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Biomedical subjects

W Park

Publications and source records attributed to W Park.

At least 73 records · Page 4Linked to original sources
PubMed1996

MRI examination and monitoring of pediatric patients under sedation.

From April 1992 to May 1994, 780 patients aged from 1 day to 8 years were examined. Sedation of these patients was conducted by giving chlorprothixene orally and, in some cases, chloral hydrate had to be added. The patients were monitored with a pulse oxymeter. Investigations could begin after 50 -120 min. In 710 patients (91%) the first attempt to perform the examination was successful; 70 patients required one or two further attempts. Only two of the 780 patients (0.5%) showed evidence of respiratory depression. The total number of pediatric MRI examinations performed in 1 year is almost 1000. In the hands of an experienced pediatric radiologist these examinations can be performed entirely without anesthesia.

Child↗
PubMed1996

Inorganic pyrophosphate generation from adenosine triphosphate by cell-free human synovial fluid.

OBJECTIVE: To quantify inorganic pyrophosphate (PPi) production from extracellular adenosine triphosphate (ATP) by human synovial fluids (SF). METHODS: Serial measurements of ATP hydrolysis rate (t1/2) were performed by the luciferase method from a starting concentration of 500 nM in 21 pathologic and one normal cell-free SF samples incubated under physiologic conditions. ATP was then pumped into a sample of each fluid, using the rate constant derived from the t1/2 of that fluid, to provide steady state levels simulating those reported in SF. Trace [32P] gamma ATP was added at the start of the infusion; conversion to [32P] Pi and to [32P] PPi was determined by precipitation of Pi as reduced phosphomolybdate before and after treatment with yeast inorganic pyrophosphatase. Finally, the pumping experiment was repeated and PPi production was calculated from direct measurement of PPi at time zero and at 60 min. PPi hydrolysis was measured in each fluid by [32P] Pi precipitation from [32P] PPi tracer added at time zero. RESULTS: ATP was hydrolyzed by all SF. The mean t1/2 (seconds) in 8 osteoarthritis (OA) samples was 72 s, in 5 calcium pyrophosphate dihydrate (CPPD) 30 s (p < 0.02), in 3 rheumatoid arthritis (RA) 1160 s, in normal 86 s, in 3 olecranon bursal (OB) 54 s, and in 2 total knee replacement fluid samples 17 and 121 s. The major product of ATP hydrolysis was PPi in all but 2 fluids (1 RA, 1 OB), even at lower than steady state levels. At simulated in vivo steady state ATP levels, mean conversion of APT to PPi was stoichiometric in OA and CPPD fluids. PPi hydrolysis was < 4% in all noninflammatory fluids. CONCLUSION: PPi is the major product of extracellular ATP catabolism in most SF. Hydrolysis rates were significantly faster in SF containing CPPD crystals. Mean PPi production by these fluids at simulated in vivo steady state levels was 6-fold that of OA SF (p < 0.01). Hydrolysis of extracellular ATP by ectonucleotide pyrophosphohydrolases can account for all PPi produced by joint issues previously estimated from [32P] PPi pool and turnover studies in human knee joints.

Adenosine Triphosphate↗
PubMed1996

Generation of inorganic pyrophosphate from extracellular adenosine triphosphate by human serum and plasma.

OBJECTIVE: To quantify inorganic pyrophosphate (PPi) production from extracellular adenosine triphosphate (ATP) by human serum or plasma. METHODS: Serial measurements of ATP hydrolysis (t1/2) were performed by the luciferase method from a starting concentration of 1 microM in serum or platelet-poor plasma incubated under physiologic conditions. ATP was then pumped into another sample of each specimen using the rate constant derived from the ATP t1/2 of that specimen. Trace (32P) gamma ATP was added at the start of the infusion; conversion to (32P) inorganic orthophosphate (Pi) and to (32P) PPi was determined by precipitation of Pi as reduced phosphomolybdate before and after treatment with yeast pyrophosphatase. RESULTS: ATP was hydrolyzed by all serum and plasma specimens; the rate of hydrolysis in serum and plasma from the same blood sample was nearly identical. PPi was the major product, averaging 71%. CONCLUSION: PPi is the major product of ATP catabolism in serum and platelet-poor plasma.

Adenosine Triphosphate↗
PubMed1996

Identification of a variant estrogen receptor lacking exon 4 and its coexpression with wild-type estrogen receptor in ovarian carcinomas.

By means of reverse transcription-PCR we have identified an alternatively spliced mRNA coding for a variant estrogen receptor (ER) that lacks exon 4 (ERDelta4) and is coexpressed with the wild-type ER mRNA in ovarian carcinomas. Furthermore, Western blot analysis revealed the expression of the ERDelta4 protein in normal as well as neoplastic ovarian tissues along with the wild-type ER, although the relative amounts of the wild-type ER and ERDelta4 proteins varied. The trans-activational properties of this variant were studied in ER-negative COS1 cell lines by cotransfection of the ERDelta4 expression vector and a reporter gene containing the estrogen response element. The ERDelta4 protein was not able to activate transcription of a reporter gene. However, it inhibited estrogen-dependent transcriptional activation in a dominant negative fashion when it was cotransfected with the wild-type ER and reporter plasmid. Because it has been shown that ERDelta4 is not able to bind to its response element, the observed inhibitory effect probably occurs through protein-protein interactions. Although several variants of the ER have been described from cancerous cells, none has been identified in ovarian tissues, and ERDelta4 is the only isoform detected in normal tissues. These results may have implications for understanding the physiological role of ERDelta4 in normal cells, because it may affect the function of the wild-type ER, depending on the level of the variant ER protein relative to that of the wild-type ER.

Alternative Splicing↗
PubMed1995

Analysis of interaction between Ras and CDC25 guanine nucleotide exchange factor using yeast GAL4 two-hybrid system.

Our results demonstrate that the GAL4 two-hybrid system can be useful for studying interactions of the wild-type and mutant forms of Ras proteins with the CDC25 guanine nucleotide exchange factor (CDC25-GEF). In addition, our findings show that a negative result in the GAL4 two-hybrid system does not indicate that the two proteins tested do not interact under all conditions but only that they do not interact under the specific conditions examined. We recommend that the two-hybrid system be employed in combination with other approaches, including molecular genetic analyses and in vitro binding experiments, for the study of Ras and CDC25-GEF interactions.

Amino Acid Sequence↗
PubMed1995

Discrepancy of recovery times related to potency between atracurium and mivacurium simultaneously administered in isolated forearms.

Recovery from potent non-depolarising muscle relaxants is slower than from the less potent agents. However, recovery from mivacurium, which is more potent than atracurium, is faster than from atracurium following systemic administration. In an attempt to confirm this discrepancy we compared recovery times following simultaneous administration of equipotent doses of atracurium and mivacurium into the isolated forearms of human volunteers (n = 10). This method enabled us to study the interaction of muscle relaxants with receptors at the neuromuscular junction separated from the effects of plasma drug concentration. In these experiments, the recovery times from maximum block to 50% recovery of control twitch height were significantly longer with mivacurium than with atracurium (mean 25.2(SD 4.7) versus 22.6(3.1) min, p < 0.01). We found that the evidence that mivacurium has a slower recovery than the less potent atracurium may be true using the bilateral, isolated forearm technique and that the discrepancy might be due to a difference in the pharmacokinetic variables of the two drugs.

Adult↗
PubMed1994

Cloning and analysis of human cDNAs encoding a 140-kDa brain guanine nucleotide-exchange factor, Cdc25GEF, which regulates the function of Ras.

Ras proteins bound to GDP are biologically inactive while those bound to GTP are active. Ras-specific guanine nucleotide-exchange factors (GEFs) have been shown to activate Ras proteins. We used oligodeoxyribonucleotide primers with sequences similar to the cDNAs of rat and mouse cdc25 (encoding a Ras-GEF) to amplify, by the PCR, sequences with the potential to encode a 1275-amino-acid protein homologous to the rodent Cdc25GEF proteins. Northern blot analysis detected a brain-specific 5-kb transcript. We provide evidence for a novel alternately spliced transcript of cdc25 and show that these alternately spliced transcripts are differentially expressed in various regions of the adult nervous system. Antibodies raised against the C terminus of the protein recognize a 140-kDa protein in brain extracts of human, rat, guinea pig and cow; the 140-kDa protein is associated predominantly, if not exclusively, with a crude membrane fraction of brain. The C terminus of human Cdc25GEF can complement the loss of CDC25 function in Saccharomyces cerevisiae. A glutathione S-transferase fusion protein containing the C terminus of the cdc25 product can stimulate guanine nucleotide exchange on H-Ras in vitro. Further, the Cdc25-fusion protein binds tightly to the nucleotide-free form of H-Ras in vitro, and this binding is reversed by the addition of GTP.

Alternative Splicing↗
PubMed1994

Membrane-targeting potentiates guanine nucleotide exchange factor CDC25 and SOS1 activation of Ras transforming activity.

Growth factor-triggered activation of Ras proteins is believed to be mediated by guanine nucleotide exchange factors (CDC25/GRF and SOS1/2) that promote formation of the active Ras GTP-bound state. Although the mechanism(s) of guanine nucleotide exchange factor regulation is unclear, recent studies suggest that translocation of SOS1 to the plasma membrane, where Ras is located, might be responsible for Ras activation. To evaluate this model, we generated constructs that encode the catalytic domains of human CDC25 or mouse SOS1, either alone (designated cCDC25 and cSOS1, respectively) or terminating in the carboxyl-terminal CAAX membrane-targeting sequence from K-Ras4B (designated cCDC25-CAAX and cSOS1-CAAX, respectively; in CAAX, C is Cys, A is an aliphatic amino acid, and X is Ser or Met). We then compared the transforming potential of cCDC25 and cSOS1 with their membrane-targeted counterparts. We observed that addition of the Ras plasma membrane-targeting sequence to the catalytic domains of CDC25 and SOS1 greatly enhanced their focus-forming activity (10- to 50-fold) in NIH 3T3 transfection assays. Similarly, we observed that the membrane-targeted versions showed a 5- to 10-fold enhanced ability to induce transcriptional activation from the Ets/AP-1 Ras-responsive element. Furthermore, whereas cells that stably expressed cCDC25 or cSOS1 exhibited the same morphologies as untransformed NIH 3T3 cells, cells expressing cCDC25-CAAX or cSOS1-CAAX displayed transformed morphologies that were indistinguishable from the elongated and refractile morphology of oncogenic Ras-transformed cells. Thus, these results suggest that membrane translocation alone is sufficient to potentiate guanine nucleotide exchange factor activation of Ras.

3T3 Cells↗
PubMed1994

Amino acid residues in the CDC25 guanine nucleotide exchange factor critical for interaction with Ras.

Previously we found that negatively charged residues at positions 62, 63, and 69 of H-Ras are involved in binding to the CDC25 guanine nucleotide exchange factor (GEF). Using site-directed mutagenesis, we have changed conserved, positively charged residues of CDC25GEF to glutamic acid. We find the nonfunctional CDC25R1374E mutant and the nonfunctional H-RasE63K mutant cooperate in suppression of the loss of CDC25 function in Saccharomyces cerevisiae. Also, peptides corresponding to residues 1364 to 1383 of CDC25GEF inhibit interaction between GEFs and H-Ras. We propose that residues 1374 of CDC25GEF and 63 of H-Ras form an ion pair and that when this ion pair is reversed, functional interaction can still occur.

Humans↗
PubMed1992

Evaluation of finger blood flow with Tc-99m MDP (methylene diphosphonate).

BACKGROUND: A variety of methods were used to establish objective diagnostic criteria of Raynaud's phenomenon. We intended to introduce another method, using radionuclide (Tc-99m methylene diphosphonate) scintigraphy, which is more objective, simple and economical than the past methods. METHODS: The finger blood flow with radionuclide scintigraphy was evaluated in 10 patients of Raynaud's syndrome, 12 patients of connective disease without Raynaud's symptoms, and 20 normal persons. After immersing one hand in ice water (4 degrees C) for 30 seconds, the hand was exposed to 22 degrees C room air for 15 minutes, and then the patients received the intravenous (IV) bolus of 20 microCi of Tc-99m methylene diphosphonate (MDP). At the same time, scintigraphic image of both hands started with the region of interest, including the second, third, fourth and fifth fingers distal to the metacarpophalangeal (MCP) joints. Computer recording of the counts in the region of interest every 2 seconds for 310 seconds was started on IV bolus injection. RESULTS: The 310 seconds cumulative digital blood flow ratio of cold exposed hand to room air exposed hand was significantly lower in Raynaud's group (p < 0.001), and the ratio of initial slope of activity curve was also lower in the Raynaud's group (p < 0.001). Of the 8 patients showing Raynaud's syndrome, 4 patients of scleroderma and 1 patient of multiple myeloma showed no improvement of finger blood flow in the cold exposed hand after 2 weeks of pharmacological therapy, but 1 patient of mixed connective tissue disease, 1 patient of Behcet's syndrome and 1 patient of SLE showed much improved finger blood flow after combined administration of vasodilator, calcium channel blockers and antiplatelet drugs. CONCLUSIONS: The evaluation of finger blood flow with 99mTc-MDP could be considered to be one of the simple, economical and new methods that can be used in the follow-up, objective assessment of therapeutic effect, and giving an aid in the study of the pathophysiology of the Raynaud's phenomenon.

Adult↗