PubMed Health⌕ Search

Biomedical subjects

H Nam

Publications and source records attributed to H Nam.

At least 19 recordsLinked to original sources
PubMed2001

A planar amperometric creatinine biosensor employing an insoluble oxidizing agent for removing redox-active interferences.

A planar microchip-based creatinine biosensor employing an oxidizing layer (e.g., a PbO2 film), where interfering redox-active substances are broken (i.e., oxidized) to redox-inactive products, was developed to facilitate the microfabrication of the sensor and to provide improved, reliable determination of creatinine in physiological samples. The feasibility of using hydrophilic polyurethanes in permselective barrier membranes for creatinine biosensors and the effect of adding a silanizing agent (adhesion promoter) on the sensor performance (e.g., sensitivity, stability, and lifetime) are described. The proposed creatinine microsensor with a three-layer configuration, i.e., enzyme, protecting, and oxidizing layers, exhibits good electrochemical performance in terms of response time (t95% = 98 s at 100-->200 microM creatinine change), linearity (1-1000 microM, r = 0.9997), detection limit (0.8 microM), and lifetime (approximately 35 days). The creatinine biosensor devised in a differential sensing arrangement that compensates the erroneous results from creatine is considered to be suitable for assay of serum specimens.

Biosensing Techniques↗
PubMed2001

Ineffective erythropoiesis in Stat5a(-/-)5b(-/-) mice due to decreased survival of early erythroblasts.

Erythropoietin (Epo) controls red cell production in the basal state and during stress. Epo binding to its receptor, EpoR, on erythroid progenitors leads to rapid activation of the transcription factor Stat5. Previously, fetal anemia and increased apoptosis of fetal liver erythroid progenitors were found in Stat5a(-/-)5b(-/-) mice. However, the role of Stat5 in adult erythropoiesis was not clear. The present study shows that some adult Stat5a(-/-)5b(-/-) mice have a near-normal hematocrit but are deficient in generating high erythropoietic rates in response to stress. Further, many adult Stat5a(-/-)5b(-/-) mice have persistent anemia despite a marked compensatory expansion in their erythropoietic tissue. Analysis of erythroblast maturation in Stat5a(-/-)5b(-/-) hematopoietic tissue shows a dramatic increase in early erythroblast numbers, but these fail to progress in differentiation. Decreased expression of bcl-x(L) and increased apoptosis in Stat5a(-/-)5b(-/-) early erythroblasts correlate with the degree of anemia. Hence, Stat5 controls a rate-determining step regulating early erythroblast survival.

Anemia↗
PubMed2001

Ligand-independent oligomerization of cell-surface erythropoietin receptor is mediated by the transmembrane domain.

Binding of erythropoietin (Epo) to the Epo receptor (EpoR) is crucial for production of mature red cells. Although it is well established that the Epo-bound EpoR is a dimer, it is not clear whether, in the absence of ligand, the intact EpoR is a monomer or oligomer. Using antibody-mediated immunofluorescence copatching (oligomerizing) of epitope-tagged receptors at the surface of live cells, we show herein that a major fraction of the full-length murine EpoR exists as preformed dimers/oligomers in BOSC cells, which are human embryo kidney 293T-derived cells. This observed oligomerization is specific because, under the same conditions, epitope-tagged EpoR did not oligomerize with several other tagged receptors (thrombopoietin receptor, transforming growth factor beta receptor type II, or prolactin receptor). Strikingly, the EpoR transmembrane (TM) domain but not the extracellular or intracellular domains enabled the prolactin receptor to copatch with EpoR. Preformed EpoR oligomers are not constitutively active and Epo binding was required to induce signaling. In contrast to tyrosine kinase receptors (e.g., insulin receptor), which cannot signal when their TM domain is replaced by the strongly dimerizing TM domain of glycophorin A, the EpoR could tolerate the replacement of its TM domain with that of glycophorin A and retained signaling. We propose a model in which TM domain-induced dimerization maintains unliganded EpoR in an inactive state that can readily be switched to an active state by physiologic levels of Epo.

Amino Acid Sequence↗
PubMed2001

The erythropoietin receptor cytosolic juxtamembrane domain contains an essential, precisely oriented, hydrophobic motif.

We report that the erythropoietin receptor cytosolic juxtamembrane region is conformationally rigid and contains a hydrophobic motif, composed of residues L253, I257, and W258, that is crucial for Janus kinase 2 (JAK2) activation and receptor signaling. Alanine insertion mutagenesis shows that the orientation of this motif and not its distance from the membrane bilayer is critical. Intragenic complementation studies suggest that L253 is contained within an alpha helix functionally continuous to the transmembrane alpha helix. The alpha-helical orientation of L53 is required not for JAK2 activation but for activated JAK2 to induce phosphorylation of the erythropoietin receptor. This motif is highly conserved among cytokine receptors and couples ligand-induced conformational changes in the receptor to intracellular activation of JAK2.

Amino Acid Motifs↗
PubMed2001

Effect of pre-treatment on the surface and electrochemical properties of screen-printed carbon paste electrodes.

The effect of various electrochemical pre-treatment methods on the surface and electrochemical properties of screen-printed carbon paste electrodes (SPCE) prepared with three different commercial products was examined. It was observed that a positively charged redox couple, e.g., hexaammineruthenium(III), exhibited quasi-reversible behavior at the untreated SPCE. However, the cyclic voltammograms (CVs) of the SPCE prepared with general-purpose carbon inks did not exhibit clear redox peaks to other representative redox couples [e.g., hexacyanoferrate(III), hexachloroiridate(IV), dopamine, and hydroquinone] without activation. Electrochemical pre-treatment methods were sought in four different aqueous solutions, i.e., sulfuric acid, potassium chloride, sodium hydrogencarbonate, and sodium carbonate, applying various activation potentials. It was found that the pre-treatment procedure in saturated Na2CO3 solution at 1.2 V provides a mild and effective condition for activating the SPCE. By measuring the water contact angles at the SPCE surfaces and recording their SEM images, it was confirmed that the electrochemical pre-treatment effectively removes the organic binders from the surface carbon particles. A prolonged period of activation (> 5 min) or the use of high potentials (> 1.2 V) increased the capacitance of the electrode over 20 microF cm(-2). The pre-treated SPCE behaved like a random array microelectrode, exhibiting a sigmoidal-shaped CV at a slow scan rate. The short pre-anodization method in Na2CO3 solution was generally applicable to most SPCE prepared with general-purpose carbon inks.

Journal Article↗
PubMed2001

Effect of dissolved CO2 on the potential stability of all-solid-state ion-selective electrodes.

The influence of dissolved CO2 on the potentiometric responses of all-solid-state ion-selective electrodes (ISEs) was systematically examined with four different types of electrodes fabricated by pairing pH-sensitive and pH-insensitive metal electrodes (Pt and Ag/AgCl, respectively) with pH-sensitive and pH-insensitive ion-selective membranes (H+-selective membrane based on tridodecylamine and Na+-selective membrane based on tetraethyl calix[4]arenetetraacetate, respectively). The experimental results clearly showed that the carbonic acid formed by the diffused CO2 and water vapor at the membrane/metal electrode interface varies the phase boundary potentials both at the inner side of the H+-selective membrane (deltaE(in)mem) and at the metal electrode surface (deltaEelec). The potential changes, deltaE(in)mem and deltaEelec, occurring at the facing boundaries, are opposite in their sign and result in a canceling effect if both the membrane and metal surface are pH-sensitive. Consequently, the H+-selective membrane coated on a pH-sensitive electrode (Pt) tends to exhibit a smaller CO2 interference than that on a pH-insensitive electrode (Ag/AgCl). When the all-solid-state Na+ and K+ ISEs were fabricated with both pH-insensitive metal electrode and ion-selective membrane, they did not suffer from CO2 interference. It was also confirmed that plasticization of the PVC leads to increased CO2 permeation. Various types of intermediate layers were examined to reduce the CO2 interference problem in the fabrication of H+-selective all-solid-state ISEs. The results indicated that the H+-selective electrode needs an intermediate layer that maintains a constant pH unless the carbonic acid formation at the interfacial area is effectively quenched.

Journal Article↗
PubMed2001

Encephalitis associated with motor polyneuropathy.

We describe three patients with acute encephalitis and motor-dominant polyneuropathy. All three patients were in their middle age and presented with features of encephalopathy with flu like illness. Cerebrospinal fluid (CSF) studies showed lymphocytic pleocytosis with increased protein. Brain magnetic resonance imagings (MRIs) showed symmetric high signal intensities in bilateral mesial temporal lobes and bilateral thalami in all patients. All three patients became quadriplegic and areflexic within two hospital days (HDs) and electrophysiologic studies revealed motor polyneuropathy. Viral or atypical bacterial infection was suspected, but no causative agent could be found. One patient expired on the twentieth hospital day, and the other two patients showed no or little improvement. To our knowledge, this combination of acute encephalitis with motor polyneuropathy has not been reported.

Adult↗
PubMed2001

Incidence and clinical profile of extra-medial-temporal epilepsy with hippocampal atrophy.

We tried to investigate the incidence and the clinical profile of intractable epilepsy with hippocampal atrophy and ictal onset zones located in areas other than the hippocampus (extra-medial-temporal epilepsy; EMTE). We included patients who had hippocampal atrophy confirmed by MRI but with extra-medial-temporal ictal onset zones as verified by invasive intracranial electrodes or video-EEG monitoring. The case histories, interictal EEG, ictal semiology, other MRI findings in addition to hippocampal atrophy, and results of ictal SPECT and PET scans were evaluated. Results were compared with those of surgically proven medial temporal lobe epilepsy with hippocampal atrophy recruited during the same period. 8.5% of the intractable epilepsy patients with hippocampal atrophy had extra-medial temporal epileptogenic zones. A history of encephalitis and hemiconvulsion-hemiparesis were significantly common in the EMTE group. Most of the interictal EEGs of EMTE patients showed extratemporal irritative zones. MRI, ictal SPECT, and FDG-PET seemed to be helpful at localizing the true epileptogenic zones. The predominant EMTE seizure type was focal motor seizure with secondary generalization. Some portion of intractable epilepsy patients with hippocampal atrophy had extra-medial-temporal epileptogenic foci and careful analysis of semiology and neuroimagings could yield clues to correct diagnosis.

Adult↗
PubMed2000

Ion chromatography detector based on solid-state ion-selective electrode array.

A variety of neutral carrier type ionophores for monovalent cations were employed to prepare solid-state cation-selective electrodes (SSEs) for use as a detector in single-column ion chromatography (IC). The polyurethane-based pseudoreference electrode made it possible to assemble an array type SSE detector for IC. An SSE-based detector provides not only the overall chromatogram for the separated ion species (monensin methyl ester-nonactin-based membrane), but also the enhanced chromatogram for specified ions of interest (valinomycin as K+ and nonactin for NH4+). This feature makes it possible to perform highly quantitative analysis with low detection limits even if the separation efficiency of the ion-exchange is not sufficient. Since SSE-based IC detectors are easily miniaturized and replaceable at low cost, they are an ideal component of a portable IC system.

Cations, Monovalent↗
PubMed2000

Visual working memory revealed by repetitive transcranial magnetic stimulation.

We evaluated whether repetitive transcranial magnetic stimulation (rTMS) could be utilized for studying the hemispheric lateralization and anatomical localization of the cortical areas of the visual system that are concerned with object-related visual working memory. In eight normal volunteers, visual working memory was tested during rTMS delivery over nine regions in each hemisphere. Visual working memory was significantly disturbed by rTMS over the right hemisphere compared with the left (P<0.05). The disturbance in visual working memory by rTMS was significant over the right inferior frontal (F8), inferior temporal (T8), and middle parietal (P4) areas compared with the control region (P<0.05). This study suggests that visual working memory is lateralized to the right hemisphere and localized in the right inferior frontal, inferior temporal, and middle-parietal areas. As a non-invasive tool, rTMS may be useful for the functional localization of the working memory system.

Adult↗
PubMed2000

Thiazole-containing benzo-crown ethers: a new class of ammonium-selective ionophores

A new class of crown ethers containing heterocyclic units has been designed to develop synthetic NH4+-selective ionophores whose resulting potentiometric properties in solvent polymeric membranes are superior or at least comparable to those of nonactin. It was found that the derivatives of thiazole containing dibenzo-18-crown-6 (1; TDB18C6) incorporated in PVC-based membranes provide enhanced NH4+ selectivities over alkali metal cations, especially over Na+, compared to those of the nonactin-doped membranes: for example, the selectivity coefficients, log K(POT)NH4+J (J = Li+, Na+, K+), for the 2-nitrophenyloctyl ether (NPOE) plasticized PVC membranes doped with the hexyl chain-substituted TDB18C6 (2) were -4.9, -3.9, and -1.3, while those for the same type of membranes with nonactin -4.4, -3.0, and -1.0, respectively. Unlike other synthetic NH4+-selective neutral carriers reported to date, TDB18C6-type compounds result in potentiometric performance highly comparable to that of the nonactin-based ones except their slightly higher detection limits (approximately 3 x 10(-6) vs 7 x 10(-7)). The complex formation between TDB18C6 and NH4+ was identified from 1H NMR spectra. The 1:1 complex formation constant of TDB18C6 with NH4+ in solvent polymeric membranes estimated using the method suggested by Bakker et al. and the NH4+ selectivity coefficient over K+ (K(POT)NH4+,K+) are approximately 200 times smaller than that of nonactin (1.8 x 10(7) vs 3.6 x 10(9)).

Journal Article↗
PubMed2000

Potentiometric evaluation of solvent polymeric carbonate-selective membranes based on molecular tweezer-type neutral carriers

Potentiometric properties of the ion-selective electrodes) based on highly plasticized PVC membranes doped with the carbonate-selective cholic acid (CA) derivatives have been measured. The carbonate-selective neutral carriers have been prepared by coupling one to three trifluoroacetobenzoyl (TFAB) groups to a cholic acid derivative which has three hydroxyl linkers lining on the C3, C7, and C12 positions of its rigid steroidal ring structure. The membranes based on cholic acid derivatives with two TFABs [3,7-bis(TFAB)CA, 3,12-bis(TFAB)CA, and 7,12-bis(T-FAB)CA] exhibited remarkably improved carbonate selectivity, indicating that the bis(FAB)CAs behave like molecular tweezers for the carbonate ion. For example, 3,12-bis(TFAB)CA resulted in 10-300-fold-enhanced carbonate selectivity over other anions (e.g., salicylate, ClO4-, SCN-, (HPO4)2-, NO3-, NO2-, Br-, and Cl-) compared to that of the neutral carriers with a single TFAB group. The distances between the carbonate binding centers of bis(TFAB)CAs, i.e., the carbonyl carbons of the two TFAB groups, are in the 7.3-7.9-A range at the AM1 level semiempirical calculation, which is too far for the carbonate ion to form direct covalent bonding. The fast atom bombardment mass spectra of bis(TFAB)CAs show that significant fractions of the compounds are either mono- or dihydrated before complexing the carbonate ion. These findings seem to suggest that bis(TFAB)CAs recognize the incoming carbonate ion by forming both covalent and hydrogen bonding between the hydrated and unhydrated TFAB groups. The analytical utility of the carbonate-selective electrode based on 3,12-bis(TFAB)-CA has been demonstrated by measuring the total carbon dioxide in human serum in the presence of lipophilic anion interferents, e.g., salicylate.

Journal Article↗
PubMed2000

A planar pCO2 sensor with enhanced electrochemical properties.

To develop planar microchemical pCO2 sensing devices with improved electrochemical properties, we combined two advanced technologies. One is a differential sensor arrangement to simplify the microfabrication procedure by employing pH-sensitive gas-permeable membranes, and the other is the use of an enzyme (carbonic anhydrase) to shorten total measurement time by accelerating the rate of CO2 hydration. The adhesion of the polyurethane-matrix gas-permeable membrane is enhanced significantly by incorporating a silanizing reagent (silicon tetrachloride), improving the stability and extending sensor lifetime. The proposed differential pCO2 microelectrodes exhibited significantly improved performance in their preconditioning period, response and recovery times, stability, response slope, and lifetime.

Biosensing Techniques↗
PubMed2000

A disposable amperometric sensor screen printed on a nitrocellulose strip: a glucose biosensor employing lead oxide as an interference-removing agent.

A new type of disposable amperometric sensor is devised by screen printing thick-film electrodes directly on a porous nitrocellulose (NC) strip. The chromatographic NC strip is then utilized to introduce various sample pretreatment layers. As a preliminary application, a glucose biosensor based on hydrogen peroxide detection is constructed by immobilizing glucose oxidase (GOx) on the NC electrode strip and by formulating a strong oxidation layer (i.e., PbO2) at the sample loading area, placed below the GOx reaction band. The screen-printed PbO2 paste serves as a sample pretreatment layer that removes interference by its strong oxidizing ability. Samples applied are carried chromatographically, via the PbO2 paste, to the GOx layer, and glucose is catalyzed to liberate hydrogen peroxide, which is then detected at the electrode surface. The proposed NC/PbO2 strip sensor is shown to be virtually insusceptible to interfering species such as acetaminophen and ascorbic and uric acids and to exhibit good performance, in terms of the sensor-to-sensor reproducibility (standard deviation, +/-0.026 - +/-0.086 microA), the sensitivity (slope, -0.183 microA/mM), and the linearity (correlation coefficient, 0.994 in the range of 0-10 mM).

Biosensing Techniques↗
PubMed1998

Microtiter plate-format optode.

Microtiter plate-format optodes could be assembled by casting bulk-response membranes into the standard 96-well polypropylene-based plate or by screen printing them on an optically transparent substrate with 96-well pattern. The compositions of thick optode membranes, especially the ratios of poly(vinyl chloride) (PVC) to plasticizer [bis-(2-ethylhexyl) sebacate (DOS)], were carefully optimized to provide reproducible and rapid response. Adjusting the ratio of PVC to DOS by 1:6, bulk-response membranes containing neutral carrier (4-tert-butyl calix[4]arene tetraacetic acid tetraethyl ester for sodium-selective membrane or valinomycin for potassium-selective membrane) and lipophilic pH indicator (ETH 5294) could exhibit equilibrium response in 5 min. The practical utility of microtiter plate-format optodes has been examined by determining clinically relevant electrolytes in serum samples. It was demonstrated that microtiter plate-format optodes can provide high sample throughput (approximately 100 samples in less than 5 min), analytical performance comparable to that of a potentiometric clinical analyzer, and additional information on electrolytes using the same samples prepared for other colorimetric measurements.

Animals↗
PubMed1998

Results of thoracoscopic sympathectomy for 96 cases of palmar hyperhidrosis.

From August 1996 to August 1997, we performed thoracoscopic sympathectomy for 96 cases of palmer hyperhidrosis. The patients' ages were from 22 to 58 years old (mean age: 28; gender ratio: male/female: 3/2). Most of them were students, workers or clerks. The patients were divided in two series: in 61 patients, the sympathetic chain before the 2nd to 4th ribs was removed in the lateral approach with a 3 hole procedure. In 35 patients, the 2nd portion of the sympathetic chain was destroyed (by electric cauter) in the posterior approach with a 2 hole procedure. The results were almost the same in the first series (all cases have a fair benefit), but in the second series, some advantages may be useful for therapy, i.e no need to turn the patients, severe compensation sweating is minimized (from 4% ==> 0%) and the amount of holes is reduced.

Adrenergic Fibers↗