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Chung SH, Hoyles M, Allen T, Kuyucak S. Study of ionic currents across a model membrane channel using Brownian dynamics. Biophys J 1998; 75:793-809. [PMID: 9675181 PMCID: PMC1299754 DOI: 10.1016/s0006-3495(98)77569-1] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Brownian dynamics simulations have been carried out to study ionic currents flowing across a model membrane channel under various conditions. The model channel we use has a cylindrical transmembrane segment that is joined to a catenary vestibule at each side. Two cylindrical reservoirs connected to the channel contain a fixed number of sodium and chloride ions. Under a driving force of 100 mV, the channel is virtually impermeable to sodium ions, owing to the repulsive dielectric force presented to ions by the vestibular wall. When two rings of dipoles, with their negative poles facing the pore lumen, are placed just above and below the constricted channel segment, sodium ions cross the channel. The conductance increases with increasing dipole strength and reaches its maximum rapidly; a further increase in dipole strength does not increase the channel conductance further. When only those ions that acquire a kinetic energy large enough to surmount a barrier are allowed to enter the narrow transmembrane segment, the channel conductance decreases monotonically with the barrier height. This barrier represents those interactions between an ion, water molecules, and the protein wall in the transmembrane segment that are not treated explicitly in the simulation. The conductance obtained from simulations closely matches that obtained from ACh channels when a step potential barrier of 2-3 kTr is placed at the channel neck. The current-voltage relationship obtained with symmetrical solutions is ohmic in the absence of a barrier. The current-voltage curve becomes nonlinear when the 3 kTr barrier is in place. With asymmetrical solutions, the relationship approximates the Goldman equation, with the reversal potential close to that predicted by the Nernst equation. The conductance first increases linearly with concentration and then begins to rise at a slower rate with higher ionic concentration. We discuss the implications of these findings for the transport of ions across the membrane and the structure of ion channels.
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Chung SH, Song WJ, Kim K, Bednarski JJ, Chen J, Prestwich GD, Holz RW. The C2 domains of Rabphilin3A specifically bind phosphatidylinositol 4,5-bisphosphate containing vesicles in a Ca2+-dependent manner. In vitro characteristics and possible significance. J Biol Chem 1998; 273:10240-8. [PMID: 9553075 DOI: 10.1074/jbc.273.17.10240] [Citation(s) in RCA: 100] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the present study we investigated the lipid binding characteristics of the C2 domains of Rabphilin3a. We found that the tandem C2 domain of Rabphilin3a specifically bound lipid vesicles containing phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) in a Ca2+-dependent manner. There was little binding to vesicles containing PtdIns(3,4)P2 in the presence or absence of Ca2+. Binding to phosphatidylinositol 3,4,5-triphosphate-containing vesicles was similar to binding to PtdIns(4,5)P2-containing vesicles. The presence of physiological amounts of phosphatidylserine (PS) greatly potentiated the ability of PtdIns(4,5)P2 to cause vesicle binding. As with the C2 domains together, the binding of individual C2 domain of Rabphilin3a was much greater to PtdIns(4,5)P2-containing vesicles than PtdIns(3,4)P2-containing vesicles. Both C2 domains also bound 29 mol % PS-containing vesicles in a Ca2+-dependent manner. Because of the importance of the C2B domain in the enhancement of secretion from chromaffin cells by Rabphilin3a, its biochemistry was further investigated. The mutation of aspartates 657 and 659 to asparagines in C2B decreased Ca2+-dependent and increased Ca2+-independent vesicle binding, indicating the Ca2+ dependence of the domain is provided by aspartic acid residues in the putative Ca2+-binding pocket. A peptide from the COOH-terminal region of the C2B domain specifically inhibited ATP-dependent secretion from permeabilized chromaffin cells and the binding of Rabphilin3a to phosphatidylcholine/PS/PtdIns(4,5)P2-containing lipid vesicles, suggesting a role of this sequence in secretion through its ability to interact with acidic lipid vesicles.
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Kim JH, Shin T, Chung JD, Kwon OY, Choi NC, Chung SH, Lim BH. Temporal pattern of blood volume change in cerebral infarction: evaluation with dynamic contrast-enhanced T2*-weighted MR imaging. AJR Am J Roentgenol 1998; 170:765-70. [PMID: 9490971 DOI: 10.2214/ajr.170.3.9490971] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
OBJECTIVE The purposes of this study were to evaluate the temporal pattern of blood volume change in cerebral infarction and to provide a guideline in the interpretation of blood volume data, which are known to vary according to the stage of infarction. SUBJECTS AND METHODS Thirty-three patients with large middle cerebral infarctions were examined one to three times (one time in 20 patients, two times in eight patients, and three times in five patients) after the onset of stroke by dynamic contrast-enhanced T2*-weighted MR imaging and MR angiography. A total of 54 infarctions (29 in an acute stage [up to 7 days], 15 in a subacute stage [8-21 days], and 10 in a chronic stage [22-35 days]) were included. After blood volume maps were created, blood volume ratios (blood volume of the infarcted region divided by blood volume of corresponding contralateral region) were compared at different stages. Likewise, findings on MR angiography were compared at different stages. RESULTS Mean blood volume ratios in each stage of infarction were 0.46 in the acute stage, 1.48 in the subacute stage, and 0.73 in the chronic stage (p < .001). Recanalization of occluded arteries occurred in 21% of infarctions in the acute stage and 80% in the subacute stage. Infarctions with recanalization had higher blood volume ratios than did those without recanalization (p < .001). A biphasic pattern of blood volume ratios was found in 13 patients who underwent at least two MR examinations: increased blood volume in the subacute stage and decreased blood volume in the chronic stage, regardless of recanalization (p < .01). CONCLUSION Blood volume that initially decreases in cerebral infarction increases in the subacute stage, reflecting reperfusion hyperemia. Blood volume decreases again in the chronic stage. The time interval between onset of stroke and MR examination must be considered for correct interpretation of blood volume data in cerebral infarction at various stages.
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Yanagawa H, Chung SH, Ogawa Y, Sato K, Shibata-Seki T, Masai J, Ishiguro K. Protein anatomy: C-tail region of human tau protein as a crucial structural element in Alzheimer's paired helical filament formation in vitro. Biochemistry 1998; 37:1979-88. [PMID: 9485325 DOI: 10.1021/bi9724265] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Tau is a microtubule-associated protein in mammalian brain. In Alzheimer's disease, this protein is present in the somatodendritic compartment of certain nerve cells, where it forms a portion of paired helical filament, the major constituent of the neurofibrillary tangle. For clarification of the mechanism of this formation, recombinant human tau and its fragments (N-terminal half, C-terminal half, and 4-repeats) expressed in Escherichia coli were prepared, eight peptide fragments (C-tails 1-8) of the C-tail region were synthesized, and the conformation and capacity for aggregation essential for filamentous structure formation in vitro were examined. Recombinant full-length tau, the N-terminal half, 4-repeats, and the C-terminal half did not form filamentous structures in aqueous solution after standing at 20 degrees C. Peptides corresponding to the C-tail region of tau, C-tail 5, C-tail 7, and C-tail 8, produced the paired filament or single straight filament in acidic solution. The rate of filament formation by each peptide was followed by circular dichroism, which showed the C-tails to have predominantly random coil structures immediately following dissolution in aqueous solution and be gradually converted to the beta-sheet structure. The kinetics of aggregation were characterized by a delay period during which the solution remained clear, followed by a nucleation event which led to a growth phase, whose negative peak intensity at 218 nm in circular dichroism increased due to filamentous structure formation. This delay was eliminated by seeding supersaturated solution of preformed filaments. C-tails interacted with recombinant full-length tau to form definite single straight filament. The C-tail region of tau is thus shown indispensable to the formation of paired helical filament and nucleation to reduce the rate of paired helical filament formation in amyloidogenesis in vitro. These findings may provide some clarification of the pathogenesis of Alzheimer's disease.
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Kuyucak S, Hoyles M, Chung SH. Analytical solutions of Poisson's equation for realistic geometrical shapes of membrane ion channels. Biophys J 1998; 74:22-36. [PMID: 9449306 PMCID: PMC1299358 DOI: 10.1016/s0006-3495(98)77763-x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Analytical solutions of Poisson's equations satisfying the Dirichlet boundary conditions for a toroidal dielectric boundary are presented. The electric potential computed anywhere in the toroidal conduit by the analytical method agrees with the value derived from an iterative numerical method. We show that three different channel geometries, namely, bicone, catenary, and toroid, give similar potential profiles as an ion traverses along their central axis. We then examine the effects of dipoles in the toroidal channel wall on the potential profile of ions passing through the channel. The presence of dipoles eliminates the barrier for one polarity of ion, while raising the barrier for ions of the opposite polarity. We also examine how a uniform electric field from an external source is affected by the protein boundary and a mobile charge. The channel distorts the field, reducing it in the vestibules, and enhancing it in the constricted segment. The presence of an ion in one vestibule effectively excludes ions of the same polarity from that vestibule, but has little effect in the other vestibule. Finally, we discuss how the solutions we provide here may be utilized to simulate a system containing a channel and many interacting ions.
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Li SC, Hoyles M, Kuyucak S, Chung SH. Brownian dynamics study of ion transport in the vestibule of membrane channels. Biophys J 1998; 74:37-47. [PMID: 9449307 PMCID: PMC1299359 DOI: 10.1016/s0006-3495(98)77764-1] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Brownian dynamics simulations have been carried out to study the transport of ions in a vestibular geometry, which offers a more realistic shape for membrane channels than cylindrical tubes. Specifically, we consider a torus-shaped channel, for which the analytical solution of Poisson's equation is possible. The system is composed of the toroidal channel, with length and radius of the constricted region of 80 A and 4 A, respectively, and two reservoirs containing 50 sodium ions and 50 chloride ions. The positions of each of these ions executing Brownian motion under the influence of a stochastic force and a systematic electric force are determined at discrete time steps of 50 fs for up to 2.5 ns. All of the systematic forces acting on an ion due to the other ions, an external electric field, fixed charges in the channel protein, and the image charges induced at the water-protein boundary are explicitly included in the calculations. We find that the repulsive dielectric force arising from the induced surface charges plays a dominant role in channel dynamics. It expels an ion from the vestibule when it is deliberately put in it. Even in the presence of an applied electric potential of 100 mV, an ion cannot overcome this repulsive force and permeate the channel. Only when dipoles of a favorable orientation are placed along the sides of the transmembrane segment can an ion traverse the channel under the influence of a membrane potential. When the strength of the dipoles is further increased, an ion becomes detained in a potential well, and the driving force provided by the applied field is not sufficient to drive the ion out of the well. The trajectory of an ion navigating across the channel mostly remains close to the central axis of the pore lumen. Finally, we discuss the implications of these findings for the transport of ions across the membrane.
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Chung SH, Swindle J. Trypanosoma cruzi: circularization of linear DNA fragments prior to integration during generation of stable transformants. Mol Biochem Parasitol 1997; 89:321-5. [PMID: 9364977 DOI: 10.1016/s0166-6851(97)00127-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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83
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Chung SH, Stabila P, Macara IG, Holz RW. Importance of the Rab3a-GTP binding domain for the intracellular stability and function of Rabphilin3a in secretion. J Neurochem 1997; 69:164-73. [PMID: 9202307 DOI: 10.1046/j.1471-4159.1997.69010164.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We had previously demonstrated that Rab3a-GTP inhibits and the Rab3a-binding protein Rabphilin3a enhances secretion in bovine chromaffin cells. In this study, we investigated the role of Rab3a-GTP binding in the intracellular expression and the function of Rabphilin3a in regulated exocytosis in bovine chromaffin cells. Using transient transfections, we found that a minimal domain, Rp(51-190), that inhibits secretion coincides with a minimal domain that effectively binds Rab3a-GTP and allows intracellular stability of the construct. This domain includes a cysteine-rich, Zn2+-binding domain whose integrity is also required for Rab3a-GTP binding and the ability to inhibit secretion. A Rabphilin3a mutant, containing both C2 domains but defective in Rab3a-GTP, and wild-type Rabphilin3a both localized to chromaffin granules and stimulated secretion similarly despite lessened intracellular expression of the mutant protein. The data are consistent with a sequence of events in which a Rab3a-GTP x Rabphilin3a complex forms on the secretory granule as a precursor in a pathway that enhances secretion. The complex dissociates (perhaps because of GTP hydrolysis) to permit the enhancement of secretion by Rabphilin3a.
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Kim HJ, Park ED, Kim JH, Hwang EG, Chung SH. Odontogenic versus nonodontogenic deep neck space infections: CT manifestations. J Comput Assist Tomogr 1997; 21:202-8. [PMID: 9071285 DOI: 10.1097/00004728-199703000-00006] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
PURPOSE The purpose of this study was to evaluate deep neck space infection (DNSI) with particular attention to the differences in the spaces involved and in complications between odontogenic and nonodontogenic groups with CT. METHOD Forty-four patients (21 odontogenic and 23 nonodontogenic) were included in this study. Among odontogenic DNSI cases, 15 had dental infection in the second or third mandibular molar. We compared the CT features between odontogenic and nonodontogenic DNSI cases, with special emphasis on the differences in the spaces involved and in the rate and type of complications. RESULTS In all patients, CT clearly differentiated abscess from cellulitis. The most common spaces involved in 21 patients with odontogenic DNSI were the parapharyngeal (n = 18), the submandibular (n = 18), the anterior visceral (n = 13), the masticator (n = 9), and the sublingual (n = 7) spaces. In contrast, in 23 patients with nonodontogenic DNSI, the anterior visceral space (n = 14) was most frequently involved. The parapharyngeal, submandibular, and masticator spaces were statistically more frequently involved in odontogenic than in nonodontogenic DNSI (p < 0.05). Twenty-two patients had one or more complications shown by CT, of which airway compromise was more frequent and severe in odontogenic than in nonodontogenic DNSI. CONCLUSION We conclude that the parapharyngeal, submandibular, and masticator spaces are more significantly vulnerable in odontogenic DNSI than in nonodontogenic DNSI. The predilection for certain spaces of the neck in odontogenic DNSI seems to originate from the intimate relationship of the mandibular molars to the adjacent deep neck spaces.
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Song WJ, Chung SH, Kurnit DM. The murine Dyrk protein maps to chromosome 16, localizes to the nucleus, and can form multimers. Biochem Biophys Res Commun 1997; 231:640-4. [PMID: 9070862 DOI: 10.1006/bbrc.1997.6154] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We mapped the murine copy of the Dyrk gene and examined its subcellular localization and self-interaction. We found that: (1) Dyrk maps to the distal portion of MMU chromosome 16, consistent with previous mapping of the human DYRK gene to the Down syndrome critical region on HSA 21q22.2. (2) The Dyrk protein localizes to the cell nucleus, affording the potential of controlling the expression of other gene(s). (3) The Dyrk protein can self-associate in a two-hybrid system, in accord with the presence of a leucine zipper motif noted in the original sequence. In particular, its expression pattern in frontal brain nuclei during murine embryogenesis, its subcellular localization and its ability to interact with other proteins all suggest that this protein remains a good candidate to mediate some of the pleiotropic effects of Down syndrome.
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Chung SH, Kim MJ, Lee JY, Chung JH. Effects of probenecid on platelet aggregation and cytotoxicity: drawbacks of the use of probenecid in monitoring intracellular calcium metabolism. Thromb Res 1997; 85:345-50. [PMID: 9062958 DOI: 10.1016/s0049-3848(97)00020-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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Chung JH, Seo DC, Chung SH, Lee JY, Seung SA. Metabolism and cytotoxicity of menadione and its metabolite in rat platelets. Toxicol Appl Pharmacol 1997; 142:378-85. [PMID: 9070361 DOI: 10.1006/taap.1996.8048] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Previous studies suggest that menadione is cytotoxic to rat platelets by oxidative stress. In order to elucidate the mechanism of this toxicity, metabolism of menadione and the cytotoxicity of a metabolite, menadione-glutathione conjugate (MEN-SG), were investigated in platelet rich plasma and washed platelet (WP) systems. When menadione was incubated in platelets, the primary metabolite was MEN-SG, which was excreted into the incubation medium. Incubation of subcellular fractions of platelets with synthetic MEN-SG led to increases in oxygen consumption that were similar to the parent compound, menadione. However, unlike menadione, exposure of MEN-SG to intact platelets in WP system neither resulted in increased oxygen consumption nor induced cell lysis as measured by lactate dehydrogenase leakage. In contrast to menadione, levels of MEN-SG in the incubation medium were unaffected by the presence of platelets, suggesting that MEN-SG was not consumed (or taken up) by platelets. These results indicate that even though MEN-SG was able to induce oxidative stress within platelets as potently as menadione itself, the MEN-SG formation from menadione in platelets appeared not to contribute to menadione's cytotoxicity. This lack of MEN-SG toxicity was likely due to its rapid excretion outside the cells.
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Brown DM, Chung SH, Lantieri LA, Sampath TK, Hodge JC, Kania NM, Vannier MW, Khouri RK. Osteochondral allografts with an intramedullary muscle flap in rabbits. Clin Orthop Relat Res 1997:282-90. [PMID: 9005925] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
A model for hemijoint reconstruction using partially demineralized and lyophilized osteochondral allografts combined with an intramedullary muscle flap is described. The proximal 2/3 of the humerus was resected in 10 rabbits. The remaining defect was reconstructed with either a control lyophilized osteochondral allograft or a lyophilized allograft with a muscle flap filling the marrow cavity. Graft healing was followed by serial radiographs and magnetic resonance imaging. The grafts were harvested at 5 weeks for histologic analysis. By 5 weeks, 4 of 5 control allografts had fractured. In contrast, only 1 allograft with an intramedullary muscle flap showed evidence of a cortical break. Magnetic resonance imaging of control allografts showed a persistent large dead space within the marrow cavity and callus formation only at the outer cortical surface. Magnetic resonance imaging of allografts with an intramedullary muscle flap showed muscle obliterating the marrow cavity and areas of callus formation at both the outer and inner cortical surfaces. Histologically, graft incorporation was occurring at the outer cortical surface of the control allografts. In contrast, graft incorporation was occurring at both the outer and inner cortical surfaces of the allografts with an intramedullary muscle flap. The articular surface of the control allografts was severely degenerated. In allografts with an intramedullary muscle flap, the articular surface was smoother. Joints reconstructed with allografts with an intramedullary muscle flap had a significantly better range of motion at 5 weeks compared with control allografts. These results suggest that an intramedullary muscle flap can improve the functional results of joints reconstructed with partially demineralized and lyophilized osteochondral allografts by providing both vascularity and an increased population of mesenchymal stem cells capable of responding to bone morphogenetic proteins that reside in the partially demineralized allograft.
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Song WJ, Sternberg LR, Kasten-Sportès C, Keuren ML, Chung SH, Slack AC, Miller DE, Glover TW, Chiang PW, Lou L, Kurnit DM. Isolation of human and murine homologues of the Drosophila minibrain gene: human homologue maps to 21q22.2 in the Down syndrome "critical region". Genomics 1996; 38:331-9. [PMID: 8975710 DOI: 10.1006/geno.1996.0636] [Citation(s) in RCA: 134] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The presence of an extra copy of human chromosome 21 (trisomy 21), especially region 21q22.2, causes many phenotypes in Down syndrome, including mental retardation. To study genes potentially responsible for some of these phenotypes, we cloned a human candidate gene (DYRK) from 21q22.2 and its murine counterpart (Dyrk) that are homologous to the Drosophila minibrain (mnb) gene required for neurogenesis and to the rat Dyrk gene (dual specificity tyrosine phosphorylation regulated kinase). The three mammalian genes are highly conserved, >99% identical at the protein level over their 763-amino-acid (aa) open reading frame; in addition, the mammalian genes are 83% identical over 414 aa to the smaller 542-aa mnb protein. The predicted human DYRK and murine Dyrk proteins both contain a nuclear targeting signal sequence, a protein kinase domain, a putative leucine zipper motif, and a highly conserved 13-consecutive-histidine repeat. Fluorescence in situ hybridization and regional mapping data localize DYRK between markers D21S336 and D21S337 in the 21q22.2 region. Northern blot analysis indicated that both human and murine genes encode approximately 6-kb transcripts. PCR screening of cDNA libraries derived from various human and murine tissues indicated that DYRK and Dyrk are expressed both during development and in the adult. In situ hybridization of Dyrk to mouse embryos (13, 15, and 17 days postcoitus) indicates a differential spatial and temporal pattern of expression, with the most abundant signal localized in brain gray matter, spinal cord, and retina. The observed expression pattern is coincident with many of the clinical findings in trisomy 21. Its chromosomal locus (21q22. 2), its homology to the mnb gene, and the in situ hybridization expression patterns of the murine Dyrk combined with the fact that transgenic mice for a YAC to which DYRK maps are mentally deficient suggest that DYRK may be involved in the abnormal neurogenesis found in Down syndrome.
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Kim JH, Shin T, Kim JS, Kim HJ, Chung SH. MR imaging of cerebral activation performed with a gradient-echo technique at 1.5 T: sources of activation signals. AJR Am J Roentgenol 1996; 167:1277-81. [PMID: 8911195 DOI: 10.2214/ajr.167.5.8911195] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
OBJECTIVE MR imaging of cerebral activation has been successfully performed at 1.5 T for functional maps of the brain. However, major sources of activation signals in such imaging remain controversial. The purpose of this study is to investigate anatomic and physiologic sources of activation signals in MR imaging of cerebral activation performed with a gradient-echo technique at 1.5 T. SUBJECTS AND METHODS Motor cortex activation studies (n = 8) were conducted using a gradient-echo technique (80/60 [TR/TE], 40 degrees flip angle). MR venograms were then obtained at the same imaging plane to visualize the cortical veins, which were then compared with the shape and location of the activation signals. To investigate the physiologic sources of activation signal, the activation studies were repeated with different TEs (15, 30, and 60 msec), which allowed us to evaluate the blood oxygen level-dependent effect; with different flip angles (40 degrees and 10 degrees); and without and with presaturation of adjacent sections, all of which allowed us to evaluate inflow effect. RESULTS All activation signals were detected in the sulcus just posterior (n = 7) or lateral (n = 1) to the motor cortex. In seven of eight studies, shape and location of these signals corresponded well with those of the cortical veins. In the eighth study, the correspondence was partial. Activation signals significantly increased at a TE of 60 msec (p < .01), suggesting enhancement of the blood oxygen level-dependent effect at a long TE. Activation signals significantly decreased with a 10 degrees flip angle (p < .01) and with presaturation of adjacent sections (p < .01), indicating that the inflow effect was suppressed by a small flip angle and the elimination of unsaturated inflowing protons. CONCLUSION Our results suggest that signals in cerebral activation obtained by MR imaging with a gradient-echo technique at 1.5 T arise mainly from the cortical veins draining the activated cortex. Physiologically, both blood oxygen level-dependent and inflow effects contribute to signal generation.
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Chung SH, Kennedy RA. Coupled Markov chain model: characterization of membrane channel currents with multiple conductance sublevels as partially coupled elementary pores. Math Biosci 1996; 133:111-37. [PMID: 8718705 DOI: 10.1016/0025-5564(95)00084-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
A parameterized Markov chain model is developed to represent the characteristics of channel currents that either are the superposition of many single channels or show multiple conductance sublevels. The simplified model takes the form of a set of binary chains that are interdependent according to a simple lumped coupling parameter. When varied, this parameter realizes a range of behaviors from tight coupling to complete independence. Other model parameters describe the intrinsic characteristics of the binary chains. An identification procedure for the model parameters is developed based on hidden Markov modeling ideas but incorporating a novel parameter estimation. The usefulness of the model in analyzing certain types of data is demonstrated with examples of real channel currents.
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Hoyles M, Kuyucak S, Chung SH. Energy barrier presented to ions by the vestibule of the biological membrane channel. Biophys J 1996; 70:1628-42. [PMID: 8785322 PMCID: PMC1225132 DOI: 10.1016/s0006-3495(96)79726-6] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The role of the vestibule in influencing the permeation of ions through biological ion channels is investigated. We derive analytical expressions for the electric potential satisfying Poisson's equation with prolate spheroidal boundary conditions. To allow more realistic geometries we devise an iterative method to calculate the electric potential arising from a fixed charge and an arbitrary dielectric boundary, and confirm that the analytical expressions and iterative method give similar potential values. We then investigate the size of the potential barrier presented to an ion by model vestibules of conical and catenary shapes. The height of the potential barrier increases steeply as an ion enters the vestibule and moves toward the constricted region of the channel. We show that the barrier presented by, for example, a 15 degrees conical vestibule can be canceled by placing dipoles with a total moment of about 50 Debyes near the constricted region of the pore. The selectivity of cations and anions can result from the polarity of charge groups or the orientation of dipoles located near the constricted region of the channel.
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Lantieri LA, Ozbek MR, Deune EG, Ornberg RL, Brown DM, Chung SH, Wun TC, Cooley BC, Khouri RK. Prevention of microvascular thrombosis by topical application of recombinant tissue factor pathway inhibitor. Plast Reconstr Surg 1996; 97:587-94. [PMID: 8596790 DOI: 10.1097/00006534-199603000-00015] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Tissue factor pathway inhibitor is a naturally occurring protein inhibitor of factor X and the tissue factor-factor VII complex of the extrinsic pathway of coagulation. The potential of tissue factor pathway inhibitor as a topical antithrombotic agent was evaluated in a rabbit model of thrombosis that combined intimal injury, anastomosis, and a twisted pedicle. In 207 rabbit ears, a near-complete amputation was performed, preserving the central ear artery and vein. The central ear artery was transected, the intima was removed mechanically over a 1-cm length, the artery was anastomosed, and the ear was twisted 360 degrees, wrapping the intact vein around the artery. Before recirculation, the lumen was irrigated on a blinded, randomized basis with either hirudin (100 or 500 units/ml), heparin (50 or 100 units/ml), tissue factor pathway inhibitor (10, 40, 125, or 250 microgram/ml), heparin and tissue factor pathway inhibitor together, or vehicle (control). Upon arterial reflow, the ears were observed for 7 days. Patency rates after 7 days were as follows: hirudin, 30 and 55 percent; heparin, 43 and 50 percent; tissue factor pathway inhibitor, 75 and 90 percent; heparin and tissue factor pathway inhibitor, 75 percent; and vehicle, 6 percent. The higher concentrations of tissue factor pathway inhibitor led to significantly higher patency rates than heparin, hirudin, or control solutions. Electron microscopic evaluation of specimens irrigated with gold- labeled tissue factor pathway inhibitor revealed the inhibitor bound to the injured intimal surface for at least 3 days postoperatively. Coagulation studies showed no change in the clotting profile upon intravascular infusion with tissue factor pathway inhibitor even at the highest dose used topically. We conclude that tissue factor pathway inhibitor is a more effective topical antithrombotic agent than either heparin or hirudin.
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Brown DM, Chung SH, Pasia EN, Khouri RK. Treatment of avascular ulcers with cytokine-induced tissue generation and skin grafting. Am J Surg 1996; 171:247-50. [PMID: 8619461 DOI: 10.1016/s0002-9610(97)89560-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
BACKGROUND Recombinant platelet-derived growth factor (rPDGF-BB) stimulates migration and proliferation of fibroblasts and smooth muscle cells and induces the rapid development of granulation tissue. This study investigated the use of rPDGF-BB and skin grafting to heal avascular ulcers using a rabbit model. We further investigated the effect of a hyaluronic acid carrier and a vascular pedicle on rPDGF-induced tissue generation in this model. METHODS Large avascular ulcers were created on both ears of New Zealand white rabbits. One ulcer was treated with topical rPDGF-BB, the other with control buffer. After 5 or 7 days, the amount of granulation tissue migration from the wound margin was measured, and the wounds were skin grafted. In another group of ulcers, rPDGF-BB treatment was combined with a hyaluronic acid disk or an intact central axial ear artery and vein. RESULTS Whereas control wounds generated 1.00 +/- 0.27 mm and 1.75 +/- 0.25 mm of granulated tissue migration from the wound margin by days 5 and 7, respectively, rPDGF-BB treatment increased the amount of granulation tissue migration to 1.88 +/- 0.23 mm and 3.00 +/- 0.86 mm by days 5 and 7 after treatment, respectively (P <0.05 at both time points). Hyaluronic acid disks stimulated 2.50 +/- 0.22 mm of granulation tissue migration by day 7 in controls; when rPDGF-BB was added to the carrier, the migration increased to 4.50 +/- 0.29 mm from the wound margin (P<0.05). Granulation tissue migration was further increased with an intact vascular pedicle: 5.75 +/- 0.48 mm in controls versus 7.75 +/- 0.25 mm with rPDGF-BB treatment (P<0.01). Skin grafts applied to the treated ulcers failed to survive in all groups except those with intact vascular pedicles. CONCLUSIONS. This study demonstrates that rPDGF-BB can increase the amount of granulation tissue generated over an avascular wound. This tissue generation is enhanced by both a hyaluronic acid carrier and a vascular pedicle. A vascular pedicle was required for skin graft survival. This study supports the role of hyaluronic acid in rPDGF-BB induced tissue generation and the requirement of a direct blood supply for functional cytokine-induced tissue generation.
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95
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Bahk JY, Hyun JS, Chung SH, Lee H, Kim MO, Lee BH, Choi WS. Stage specific identification of the expression of GnRH mRNA and localization of the GnRH receptor in mature rat and adult human testis. J Urol 1995; 154:1958-61. [PMID: 7563392] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
PURPOSE To identify the expression of gonadotropin-releasing hormone (GnRH) messenger ribonuclueic acid (mRNA) and localize GnRH receptors in mature rat and adult human testes. MATERIALS AND METHODS In situ hybridization and enzymatic receptor binding localization were performed. RESULTS GnRH mRNA was expressed within the seminiferous tubules in both mature rat and adult human testis. In rats, expression of GnRH mRNA was identified in the Sertoli cells and spermatogenic cells of some seminiferous tubules, but the other tubules did not express any hybridization signal. In humans, expression of GnRH mRNA was identified only in some spermatogenic cells in some seminiferous tubules. The receptors for GnRH were localized to cells in the interstitial tissues of the testis, probably Leydig cells. CONCLUSION The authors believe that the mature rat and adult human seminiferous tubular cells produce GnRH at the same specific stage of the spermatogenic cycle and that GnRH produced within seminiferous tubules, including Sertoli cells and spermatogenic cells, reacts with neighboring GnRH receptors in interstitial cells, including Leydig cells. The GnRH produced from the Sertoli cells in seminiferous tubules would react with GnRH receptors in interstitial cells as a paracrine hormone.
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96
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Chung SH, Takai Y, Holz RW. Evidence that the Rab3a-binding protein, rabphilin3a, enhances regulated secretion. Studies in adrenal chromaffin cells. J Biol Chem 1995; 270:16714-8. [PMID: 7622481 DOI: 10.1074/jbc.270.28.16714] [Citation(s) in RCA: 107] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Rabphilin3a had been identified in brain as a Rab3a-binding protein and may serve as an effector for Rab3a function. We have cloned a splice variant of brain-Rabphilin3a from a bovine adrenal chromaffin cell cDNA library and investigated the function of the protein in regulated exocytosis in bovine chromaffin cells. The predicted amino acid sequence of chromaffin cell (c-) Rabphilin3a was identical with that of brain (b-) Rabphilin3a except for a 6-amino-acid insert VFSLSA in the amino-terminal half of the protein. An antibody directed against a carboxyl-terminal peptide recognized an 85-kDa protein in COS7 cells transfected with the cDNA in a mammalian expression vector. A band of similar mobility was enriched in a fraction of highly purified chromaffin granule membranes, consistent with the Rabphilin3a being associated with chromaffin granule membranes. Overexpression of either chromaffin cell or brain Rabphilin3a by transfection with the corresponding cDNAs in mammalian expression vectors enhanced DMPP-induced secretion of co-expressed human growth hormone (GH) approximately 30%. Chromaffin cells transfected with a plasmid with the entire coding sequence of c-Rabphilin3a inserted in the antisense orientation inhibited secretion of co-expressed GH by approximately 30%. Rabphilin3a mutants lacking one or both of the carboxyl-terminal C2 domains strongly inhibited DMPP-stimulated exocytosis. The single C2 domain deletion also strongly inhibited Ca(2+)-dependent secretion from digitonin-permeabilized cells. These data indicate that Rabphilin3a is a positive regulator of exocytosis. Because the C2 deletion mutants contain the amino-terminal Rab3a-GTP binding domain, they may inhibit secretion by competing with endogenous Rabphilin3a for interaction with Rab3a-GTP without being able to mimic the functional effects of full-length Rabphilin3a.
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97
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Abstract
Single channel potassium currents activated indirectly via stimulation of metabotropic receptors were recorded in cell-attached patches on hippocampal neurones in slices from neonatal rats. When metabotropic receptors in the area outside of the patch are stimulated by glutamate, quisqualate and trans-ACPD, single channel currents appear with a predominant conductance level of about 20 pS. From the reversal potential and substitution of ionic species, we established that the currents are carried by potassium ions. Using selective blockers of ionotropic receptors in conjunction with specific agonists for the metabotropic receptor, it was ascertained that the channel observed is linked to metabotropic receptors. The currents display submaximal conductance states and fluctuate rapidly between evenly-spaced conductance sublevels.
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98
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Chung SH, Kuyucak S. Changes in the kinetics and conductance of N-methyl-D-aspartate (NMDA)-receptor activated single channels with temperature. Neurosci Lett 1995; 187:181-4. [PMID: 7542755 DOI: 10.1016/0304-3940(95)11369-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Single channel currents activated by N-methyl-D-aspartate (NMDA) were recorded in inside-out membrane patches from hippocampal pyramidal cells. The effects of temperature on the conductance level and the kinetics of single channels were accurately determined by using a digital signal processing technique based on hidden Markov models. With increasing temperature, the probability of the channel being in the open state increases steeply, as does the amplitude of channel currents. The proportional change in channel conductance with increasing temperature is greater than the corresponding change in bulk conductivity of 150 mM electrolyte solutions. From the temperature dependence of channel conductance and kinetics, we derived several thermodynamical properties of the NMDA-receptor activated channel. Among these are the height of the energy barrier V presented to an ion traversing the pore, the activation energy Ea and the enthalpy delta H of the channel.
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99
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Chung SH, Jeffrey KR, Stevens JR. 23Na NMR evidence for a change of diffusion mechanism in NaClO4-poly(propylene oxide). PHYSICAL REVIEW. B, CONDENSED MATTER 1995; 51:2826-2830. [PMID: 9979056 DOI: 10.1103/physrevb.51.2826] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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100
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Lee JD, Kim DS, Shin JS, Cho SN, Kim SJ, Shin DH, Chung SH, Lee JT, Park CY, Kim SM. Localization of intracellular monoclonal antibody specific for mycobacteria in experimentally induced pulmonary tuberculous lesion. Int Arch Allergy Immunol 1995; 106:113-7. [PMID: 7819738 DOI: 10.1159/000236830] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
To determine the intracellular localization of intravenously injected infection-specific monoclonal antibodies (mAbs) in the infected cells, immunohistochemical staining was carried out in an animal model having pulmonary tuberculous lesions induced by inoculation of heat-killed Mycobacterium tuberculosis H37Rv. One milligram of intact mouse mAb against mycobacteria (group I, n = 10) and F(ab')2 (group II, n = 6) was intravenously injected to the rabbits of each group. Immunohistochemical staining using an antimouse Ab was performed at days 1, 3, 5, 7 and 8 in group I and at days 1, 2 and 3 in group II by the streptavidin-biotin method. For the control study, 1 ml of nonspecific polyclonal human IgG (group III, n = 10) and 100 micrograms of normal rabbit IgG F(ab')2 (group IV, n = 6) was injected to rabbits and guinea pigs having tuberculous inflammation, respectively. Both groups (group I and II) showed a positive antigen (Ag)-Ab reaction within the cytoplasm of monocytes. A weak but positive reaction was observed intracellularly in group III; however, no positive reaction was seen in group IV. Our results suggest that an intracellular Ag-Ab reaction plays an important role in the localization of infection by immunoscintigraphy using specific mAb fragments.
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