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U Kim

Publications and source records attributed to U Kim.

At least 37 records · Page 2Linked to original sources
PubMed1999

A cluster of ABA-regulated genes on Arabidopsis thaliana BAC T07M07.

Arabidopsis thaliana BAC T07M07 encoding the abscisic acid-insensitive 4 (ABI4) locus has been sequenced completely. It contains a 95,713-bp insert and 24 predicted genes. Most putative genes were confirmed by gel-based RNA profiling and a cluster of ABA-regulated genes was identified. One of the 24 genes, designated PP2C5, encodes a putative protein phosphatase 2C. The encoded protein was expressed in Escherichia coli, and its enzyme activity in vitro was confirmed.

Abscisic Acid↗
PubMed1998

The functional influence of burst and tonic firing mode on synaptic interactions in the thalamus.

Thalamocortical and perigeniculate (PGN) neurons can generate action potentials either as Ca2+ spike-mediated high-frequency bursts or as tonic trains. Using dual intracellular recordings in vitro in monosynaptically connected pairs of PGN and dorsal lateral geniculate nucleus (LGNd) neurons, we found that the functional effect of synaptic transmission between these cell types was strongly influenced by the membrane potential and hence the firing mode of both the pre- and postsynaptic neurons. Activation of single action potentials or low-frequency spike trains in PGN or thalamocortical neurons resulted in the generation of PSPs that were 0.5-2.0 mV in amplitude. In contrast, the generation of Ca2+ spike-mediated bursts of action potentials in the presynaptic cell increased these PSPs to an average of 4.4 mV for the IPSP and 3.0 mV for the EPSP barrage, because of temporal summation and/or facilitation. If the postsynaptic neuron was at a resting membrane potential (e.g., -65 mV), these PSP barrages could result in the activation of a low-threshold Ca2+ spike and burst of action potentials. These results demonstrate that the burst firing mode of action potential generation is a particularly effective means by which perigeniculate and thalamocortical neurons may influence one another. We propose that the activation of burst discharges in these cell types is essential for the generation of some forms of synchronized rhythmic oscillations of sleep and of epileptic seizures.

Action Potentials↗
PubMed1998

Pneumatosis intestinalis and portal vein gas after blunt abdominal trauma.

The authors report on a 2-year-old boy in whom pneumatosis intestinalis (PI) and portal vein gas (PVG) resulted from blunt abdominal trauma after child abuse. The presumed pathophysiology of PI and PVG is mechanical in this setting. Its presence establishes mucosal injury but does not necessarily imply intestinal necrosis.

Abdominal Injuries↗
PubMed1998

Functional and ionic properties of a slow afterhyperpolarization in ferret perigeniculate neurons in vitro.

Intracellular recordings from spontaneously spindling GABAergic neurons of the ferret perigeniculate nucleus in vitro revealed a fast afterhyperpolarization after each action potential, a medium-duration afterhyperpolarization after each low-threshold Ca2+ spike, and a slow afterhyperpolarization after the cessation of spindle waves. The slow afterhyperpolarization was associated with an increase in membrane conductance, and the reversal potential was sensitive to extracellular [K+]o, indicating that it is mediated at least in part by the activation of a K+ conductance. However, the block of Ca2+ channels did not block the slow afterhyperpolarization, whereas the block of Na+ channels did block this event, even after the generation of repetitive Ca2+ spikes, indicating that it is mediated by a Na+-activated K+ current. Application of apamin reduced the afterhyperpolarization and enhanced a plateau potential after each low-threshold Ca2+ spike. This plateau potential could result in a prolonged depolarization of perigeniculate neurons, even before the application of apamin, resulting in the generation of tonic discharge. The plateau potential was blocked by the local application of tetrodotoxin, indicating that it is mediated by a persistent Na+ current. The activation and interaction of these slowly developing and persistent currents contributes significantly to low-frequency components of spindle wave generation. In particular, we suggest that the activation of the slow afterhyperpolarization may contribute to the generation of the spindle wave refractory period in vitro.

Action Potentials↗
PubMed1997

Functional dynamics of GABAergic inhibition in the thalamus.

The inhibitory gamma-aminobutyric acid-containing (GABAergic) neurons of the thalamic reticular and perigeniculate nuclei are involved in the generation of normal and abnormal synchronized activity in thalamocortical networks. An important factor controlling the generation of activity in this system is the amplitude and duration of inhibitory postsynaptic potentials (IPSPs) in thalamocortical cells, which depend on the pattern of activity generated in thalamic reticular and perigeniculate cells. Activation of single ferret perigeniculate neurons generated three distinct patterns of GABAergic IPSPs in thalamocortical neurons of the dorsal lateral geniculate nucleus: Low-frequency tonic discharge resulted in small-amplitude IPSPs mediated by GABAA receptors, burst firing resulted in large-amplitude GABAA IPSPs, and prolonged burst firing activated IPSPs mediated by GABAA and GABAB receptors. These functional properties of GABAergic inhibition can reconfigure the operations of thalamocortical networks into patterns of activity associated with waking, slow-wave sleep, and generalized seizures.

Action Potentials↗
PubMed1996

The B-cell-specific transcription coactivator OCA-B/OBF-1/Bob-1 is essential for normal production of immunoglobulin isotypes.

OCA-B was initially identified as a B-cell-restricted coactivator that functions with octamer binding transcription factors (Oct-1 and Oct-2) to mediate efficient cell type-specific transcription of immunoglobulin promoters in vitro. Subsequent cloning studies led to identification of the coactivator as a single polypeptide, designated either as OCA-B (ref. 3), OBF-1 (ref. 4) or Bob-1 (ref. 5). OCA-B itself does not bind to DNA directly, but interacts with either Oct-1 or Oct-2 to potentiate transcriptional activation. To determine the biological role of OCA-B, we generated OCA-B-deficient mice by gene targeting. Mice lacking OCA-B undergo normal antigen-independent, B-cell differentiation, including appropriate expression of both immunoglobulin genes and other early B-cell-restricted genes. However, antigen-dependent maturation of B cells is greatly affected. The proliferative response to surface IgM crosslinking is impaired, and there is a severe deficiency in the production of secondary immunoglobulin isotypes including IgG1, IgG2a, IgG2b, IgG3, IgA and IgE in OCA-B-deficient B cells. This defect is not due to a failure of the isotype switching process, but rather to reduced levels of transcription from normally switched immunoglobulin heavy-chain loci. In accord with the defective isotype production, germinal centre formation is absent in these mutant mice.

Animals↗
PubMed1996

Are the interlaminar zones of the ferret dorsal lateral geniculate nucleus actually part of the perigeniculate nucleus?

The ferret dorsal lateral geniculate nucleus (LGNd) contains interneurons within the interlaminar zones situated between the laminae corresponding to the ipsi- and contralateral eyes. We found that a subset of these neurons exhibits electrophysiological properties similar to those previously reported for perigeniculate (PGN) neurons, including the generation of rhythmic sequences of rebound low-threshold Ca2+ spikes at a frequency of 1-4 Hz after the intracellular injection of a hyperpolarizing current pulse. These "PGN-like" interlaminar interneurons innervated restricted regions of the A-laminae, inhibited thalamocortical cells through GABAA, and perhaps GABAB, receptors, and were excited by axon collaterals from thalamocortical cells. This reciprocal relationship is identical to that formed by PGN cells and allowed the PGN-like interlaminar neurons to participate in the generation of spindle waves and other network oscillations. Pharmacologically, PGN-like interlaminar interneurons were also similar to PGN neurons: both generated a prolonged depolarization in response to the local application of serotonin, 1S,3R-ACPD, and CCK8S, and a rapid depolarization followed by a more prolonged hyperpolarization in response to acetylcholine. Examination of parvalbumin and calbindin staining in the ferret LGNd revealed that both PGN and a subset of interlaminar neurons were parvalbumin-positive. In contrast, calbindin-positive cells were relatively absent in the PGN and sparsely present in the interlaminar zones, but were numerous in the A and C laminae. Our results indicate that the interlaminar zone in between laminae A and A1 and A1 and C in the ferret LGNd possesses a cell type that is electrophysiologically, pharmacologically, anatomically, immunocytochemically, and functionally similar to neurons in the PGN.

Animals↗
PubMed1996

Clinically occult carotid injury: a case for operative management.

A case is described of a clinically occult carotid artery lesion secondary to penetrating trauma. Angiography displayed a small intimal defect, whereas surgical exploration revealed significant intimal damage requiring excision and interposition grafting. This case supports the benefit of continued definitive operative management for carotid artery injuries.

Adolescent↗
PubMed1995

Pitfalls in the diagnosis of blunt diaphragmatic injury.

BACKGROUND: Severe blunt trauma to the torso can result in diaphragmatic disruption. Prompt recognition of this potentially life-threatening injury is difficult when the initial chest roentgenogram is unrevealing and immediate thoracotomy or celiotomy is not performed. This retrospective study was undertaken to: (1) determine the incidence of missed diaphragmatic injuries on initial evaluation; (2) identify factors contributing to diagnostic delays; and (3) formulate a diagnostic approach that reliably detects diaphragmatic rupture following blunt trauma. METHODS: Retrospective review of hospital records and radiographs from our 18-year experience with blunt diaphragmatic injuries. RESULTS: Seven of 57 (12%) blunt diaphragmatic injuries were missed on initial evaluation. Recognition followed 2 days to 3 months later. Two (4%) isolated left-sided injuries initially presented with normal chest roentgenograms. Five patients (9%) (4 with right-sided ruptures) had abnormalities on chest roentgenogram or computed tomography (CT) initially attributed to chest trauma. They were diagnosed by radionuclide, ultrasound, or CT investigations of hemothorax, pulmonary sepsis, and right upper quadrant pain; and, in 1 case, at thoracotomy for a persistent right hemothorax. In the remaining 50 patients (88%), the diagnosis was established within 24 hours. In 21 (42%) of these, the problem was initially recognized at the time of celiotomy for accompanying injuries. CONCLUSIONS: Blunt diaphragmatic injuries are easily missed in the absence of other indications for immediate surgery, since radiologic abnormalities of the diaphragm--particularly those involving the right hemidiaphragm--are often interpreted as thoracic trauma. In this setting, a high index of suspicion coupled with selective use of radionuclide scanning, ultrasound, and CT or magnetic resonance imaging is necessary for early detection of this uncommon injury.

Adolescent↗
PubMed1995

Culture, gender, and self: a perspective from individualism-collectivism research.

Individualism and collectivism are often equated with independent vs. interdependent, agentic vs. communal, and separate vs. relational self-construals. Although these same concepts have been used to characterize both cultural and gender differences, a perspective of cultural evolution suggests it is unlikely. A division of labor within society may produce gender differences, but this cannot explain cultural differences. A study of self-construal involving 5 cultures (Australia, the United States, Hawaii, Japan, and Korea) shows that differences between these cultures are captured mostly by the extent to which people see themselves as acting as independent agents, whereas gender differences are best summarized by the extent to which people regard themselves as emotionally related to others.

Adolescent↗
PubMed1995

Spindle waves are propagating synchronized oscillations in the ferret LGNd in vitro.

1. The cellular features of propagation of spindle waves and a bicuculline-induced slow oscillation through sagittal slices of the ferret dorsal lateral geniculate nucleus (LGNd) maintained in vitro were examined with simultaneous extracellular and intracellular recordings from up to eight sites. Spindle waves typically propagated along the long axis (dorsal-ventral) of the sagittal slice at a speed of 0.3-1.5 mm/s and were synchronized along the line of projection between the perigeniculate nucleus (PGN) and the A, A1, and C laminae. 2. Spindle waves can be initiated with local electrical stimulation or can occur spontaneously in any part of the LGNd/PGN. On initiation of a spindle wave, spindle waves propagate away from the site of initiation. Spindle waves may propagate only locally or may collide with other spindle waves. Collision of spindle waves is associated with synchronization of the two network oscillations, and the spindle waves do not propagate past one another. 3. Repetitive electrical stimulation reveals that spindle wave generation and propagation exhibit a relative refractory period of between 7 and 14 s in vitro. Stimulation at rates of less than the refractory period results in the generation of abbreviated local spindle waves at the stimulation site, but not in the propagation of this spindle wave into adjacent regions of the slice. 4. Local block of non-N-methyl-D-aspartate (non-NMDA) excitatory amino acid receptors in the PGN with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) prevents the propagation of spindle waves across the point of application, indicating that the excitation of PGN neurons by thalamocortical cells is essential to the propagation of these oscillations. The local antagonism of non-NMDA receptors in the PGN results in the dorsal and ventral aspects of the LGNd slice behaving as independent spindle wave generators, even if before application of CNQX they were not. 5. Activation of a burst discharge in a single PGN neuron can result in the generation of a full spindle wave and the propagation of this spindle wave both dorsally and ventrally through the slice away from the activated PGN neuron. The ability of a burst of action potentials in a PGN neuron to generate a spindle wave is suppressed immediately after the generation of a spindle wave, but slowly returns over a 7- to 14-s period corresponding to the relative spindle wave refractory period.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Molecular cloning of cDNA for double-stranded RNA adenosine deaminase, a candidate enzyme for nuclear RNA editing.

We have cloned human cDNA encoding double-stranded RNA adenosine deaminase (DRADA). DRADA is a ubiquitous nuclear enzyme that converts multiple adenosines to inosines in double-helical RNA substrates without apparent sequence specificity. The A --> I conversion activity of the protein encoded by the cloned cDNA was confirmed by recombinant expression in insect cells. Use of the cloned DNA as a molecular probe documented sequence conservation across mammals and detected a single transcript of 7 kb in RNA of all human tissues analyzed. The deduced primary structure of human DRADA revealed a bipartite nuclear localization signal, three repeats of a double-stranded RNA binding motif, and the presence of sequences conserved in the catalytic center of other deaminases, including a cytidine deaminase involved in the RNA editing of apolipoprotein B. These structural properties are consistent with the enzymatic signature of DRADA, and strengthen the hypothesis that DRADA carries out the RNA editing of transcripts encoding glutamate-gated ion channels in brain.

Adenosine Deaminase↗
PubMed1994

Purification and characterization of double-stranded RNA adenosine deaminase from bovine nuclear extracts.

The double-stranded RNA (dsRNA) adenosine deaminase (DRADA) deaminates adenosine residues to inosines and creates I-U mismatched base pairs in dsRNAs. Its involvement in RNA editing of glutamate-gated ion channel gene transcripts in mammalian brains has been proposed as one of the biological functions for this recently identified cellular enzyme. We purified a mixture of three forms, 93, 88, and 83 kDa, of bovine DRADA proteins, all likely to be active enzymes. We determined that DRADA has a native molecular mass of approximately 100 kDa, suggesting that the enzyme exists as a monomer. The purified enzyme was not inhibited by 2'-deoxycoformycin, a transition state analog inhibitor of adenosine deaminase and AMP deaminase, suggesting that the catalytic mechanism of DRADA might be different from that of other deaminases. DRADA binds specifically to dsRNA with a dissociation constant of 0.23 nM for a synthetic dsRNA, and the Michaelis constant is 0.85 nM. These values indicate that DRADA has a much higher affinity for its substrate than other deaminases such as adenosine deaminase and AMP deaminase. DRADA may need this extremely high affinity to catalyze efficiently the modification of relatively rare substrate RNAs in the cell nucleus.

Adenosine Deaminase↗
PubMed1994

Combined duodenal and colonic necrosis. An unusual sequela of caustic ingestion.

Two unusual cases of liquid caustic ingestion that resulted in gangrene of the duodenum and adjacent colon, and burns of the esophagus, stomach, and pancreas are presented. The routine evaluation of the oropharynx, esophagus, and stomach after liquid caustic ingestion can seriously underestimate the extent of injury to distal portions of the gastrointestinal (GI) tract, such as the colon and pancreas, that are not usually included in the initial evaluation of ingestion injuries. In stable patients managed nonoperatively, the entire upper GI tract, including the duodenum, must be visualized either by endoscopy or, less preferably, by barium series. Double-contrast computed tomography should be performed when significant duodenal injuries are present in order to inspect the colon, pancreas, and small bowel. With this approach, life-threatening, multi-organ, subdiaphragmatic ingestion injuries can be identified and treated early.

Adult↗
PubMed1993

Double-stranded RNA adenosine deaminase as a potential mammalian RNA editing factor.

Double-stranded RNA (dsRNA) adenosine deaminase, or DRADA, is a cellular enzyme that modifies adenosine residues to inosines in dsRNA by hydrolytic deamination, replacing A-U with mismatched I-U base pairs. Since it alters the base composition in its substrate RNA, one possible role played by DRADA is to participate in RNA editing. In this article, a brief review is given of characteristics of DRADA. Its possible involvement in RNA editing is also discussed in detail, including specific cases in which DRADA has been implicated as an RNA editing factor.

Adenosine Deaminase↗
PubMed1992

Pathway from the zona incerta to the superior colliculus in the rat.

In order to test the proposal that the zona incerta contributes to the generation of orienting movements, we examined the synaptic relationships between the incertotectal pathway and the cells of origin of the predorsal bundle. The predorsal bundle cells give rise to the major premotor pathway from the superior colliculus to the brainstem gaze centers. First, cytochrome oxidase histochemistry, gamma-aminobutyric acid (GABA), and glutamic acid decarboxylase (GAD) immunocytochemistry, and the axonal transport of markers were used to define the borders of a ventral subdivision of the zona incerta. This subdivision projects topographically to the same sublamina of the intermediate grey layer of the superior colliculus that contains the vast majority of the predorsal bundle cells. Experiments in which incertotectal cells were labeled by both retrograde transport and immunocytochemistry showed that this pathway is GABAergic. Retrograde and anterograde experiments also showed that this pathway is reciprocated by a pathway from the intermediate grey layer of the superior colliculus to the same ventral subdivision of the zona incerta. Finally, experiments combining axonal transport and electron microscopic methods showed that the incertotectal pathway is the source of a monosynaptic GABAergic input to the cells of origin of the predorsal bundle. The ventral subdivision of the zona incerta is contrasted with a second source of GABAergic input to the predorsal bundle cells, the substantia nigra pars reticulata.

Afferent Pathways↗
PubMed1991

Substrate specificity of the dsRNA unwinding/modifying activity.

Double-stranded RNA (dsRNA) unwinding/modifying activity, which is present in a wide range of eukaryotic cells, has been previously shown to convert up to 50% of adenosine residues to inosines within intermolecular dsRNA. In the present study, we report that this activity also modifies, though slightly less efficiently, intramolecular double-stranded regions of synthetic RNAs. Our results widen the range of the possible biological substrates for the activity since many stem and loop type RNA secondary structures (intramolecular dsRNA), present in eukaryotic as well as viral transcripts, can potentially serve as substrates. In addition, we have found that the dsRNA unwinding/modifying activity requires a double-stranded region of at least 15-20 base pairs (bp) for substrate recognition. Furthermore, modification efficiency was found to be critically dependent on the length of the double-stranded region; as the size decreased below 100 bp, it dropped precipitously. Our results suggest that efficient modification may occur only with relatively long (greater than 100 bp) dsRNA, perhaps because multiple copies of the enzyme must be bound.

Base Sequence↗