Search PubMed⌕ Search

Biomedical subjects

H Cho

Publications and source records attributed to H Cho.

At least 109 records · Page 6Linked to original sources
PubMed1998

Cerebral monitoring by means of oximetry and somatosensory evoked potentials during carotid endarterectomy.

OBJECT: Cerebral ischemia that occurs during carotid endarterectomy is commonly monitored by means of somatosensory evoked potentials (SSEPs) and electroencephalography (EEG). The authors conducted this study to determine whether cerebral ischemia could also be reliably detected by cerebral oximetry. METHODS: Twenty-nine patients who underwent carotid endarterectomy were monitored by means of SSEPs, EEG, and cerebral oximetry with a model NIRO500 (20 patients) or INVOS3100A (nine patients) oximeter. Changes in amplitude of SSEPs were graded as follows: 0, no change; 1, decrease of less than 50%; 2, decrease of greater than 50%; and 3, 100% decrease. As measured with the NIRO500 oximeter, closing the common caro-tid artery decreased mean oxyhemoglobin levels twice as much (p < 0.005) in the group with SSEPs of 1 to 3 (-13.11+/-5.59 microM [mean+/-standard deviation], 12 patients) as in the group with SSEPs of 0 (-6.22+/-5.59 microM, eight patients). The rise in deoxyhemoglobin was also greater (p < 0.05). Two of nine patients monitored with the INVOS3100A oximeter had SSEPs of 1 and 3, and their regional saturation of oxygen (rSO2) values fell by -11.50 and -11.51, respectively. In the remaining seven patients with SSEPs of 0, the rSO2 ranged between -2.00 and -6.10 with no overlap with the group with SSEPs of I to 3. The increase in oxyhemoglobin monitored using the NIRO500 oximeter and rSO2 monitored using the INVOS3100A machine after opening the external carotid artery was less than that seen after opening the internal carotid artery. Both types of oximeters could detect cerebral ischemia but whereas false negatives occurred with the NIRO500, none was observed with the INVOS3100A. Extracranial contamination was also four times less frequent with the INVOS3100A than with the NIRO500 monitor. CONCLUSIONS: The results indicate that at least as measured with the INVOS3100A instrument, a decrease in rSO2 of -10 or more or a decrease below an rSO2 of 50 is indicative of cerebral ischemia of sufficient severity to decrease the amplitude of SSEPs.

Brain Ischemia↗
PubMed1998

Desmoplastic cerebral astrocytoma of infancy: a case report.

We present a case of desmoplastic cerebral astrocytoma of infancy (DCAI) in a 9-month-old boy including immunohistochemical and proliferative activity studies. It was mainly composed of glial fibrillary acidic protein (GFAP)-positive astrocytes and desmoplastic stroma. Studies with Ki-67 and synthetic phase fraction disclosed a low proliferative activity. Flow cytometric study revealed diploidy pattern. These findings suggest a positive correlation with the favorable prognosis.

Astrocytoma↗
PubMed1998

Features for a B-ISDN telemedicine system and its application.

Telemedicine technology is emerging as a new way of medical practice. It will provide more cooperative activity between departments and more comfortable access for disabled patients home. We developed two types of telemedicine system: a telediagnosis system and a home care system. Our telemedicine application is aimed to be run on the broadband-integrated services digital network (B-ISDN). The legacy network is also considered. The user interface is designed to help doctors to communicate easily. The key elements of telemedicine systems are user friendly interface, medical multimedia database design highly refined display technique.

Computer Communication Networks↗
PubMed1998

Toward clinical end-user computing: programmable order protocols for efficient human computer interaction.

We have developed and implemented an efficient method of managing routine patient care information as a programmable group order protocol. The purpose of protocol is to minimize a labor-intensive manual computer interaction by grouping clinically related routine orders as a single entity, thus to greatly speed up the time taken for manual entry such as keyboard stroke and/or mouse clicking. User programmability is added to facilitate insertion, deletion and update of order items to be a locally independent operation. A sequence of menu screen is also programmable when a change of standard operation is needed. Department specific order protocols are classified into four categories to improve user convenience. The degree of efficiency is measured by a number of key strokes and entry time. In most cases the time to enter order protocol with correction is found to take less than one minute with less than five key strokes. The method of order protocol entry clearly demonstrates end-user computing capability so that department specific requirements are resolved without resorting to computer department personnel. Flexibility of managing individual physician specific protocols is also beneficial enough to enhance the morale toward a hospital information system currently in use.

Computer Graphics↗
PubMed1998

Study of user preference of graphic user interface in laboratory information system.

In order to elucidate employees satisfaction levels in using graphic user interface. (GUI) in a laboratory information system (LIS), users attitudes toward GUI versus CUI. (Character User Interface) in a similar LIS were surveyed one month after implementing upgraded version of LIS in a tertiary care university hospital laboratory. The outcome of the study showed that approximately two third of users preferred to have GUI in LIS. There was no difference in preference of GUI of users whether they had previous experience with GUI or not. However the female and older employees tend to shy away from GUI. The employee productivity was improved with GUI although it takes slightly longer program loading time than that of CUI. In conclusion, the laboratory employee satisfaction was higher with GUI than CUI and their productivity was improved with GUI.

Adult↗
PubMed1997

Mammalian capping enzyme complements mutant Saccharomyces cerevisiae lacking mRNA guanylyltransferase and selectively binds the elongating form of RNA polymerase II.

5'-Capping is an early mRNA modification that has important consequences for downstream events in gene expression. We have isolated mammalian cDNAs encoding capping enzyme. They contain the sequence motifs characteristic of the nucleotidyl transferase superfamily. The predicted mouse and human enzymes consist of 597 amino acids and are 95% identical. Mouse cDNA directed synthesis of a guanylylated 68-kDa polypeptide that also contained RNA 5'-triphosphatase activity and catalyzed formation of RNA 5'-terminal GpppG. A haploid strain of Saccharomyces cerevisiae lacking mRNA guanylyltransferase was complemented for growth by the mouse cDNA. Conversion of Lys-294 in the KXDG-conserved motif eliminated both guanylylation and complementation, identifying it as the active site. The K294A mutant retained RNA 5'-triphosphatase activity, which was eliminated by N-terminal truncation. Full-length capping enzyme and an active C-terminal fragment bound to the elongating form and not to the initiating form of polymerase. The results document functional conservation of eukaryotic mRNA guanylyltransferases from yeast to mammals and indicate that the phosphorylated C-terminal domain of RNA polymerase II couples capping to transcription elongation. These results also explain the selective capping of RNA polymerase II transcripts.

Amino Acid Sequence↗
PubMed1997

Expression of androgen receptor and its implication in hepatoma cells.

Hepatocellular carcinoma (HCC) in human and murine has been known to occur more frequently in male than female. Attempts have been made to find a possible mechanism of increased growth advantage in the HCC cells by testosterone (T). Treatment of HepG2 human HCC cells with T increased DNA synthesis by 30-50%, whereas T increased it by 10-30% in FaO (rat) cells. Androgen receptor (AR) levels in HepG2 and FaO cells were 94.1 fmol/mg protein and 55.0 fmol/mg protein, respectively. Expression of AR mRNA species was detected as about 10 kb (doublet) in HepG2. On the other hand, much less expression of AR mRNA was observed in FaO cells. AR signals around 28S rRNA (4.7 kb) and the small size RNAs detected in the total cellular RNAs were not found in the poly(A) + RNAs isolated from the cells. Contrary to the earlier observation by other investigators, expression of hepatic AR was not down-regulated by T until 72 h of treatment. These results demonstrate one of the modes of action by T for the preferential development of HCC in male.

Animals↗
PubMed1997

Affinity purification of a human RNA polymerase II complex using monoclonal antibodies against transcription factor IIF.

Five different monoclonal antibodies that immunoreact with RAP74, the large subunit of general transcription factor (TF) IIF, were produced and characterized. Using one of these antibodies, an affinity purification procedure was devised to isolate a human RNA polymerase II complex. This procedure is fast, simple, and reproducible and does not require extensive purification. The RNA polymerase II complex isolated using this procedure contains SRB (suppressor of RNA polymerase B) polypeptides, transcription factors IIE and IIF, limiting amounts of TFIIH, and the TATA-binding protein, but was devoid of TFIIB.

Amino Acid Sequence↗
PubMed1997

Flexibility of liver alcohol dehydrogenase in stereoselective binding of 3-butylthiolane 1-oxides.

Thiolane 1-oxides are analogs of the carbonyl substrates that bind to the alcohol dehydrogenase-NADH complex and are potent uncompetitive inhibitors against alcohol [Chadha, V. K., et al. (1985) J. Med. Chem. 28, 36-40]. The four stereoisomers of 3-butylthiolane 1-oxide (BTO) were separated by chiral phase chromatography. CD and 1H-NMR spectra identified the enantiomeric pairs. 1H-NMR chemical shifts were assigned on the basis of COSY spectra of both diastereoisomers and confirmed by HMQC spectra. Coupling constants were determined through one-dimensional decoupling experiments. NMR with chiral shift reagents, Eu(hfc)3 [europium tris [3-[(heptafluoropropyl)hydroxymethylene]-(+)-camphorate]] or (R)-(-)-N-(3,5-dinitrobenzoyl)-alpha-methylbenzylamine, determined that the most inhibitory isomer is either 1S,3R or 1R,3S. The chemical shifts of protons in the thiolane 1-oxide ring were influenced by the whole structure and were not correlated with the computed Mulliken charges. X-ray crystallography at 2.1 and 1.66 A resolution of the ternary enzyme complexes with NADH demonstrated that the absolute configuration of the most inhibitory (Kii = 0.31 microM) stereoisomer is 1S,3R and the next best inhibitor (Kii = 0.73 microM) is 1S,3S. The thiolane 1-oxide rings bind in the same position, in the substrate binding site, but the geometry of the complexes suggests that the sulfoxides are not transition state analogs. Significantly, the butyl groups of the two isomers are accommodated differently by flexible amino acid side chains adopting alternative rotameric conformations.

Alcohol Dehydrogenase↗
PubMed1997

Porous high-density polyethylene implants in auricular reconstruction.

OBJECTIVE: To evaluate the ability of porous high-density polyethylene (Medpor) implants to tolerate exposure and support skin grafts when used to reconstruct defects in auricular cartilage in an animal model. DESIGN: Polyethylene implants placed in surgically created defects in auricular cartilage and covered with a skin flap were then exposed at either 4, 7, or 21 days after implantation. The exposed implants were then allowed to heal secondarily or received a skin graft 1 week later. The ability of polyethylene implants to tolerate exposure and support skin grafts was observed clinically and via histological study of the implantation sites. SUBJECTS: Nine adult New Zealand rabbits. RESULTS: Polyethylene implants demonstrated excellent ability to tolerate wound exposure as early as 4 days after implantation, with extrusion of 1 of the 36 implants placed. The degree of secondary wound healing increased as the interval from implantation to exposure increased from 4 to 21 days. Exposed polyethylene implants in all groups also supported all 18 skin grafts placed 1 week after exposure of the implant surface. CONCLUSIONS: Polyethylene implants are well tolerated as replacements for native cartilage in auricular reconstruction. Polyethylene implants tolerated wound exposure as early as 4 days after implantation and demonstrated the ability to heal by secondary intention and support skin grafts. This is likely because of the extent of fibrovascular ingrowth from surrounding tissue, which allows the material to behave more like native tissue and less like a foreign body in this setting.

Animals↗
PubMed1997

Cyclic changes in NMDA receptor activation in hippocampal CA1 neurons after ischemia.

We studied N-methyl-D-aspartate (NMDA) receptor-mediated synaptic potentials in CA1 pyramidal neurons using hippocampal slices of gerbils after transient forebrain ischemia. In the presence of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and bicuculline, stimulation of Schaffer collateral/commissural fibers induced field excitatory postsynaptic potentials (fEPSP) activated by NMDA receptors. We found that in many slices after ischemia, prolonged low-frequency stimulation (0.1-10 Hz) caused repeated depression and potentiation of the NMDA-mediated fEPSP. Changes in fEPSP amplitude were dependent on stimulus frequency and the cycle frequency ranged from 0.08 to 2.5 cycles/min. These cyclic changes were blocked by application of BAPTA-AM, a membrane-permeable Ca2+ chelator, but were little affected by application of verapamil or by lowering the Ca2+ in bathing solution. Intracellular recordings from CA1 neurons revealed that low-frequency stimulation caused periodic depolarizations of membrane potential accompanied by depression of the excitatory postsynaptic potentials. The cyclic changes of fEPSPs were blocked by inhibitors of protein kinase C (PKC) but were unaffected by inhibitors of Ca2+/calmodulin-dependent protein kinase II (CaMKII) or myosin light-chain kinase (MLCK). These results suggest that stimulus-dependent NMDA-receptor activation, mediated by PKC, takes place in the postischemic CA1 neurons and that the cyclic change may reflect abnormal intracellular Ca2+ signaling processes leading to neuronal degeneration.

Animals↗
PubMed1997

The human immunodeficiency virus transactivator Tat interacts with the RNA polymerase II holoenzyme.

The human immunodeficiency virus (HIV) encodes a transcriptional transactivator (Tat), which binds to an RNA hairpin called the transactivation response element (TAR) that is located downstream of the site of initiation of viral transcription. Tat stimulates the production of full-length viral transcripts by RNA polymerase II (pol II). In this study, we demonstrate that Tat coimmunoprecipitates with the pol II holoenzyme in cells and that it binds to the purified holoenzyme in vitro. Furthermore, Tat affinity chromatography purifies a holoenzyme from HeLa nuclear extracts which, upon addition of TBP and TFIIB, supports Tat transactivation in vitro, indicating that it contains all the cellular proteins required for the function of Tat. By demonstrating that Tat interacts with the holoenzyme in the absence of TAR, our data suggest a single-step assembly of Tat and the transcription complex on the long terminal repeat of HIV.

Animals↗
PubMed1997

Extracellular ATP-induced Ca2+ mobilization of type I spiral ganglion cells from the guinea pig cochlea.

Intracellular calcium concentrations ([Ca2+]i) in type I cochlear spiral ganglion cells (SGCs) of the guinea pig were measured by digital imaging microscopy and the Ca(2+)-sensitive dye Fura-2. Extracellular ATP induced elevation of [Ca2+]i in type I SGCs in a concentration-dependent manner. The ATP-induced elevation of [Ca2+]i in SGC was even evident in the Ca(2+)-free solution, thereby suggesting that ATP induces a Ca(2+)-release from intracellular stores in SGCs. Suramin and reactive blue 2, both antagonists for the P2-purinergic receptor, inhibited the [Ca2+]i increase in SGCs induced by extracellular ATP in a dose-dependent manner. Adenosine did not induce any changes of [Ca2+]i in SGC. These results suggest that type I SGCs may possess P2-purinergic receptor but not P1-purinergic receptor. Extracellular ATP induced a [Ca2+]i increase in type I SGCs, with and without neuritic processes, while L-glutamate increased [Ca2+]i in type I SGCs with neuritic processes, but not SGCs without neuritic processes. The ATP-induced [Ca2+]i increase was almost equal in both soma and processes. Therefore, the distribution of P2-purinergic receptor in type I SGCs may be homogeneous in soma and processes. Based on these observations, we suggest that extracellular ATP may act as a neurotransmitter or neuromodulator of the hair cell-afferent nerve synapse in the guinea pig cochlea.

Adenosine↗
PubMed1996

Synthesis and selective coronary vasodilatory activity of 3,4-dihydro-2,2-bis(methoxymethyl)-2H-1-benzopyran-3-ol derivatives: novel potassium channel openers.

A variety of compounds having a benzopyran such as levcromakalim generally exhibit potent antihypertensive activity. During extensive investigations aimed toward identifying K+ channel openers having selective coronary vasodilation without potent hypotensive and tachycardiac effects, we synthesized a series of 3,4-dihydro-2H-1-benzopyran-3-ol derivatives modified at positions 2, 4, and 6 in the benzopyran ring. Initially, compounds having two methoxymethyl groups at position 2 were found to show a selective effect on coronary blood flow (CoBF) relative to mean arterial pressure (MAP) in anesthetized dogs. To find more potent vasodilators, various benzopyran derivatives modified at position 4 were synthesized and structure-activity relationships were examined by evaluation of the extent and duration of the increase in CoBF in anesthetized dogs. As a result, compounds having a (1,6-dihydro-6-oxopyridazin-3-yl)amino group at position 4, in addition to the two methoxymethyl groups at position 2, were found to be more potent and to have an improved duration of action. Among these compounds, JTV-506, (-)-(3S,4R)-6-cyano-3,4-dihydro-4-[(1,6-dihydro-1-methyl-6-oxopyridaz in-3-yl)amino]-2,2-bis(methoxymethyl)-2H-1-benzopyran-3-ol, exhibited good selectivity for its effect. Administration of this compound (0.03 mg/kg, p.o.) elicited an increase of CoBF without a change of systemic blood pressure and heart rate (HR) in conscious dogs. Further evaluation was performed with respect to (i) the selectivity of its action on the coronary artery versus the aorta and (ii) its effects on MAP, HR, and electrocardiographic ST elevation. As a result, JTV-506 was selected as a potent and selective coronary vasodilator with various pharmacological features favoring clinical development.

Animals↗
PubMed1996

Inducible nitric oxide synthase requires both the canonical calmodulin-binding domain and additional sequences in order to bind calmodulin and produce nitric oxide in the absence of free Ca2+.

All three mammalian isoforms of nitric oxide synthase (NOS) must bind calmodulin (CaM) for enzymatic activity. Only NOS2 (the inducible isoform, iNOS) does so at the low levels of free Ca2+ in resting cells and when almost all Ca2+ is chelated in cell-free preparations. To test directly whether the predicted CaM-binding region of mouse NOS2 accounts for its Ca2+ independence, we prepared chimeric NOS's in which mouse NOS2 residues 503-532 were reciprocally exchanged with the corresponding residues 725-754 of rat NOS1 (neuronal NOS). Unlike either parent, both chimeras required an intermediate level of free Ca2+ to bind CaM and generate NO. In cell lysates, the concentration of Ca2+ necessary for half-maximal activity (EC50) was approximately 0 for NOS2, 200-300 n for NOS1, and 7-10 n for the chimeras. Results were similar when the region exchanged was enlarged by 7-8 residues toward the amino terminus. In contrast, when the carboxyl-terminal half of NOS2 (residues 454-1144) was replaced with that of NOS1 (residues 675-1429), the resulting chimera resembled NOS1 (EC50, 200-300 n free Ca2+). Truncation analysis suggested that NOS2 residues within the sequence 484-726 were required for Ca2+-independent CaM-binding. Thus, both the canonical CaM-binding domain and additional residues within the region 484-726 are necessary for NOS2's ability to bind CaM and produce NO when Ca2+ levels approach zero.

Amino Acid Sequence↗
PubMed1996

Human cyclin-dependent kinase-activating kinase exists in three distinct complexes.

Transcription factor IIH (TFIIH) is a multisubunit complex required for transcription and for DNA nucleotide excision repair. TFIIH possesses three enzymatic activities: (i) an ATP-dependent DNA helicase, (ii) a DNA-dependent ATPase, and (iii) a kinase with specificity for the carboxyl-terminal domain of RNA polymerase II. The kinase activity was recently identified as the cdk (cyclin-dependent kinase) activating kinase, CAK, composed of cdk7, cyclin H, and MAT-1. Here we report the isolation and characterization of three distinct CAK-containing complexes from HeLa nuclear extracts: CAK, a novel CAK-ERCC2 complex, and TFIIH. CAK-ERCC2 can efficiently associate with core-TFIIH to reconstitute holo-TFIIH transcription activity. We present evidence proposing a critical role for ERCC2 in mediating the association of CAK with core TFIIH subunits.

Cyclin-Dependent Kinases↗
PubMed1996

Cyclin C/CDK8 is a novel CTD kinase associated with RNA polymerase II.

A number of cyclin/kinase complexes have been identified in mammalian cells that are essential for controlled cell proliferation. Cyclin C was isolated by virtue of its ability to rescue the triple CLN mutation in yeast; however, until now its function has remained unclear. Cyclin C associates with a novel cyclin dependent kinase, CDK8, and we demonstrate that this complex is associated with kinase activity towards the carboxy-terminal domain (CTD) of RNA polymerase II. We have identified at least two distinct cyclin C/CDK8 containing complexes within the cell, a larger complex over 500 kD in size, that also contains the largest subunit of RNA polymerase II, and a smaller 170 kD species. Both of these cyclin C complexes retain potent CTD kinase activity. We further demonstrate that the cyclin C/CDK8 complex associates with the large subunit of RNA polymerase II in vivo, implicating a potential role for cyclin C/CDK8 in regulating its activities.

Amino Acid Sequence↗