intersection of wedge and junction models. More recently, a non-A-tract bending model has been proposed, built on structural results from x-ray crystallography and molecular modeling. In this view, A-tracts are proposed to be straight and rigid, whereas mixed sequence DNA is bent. Because a key premise of the non-A-tract bending model is the crystallographic observation that A-tracts are straight, we have examined the effect in solution of 2-methyl-2,4-pentanediol (MPD), an organic solvent used in crystal preparation for crystallographic DNA structure determinations. Using cyclization analysis, DNase I cutting, chemical probing, and electron microscopy on DNA oligomers with and without A-tracts, we show that the presence of MPD in solution dramatically affects A-tracts and that the effect is specific to these sequence elements. Combined with the previous observation that MPD affects gel mobility of curved sequences with A-tracts, our findings support the bent A-tract model and call for caution in the interpretation of crystallographic results on DNA structure as these are presently obtained.

Artifacts↗
PubMed1996

Three distinct chloride channels control anion movements in rat parotid acinar cells.

1. We used the whole-cell configuration of the patch clamp technique to examine the different macroscopic Cl- currents present in single rat parotid acinar cells. 2. Cell swelling produced by negative osmotic pressure (hypotonic bath solutions) induced a large outwardly rectifying Cl- current with little or no time and voltage dependence. In contrast, an increase in intracellular [Ca2+] induced by ionomycin activated Cl- currents with very different properties. Ca(2+)-activated Cl- currents showed outward rectification, relatively slow activation kinetics and marked voltage dependence. These results are consistent with the existence of two different outwardly rectifying Cl- channels in rat parotid cells. 3. In conditions designed to eliminate the activation of these two Cl- currents, a third type of current was observed. This third current was activated in a time-dependent manner by hyperpolarized potentials and was about equally permeant to Cl-, I- and Br-. 4. The properties of the hyperpolarization-activated current were similar to those of the cloned ClC-2 channel. Polymerase chain reaction-based methods and ribonuclease protection analyses indicated the presence in parotid gland of mRNA homologous to ClC-2. 5. Individual parotid acinar cells expressed all three types of Cl- channels. Each type of channel may contribute to Cl- efflux in distinct stages of the secretion process depending on the intracellular [Ca2+], cell volume and membrane potential.

Animals↗
PubMed1996

Regulation of transforming growth factor-beta 1 expression by the hepatitis B virus (HBV) X transactivator. Role in HBV pathogenesis.

TGF-beta 1 has been implicated in the pathogenesis of liver disease. The high frequency of detection of the hepatitis B virus X (HBx) antigen in liver cells from patients with chronic hepatitis, cirrhosis, and liver cancer suggested that expression of HBx and TGF-beta 1 may be associated. To test this possibility, we examined the expression of TGF-beta 1 in the liver of transgenic mice expressing the HBx gene. We show that the patterns of expression of TGF-beta 1 and Hbx protein are similar in these mice and that HBx activates transcription of the TGF-beta 1 gene in transfected hepatoma cells. The cis-acting element within the TGF-beta 1 gene that is responsive to regulation by Hbx is the binding site for the Egr family of transcription factors. We further show that the Egr-1 protein associates with the HBx protein, allowing HBx to participate in the transcriptional regulation of immediate-early genes. Our results suggest that expression of Hbx might induce expression of TGF-beta 1 in the early stages of infection and raise the possibility that TGF-beta 1 may play a role in hepatitis B virus pathogenesis.

Amino Acid Sequence↗
PubMed1996

Characterization of glucose dependent gel-sol phase transition of the polymeric glucose-concanavalin A hydrogel system.

PURPOSE: The main goal of this study was to synthesize and characterize hydrogels which undergo reversible gel-sol phase transformation in response to changes in glucose concentration in the surrounding environment. METHODS: The glucose-sensitive hydrogels were made by mixing the appropriate concentrations of acrylamide-allyl glucose copolymer and concanavalin A (Con A). To examine their phase reversibility, hydrogels in dialysis membranes were cycled between glucose-free and glucose-containing buffers. The binding affinity of allyl glucose (AG) to Con A was examined by using an equilibrium dialysis technique. RESULTS: The synthesized hydrogels underwent phase transition to sol in the presence of free glucose in the environment. The concentration of external free glucose (Cf) had to be at least 4 times that of polymer-bound glucose (Cp) to induce phase transition from gel to sol. The binding affinity study showed that binding of AG to Con A was four times stronger than that of free glucose. When Cp in the gel was 0.42 mg/ml or higher, Cf had to be much higher than 4 times Cp to induce phase transition. CONCLUSIONS: The synthesized hydrogels underwent phase transition in the presence of free glucose in the environment, but the phase transition was not linearly dependent on the concentration of free glucose. This non-linear dependence was explained by the increased binding affinity of AG over native glucose to Con A, and the cooperative interactions between polymer-bound glucose and Con A.

Binding Sites↗
PubMed1996

Dissociation kinetics of RepA dimers: implications for mechanisms of activation of DNA binding by chaperones.

BACKGROUND: The replication initiator of plasmid P1, RepA, binds DNA as monomer. The binding is stimulated by the chaperones DnaJ, DnaK and GrpE of Escherichia coli. Two models of chaperone action have been proposed. (i) Chaperones dissociate RepA dimers, which are inactive in DNA binding, into active monomers. (ii) The dissociation occurs spontaneously but the monomeric products require the chaperones for refolding into the active form. The latter model was based on the observation that RepA diluted 1000-fold below the K(D) for dimer dissociation, still required the chaperones for DNA binding. RESULTS: We have confirmed that under the condition of DNA binding experiments, the RepA dimers dissociate reversibly into monomers with a K(D) value of 1.1 +/- 0.1 microM. In the vicinity of this concentration, the sedimentation coefficient of RepA was concentration dependent, allowing estimation of s(20,w) coefficients for the RepA monomer (2.95 S) and dimer (4.01 S). Dynamic light scattering experiments indicated an increase of the monomer fraction within 5 min of RepA dilution. Circular dichroism (CD) measurements were consistent with these results. CONCLUSION: RepA monomerization is efficient without the mediation of chaperones. They are required to activate RepA most likely because they are needed to re-fold RepA monomers.

Circular Dichroism↗
PubMed1996

Oral immunization of rabbits against Pasteurella multocida with an alginate microsphere delivery system.

Oral delivery of microencapsulated antigens is a potential means to vaccinate rabbits against Pasteurella multocida, a common bacterial pathogen. Groups of five rabbits were dosed orally on days 0, 7, and 14 with alginate microspheres prepared to contain no added protein, 5 mg of a potassium thiocyanate extract of P. multocida (PTE), or 5 mg of PTE with 200 micrograms of cholera toxin (CT). In addition, groups were dosed orally with 5 mg of soluble PTE with or without 200 micrograms CT, intranasally (IN) with 1 mg of soluble PTE, or with saline. Serum and nasal lavage samples collected prior to initial immunization and 10, 16, and 21 days later were assayed by ELISA for anti-PTE IgG and IgA. Strong nasal lavage IgA and serum IgG activities were found in samples from rabbits immunized with PTE IN or orally when incorporated into microspheres. Addition of CT did not significantly enhance either response. To examine the development of protective immunity, groups were similarly immunized and challenge-exposed IN on day 16 with 10(6) CFU of P. multocida. One week later, rabbits were euthanized, and specimens from the lungs, nasopharynx, liver, and inner ear were cultured for P. multocida. Less severe infections of the lung and nasopharynx developed in rabbits immunized with PTE IN or orally in microspheres, with or without added CT. In addition, culture of liver and tympanic bullae samples from these rabbits yielded growth of P. multocida less frequently compared to other P. multocida-challenged rabbits. Coadministration of CT and PTE did not significantly improve protective immunity to challenge.

Adjuvants, Immunologic↗
PubMed1996

Platelet interactions with plasma-polymerized ethylene oxide and N-vinyl-2-pyrrolidone films and linear poly(ethylene oxide) layer.

Dimethyldichlorosilane (DDS)-treated glass (DDS-glass) was modified with either poly(ethylene oxide) (PEO) films or poly(N-vinyl-2-pyrrolidone) (PNVP) films by plasma polymerization. The thickness of the plasma polymerized films was varied between 40 and 700 nm. The results showed that the hydrophilic plasma polymerized PEO and PNVP films on DDS-glass did not prevent platelet adhesion and activation. The film thickness had only marginal influence on the prevention of platelet activation. In contrast, platelet adhesion was prevented on DDS-glass absorbed with a PEO-containing block copolymer (Pluronic F-108 surfactant) even at a calculated thickness of the PEO layer of less than 40 nm. This study shows that surface hydrophilization is not sufficient for prevention of platelet adhesion and activation. The contrasting results in platelet adhesion between cross-linked plasma polymers and linear PEO-containing block copolymers may be explained qualitatively by a steric repulsion mechanism that is achieved by the conformational freedom of the linear PEO chains interacting with water.

Biocompatible Materials↗
PubMed1996

Biological activity of brain-derived neurotrophic factor with mismatched disulfide linkages produced by Escherichia coli.

E. coli cells harboring an expression plasmid with a brain-derived neurotrophic factor (BDNF) gene obtained from rat BDNF cDNA were sonicated and centrifuged to obtain a precipitate containing BDNF. Ten different proteins of BDNF were purified from the precipitate and the three disulfide linkages of six proteins were identified. Those disulfide structures were different from that of authentic BDNF and the biological activities of BDNF with mismatched disulfide linkages (EC50 of 2 to 15 ng/ml) were much lower than that of authentic BDNF (EC50 of 30 pg/ml). The BDNF with mismatched disulfide linkages inhibited the biological activity of authentic BDNF.

Animals↗
PubMed1996

Establishment of primary cell culture from stria vascularis explants. Morphological and functional characterization.

To provide the prerequisite for long-term study of the inner ear related to structural and functional integrity, tissue of stria vascularis with spiral ligament was isolated from Wistar rat cochleas and cultured using the explant-culture technique. The following culture media were used: EMEM with Hepes buffer, hydrocortisone (400 ng/ml), transferrin (5 micrograms/ml). triiodothyronine (10(-9) M), cholera toxin (10(-10) M), insulin (5 micrograms/ml), and epidermal growth factor (10 ng/ml). To characterize the cells growing out from the explant, immunofluorescence with cytokeratin (cytokeratin 18) and ultrastructural examination with SEM and TEM were performed. The marginal cell function was investigated by expression of Na+, K(+)-ATPase antisera against beta 2 subunit of rat Na+, K(+)-ATPase and P-NPPase. We were able to maintain the cultured cells for 3 weeks or more. Monolayered marginal cells were observed beyond 14 days in vitro and the expression of cytokeratin 18 was especially enhanced. The cultured marginal cells were almost identical to in vivo cells both as regards ultrastructural features and Na+, K(+)-ATPase activity. The present results suggest that the primary explant culture technique is a reliable in vitro model of strial marginal cells. However, establishment of the cell line is needed for long-term study.

Animals↗
PubMed1996

The role of an open-access bleeding unit in the management of colonic haemorrhage. A 2-year prospective study.

BACKGROUND: Major colonic haemorrhage poses difficult diagnostic and therapeutic problems and, in contrast to upper gastrointestinal bleeding, has no generally accepted plan of management. METHODS: We report community-based prospective data accumulated over 2 years (1991-93) on 1602 patients referred to an open-access bleeding unit with suspected gastrointestinal haemorrhage. RESULTS: Of 278 (17%) admissions with suspected lower GI haemorrhage, 252 were confirmed. Forty-eight per cent were defined as "significant' bleeds, with a decrease in haemoglobin and cardiovascular compromise. Of 102 significant bleeds in subjects more than 60 years old, 29% rebled, and 12.6% required emergency surgery. Diverticular disease (24%) was the commonest diagnosis, with tumours, infective colitis, and inflammatory colitis each at 10%. The overall 30-day mortality for colonic bleeding was 5.1% (13 of 252), with only 1 death occurring in the group less than 60 years old. CONCLUSIONS: This study provides a unique database for the natural history of colonic bleeding and its management within the setting of a specialized bleeding unit.

Adult↗
PubMed1996

Interstitial mononuclear cell infiltrates in chronic rejection of the kidney and correlation with peripheral blood.

To investigate the characteristics of interstitial inflammatory cells and possible involvement of nudelta T cells, 16 renal allograft biopsies showing chronic rejection were stained by immunohistochemical method and correlated with the data of peripheral blood evaluated by flow cytometry. For immunophenotyping, fresh frozen sections were stained with monoclonal antibodies against CD3, CD4, CD8, CD68, CD56, TCRdelta1 and HLA DR. Paraffin embedded tissue was stained with CD45RO, CD20-Cy and CD68. Nine cases of nonspecific tubulointerstitial change and 4 cases of nonallograft tubulointerstitial nephritis were used as a control. Inflammatory infiltration was present in all cases studied. T cells predominated in the interstitium of chronic rejection and were followed by macrophages and B cells. The degree of interstitial infiltration of frozen section was not accordant with that of paraffin sections. Allografts with nonspecific tubulointerstitial changes or tubulointerstitial nephritis of native kidneys showed similar distribution pattern in terms of type and degree. However, the degree of infiltrate did not give any statistical significance among groups. The CD4/CD8 ratios in interstitial infiltrates were less than 1.0 in 6 cases and was not accordant with those of peripheral blood. Proportion of nudelta T cells increased over 10% in 2 cases in tissue and in 3 cases in peripheral blood. In 3 cases of chronic rejection in which both tissue and blood results were available, there was no concordance of CD4/CD8 or nudeltaT/CD3 between them. Tubular expression of HLA DR was, however, present only in 4 cases of chronic rejection. In conclusion, T lymphocytes were predominant regardless of diagnosis or disease activity. T lymphocyte subset did not give any suggestion as to the diagnosis or disease activity in chronic rejection. Furthermore nudelta T cells had only limited value. Lymphocytic subsets in peripheral blood would not be predictors of tissue destruction in chronic rejection.

Flow Cytometry↗