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J C Boyer

Publications and source records attributed to J C Boyer.

At least 19 recordsLinked to original sources
PubMed2004

Visible upconversion emission of Pr3+ doped gadolinium gallium garnet nanocrystals.

The luminescence properties of a Pr3+-doped gadolinium gallium garnet (GGG, Gd3Ga5O12) nanocrystalline host were investigated. Dominant blue/green emission was observed emanating from the 3P0 --> 3H4 transition after excitation using a wavelength of 457.9 nm. Continuous wave excitation into the 1D2 level of the Pr3+ ion at 606.9 nm transition produced blue upconversion luminescence spectra, ascribed to emission from the 3P1 --> 3H4 and 3P0 --> 3H4 transitions. The increase in the decay times of the observed transitions following excitation with 606.9 nm is indicative of the dominance of an energy transfer upconversion (ETU) mechanism relative to excited state absorption (ESA). Furthermore, blue, green and red upconversion emission was observed from the 3P0, 3P1 and 1D2 states following excitation into the 1G4 energy level with 980 nm. No change in the decay times of the emitting states was observed following excitation with a wavelength of 980 or 457.9 nm; hence, upconversion was determined to primarily occur through ESA. The luminescence properties of the nanocrystals are compared to a single crystal of GGG:Pr3+ (bulk) with an identical Pr3+ concentration (1%).

Crystallization↗
PubMed2001

Microsatellite mutation rates are equivalent in normal and telomerase-immortalized human fibroblasts.

Telomerase-expressing human fibroblasts generally have the same properties as normal cells, except that they have an indefinite life span in culture. We have introduced a dinucleotide repeat sequence into the telomerase-expressing hTERT-1604 cell line and characterized the rates and types of frameshift mutations within this microsatellite. These data have been compared with those in diploid fibroblasts with a finite life span. The rates of mutation were found to be similar in the two cell types, indicating that DNA mismatch repair and other cellular processes responsible for maintenance of mutational stability are not disrupted by telomerase immortalization.

Cell Line, Transformed↗
PubMed2001

The yeast mutant vps5Delta affected in the recycling of Golgi membrane proteins displays an enhanced vacuolar Mg2+/H+ exchange activity.

Growth of the yeast vacuolar protein-sorting mutant vps5Delta affected in the endosome-to-Golgi retromer complex was more sensitive to Mg2+-limiting conditions than was the growth of the wild-type (WT) strain. This sensitivity was enhanced at acidic pH. The vps5Delta strain was also sensitive to Al3+, known to inhibit Mg2+ uptake in yeast cells. In contrast, it was found to be resistant to Ni2+ and Co2+, two cytotoxic analogs of Mg2+. Resistance to Ni2+ did not seem to result from the alteration of plasma-membrane transport properties because mutant and WT cells displayed similar Ni2+ uptake. After plasma-membrane permeabilization, intracellular Ni2+ uptake in vps5Delta cells was 3-fold higher than in WT cells, which is consistent with the implication of the vacuole in the observed phenotypes. In reconstituted vacuolar vesicles prepared from vps5Delta, the rates of H+ exchange with Ni2+, Co2+, and Mg2+ were increased (relative to WT) by 170%, 130%, and 50%, respectively. The rates of H+ exchange with Ca2+, Cd2+, and K+ were similar in both strains, as were alpha-mannosidase and H+-ATPase activities, and SDS/PAGE patterns of vacuolar proteins. Among 14 other vacuolar protein-sorting mutants tested, only the 8 mutants affected in the recycling of trans-Golgi network membrane proteins shared the same Ni2+ resistance phenotype as vps5Delta. It is proposed that a trans-Golgi network Mg2+/H+ exchanger, mislocalized to vps5Delta vacuole, could be responsible for the phenotypes observed in vivo and in vitro.

Antiporters↗
PubMed2001

Mechanical properties of coronary stents determined by using finite element analysis.

The mechanical function of a stent deployed in a damaged artery is to provide a metallic tubular mesh structure. The purpose of this study was to determine the exact mechanical characteristics of stents. In order to achieve this, we have used finite-element analysis to model two different type of stents: tubular stents (TS) and coil stents (CS). The two stents chosen for this modeling present the most extreme mechanical characteristics of the respective types. Seven mechanical properties were studied by mathematical modeling with determination of: (1) stent deployment pressure, (2) the intrinsic elastic recoil of the material used, (3) the resistance of the stent to external compressive forces, (4) the stent foreshortening, (5) the stent coverage area, (6) the stent flexibility, and (7) the stress maps. The pressure required for deployment of CS was significantly lower than that required for TS, over 2.8 times greater pressure was required for the tubular model. The elastic recoil of TS is higher than CS (5.4% and 2.6%, respectively). TS could be deformed by 10% at compressive pressures of between 0.7 and 1.3 atm whereas CS was only deformed at 0.2 and 0.7 atm. The degree of shortening observed increases with deployment diameter for TS. CS lengthen during deployment. The metal coverage area is two times greater for TS than for CS. The ratio between the stiffness of TS and that of CS varies from 2060 to 2858 depending on the direction in which the force is applied. TS are very rigid and CS are significantly more flexible. Stress mapping shows stress to be localized at link nodes. This series of finite-element analyses illustrates and quantifies the main mechanical characteristics of two different commonly used stents. In interventional cardiology, we need to understand their mechanisms of implantation and action.

Angioplasty↗
PubMed2001

Contraction of human colonic circular smooth muscle cells is inhibited by the calcium channel blocker pinaverium bromide.

UNLABELLED: The effects of L-type calcium channel blockers (CCBs) selective for the gastrointestinal tract (pinaverium) or non-selective (nicardipine and diltiazem), were investigated on CCK-, CCh- or KCl-induced contraction of smooth muscle cells (SMC) isolated from the circular muscle layer of normal or of inflamed human colons. In the normal tissue colon, whatever the contractile agent used, CCK-8 (1nM), CCh (1nM) or KCl (20mM), a micromolar concentration of pinaverium significantly inhibited contraction (88.36%, 93.10%, 93.92% inhibition respectively); this effect was concentration-dependent for CCh (IC50 = 0.73 +/- 0.08nM) and for CCK (IC50 = 0.92 +/- 0.12nM). In parallel, both nicardipine and diltiazem inhibit significantly contraction of isolated SMC. In inflamed colons, pinaverium (1 microM) display a significant higher efficacy than diltiazem or nicardipine to reduce cell contraction induced by CCK-8 or by KCl. In addition, RT-PCR experiments were performed to evidence tissue specificity of the L-type calcium channel. They revealed the expression of the messenger of the a-1 subunit L-type calcium channel (binding site of such CCBs), consistent with the expression of the rbC-2 splice variant of the alpha1-C gene. IN CONCLUSION: (i) the inhibition by calcium channel blockers of agonist-induced contractile activity suggest a modulation of SMC contraction upon extracellular calcium via 'L-type' voltage-dependent calcium channel; (ii) this study provides a rationale for the clinical use of pinaverium in colonic motor disoders affecting the contractility of SMC, since it appeared to decrease the contraction even in pathological situation; and (iii) RT-PCR experiments confirms the presence in human colon SMC of the alpha-1 subunit mRNA of calcium channel.

Adult↗
PubMed2001

Management of maternal Amanita phalloïdes poisoning during the first trimester of pregnancy: a case report and review of the literature.

BACKGROUND: Amanita phalloïdes poisoning produces acute liver failure and often death. Maternal poisonings are rare, and medical decisions of abortion or liver transplantation in this critical situation frequently are based on laboratory data. We report here the case of a 22-year-old-woman in the 11th week of pregnancy, who ingested mushrooms. CASE REPORT: The patient's clinical symptoms (e.g., vomiting and diarrhea) and blood chemistry data (persistent increases of aspartate aminotransferase and alanine aminotransferase and severe decreases in prothrombin, factor V, factor II, factor VII, and factor X) indicated poisoning of medium severity. The management consisted of intravenous hydration, and administration of silymarine and N-acetylcysteine. No fetal damage was observed, and birth and development of the infant (now 2 years of age) proceeded without incident. CONCLUSION: Abortion is not necessarily indicated in maternal poisoning by A. phalloïdes, even in the first trimester of pregnancy.

Adult↗
PubMed2000

Passive nitrate transport by root plasma membrane vesicles exhibits an acidic optimal pH like the H(+)-ATPase.

The net initial passive flux (J(Ni)) in reconstituted plasma membrane (PM) vesicles from maize (Zea mays) root cells was measured as recently described (P. Pouliquin, J.-P. Grouzis, R. Gibrat ¿1999 Biophys J 76: 360-373). J(Ni) in control liposomes responded to membrane potential or to NO(3)(-) as expected from the Goldman-Hodgkin-Katz diffusion theory. J(Ni) in reconstituted PM vesicles exhibited an additional component (J(Nif)), which was saturable (K(m) for NO(3)(-) approximately 3 mM, with J(Nifmax) corresponding to 60 x 10(-9) mol m(-2) s(-1) at the native PM level) and selective (NO(3)(-) = ClO(3)(-) > Br(-) > Cl(-) = NO(2)(-); relative fluxes at 5 mM: 1:0.34:0.19). J(Nif) was totally inhibited by La(3+) and the arginine reagent phenylglyoxal. J(Nif) was voltage dependent, with an optimum voltage at 105 mV at pH 6.5. The activation energy of J(Nif) was high (129 kJ mol(-1)), close to that of the H(+)-ATPase (155 kJ mol(-1)), and J(Nif) displayed the same acidic optimal pH (pH 6.5) as that of the H(+) pump. This is the first example, to our knowledge, of a secondary transport at the plant PM with such a feature. Several properties of the NO(3)(-) uniport seem poorly compatible with that reported for plant anion channels and to be attributable instead to a classical carrier. The physiological relevance of these findings is suggested.

Biological Transport↗
PubMed2000

CK-MB mass test in ischemic myocardial injury. Comparison of two tests: BioMerieux Vidas and sanofi access immunoassays.

The analytical and clinical performances of the new fluorescent immunoassay (CK-MB mass Vidas-BioMerieux) were examined and compared to the chemiluminescent test (CK-MB mass Access-Sanofi-Pasteur). Assay precisions of the CK-MB Vidas test within-assay or between-assay were less than 5.4 and 5.3%, respectively. Linearity was tested up to 214 microg/L. The CK-MB Vidas test was free of interference with CK-BB, CK-MM, and macro-CK. One hundred nineteen blood samples from patients with ischemic myocardial injury (IMI): acute myocardial infarction (AMI), suspected myocardial contusion (SMC), and unstable angina pectoris (UA), were tested using both immunoassays. In AMI, a good correlation was found (Y [CK-MB Access] = 1.1372 x [CK-MB Vidas] - 6.3902; r(2) = 0.96). In UA and SMC, low values were observed and both methods were well correlated (Y [CK-MB Access] = 1.3662 x [CK-MB Vidas] + 0.0671; r(2) = 0.97). Clinical data were in good agreement with both immunoassays. ROC analysis performed in AMI demonstrated that the clinical performances of the two assays were similar.

Adult↗
PubMed1999

The base substitution fidelity of HIV-1 reverse transcriptase on DNA and RNA templates probed with 8-oxo-deoxyguanosine triphosphate.

We have used 8-O-dGTP, a mutagenic nucleotide generated by oxidative metabolism, to probe the misincorporation potential of HIV-1 reverse transcriptase (RT) during DNA synthesis templated by the same nucleotide sequence as either RNA or DNA. With either template, 8-O-dGMP was misincorporated opposite template A, yielding characteristic A-->C transversions. The error rate with DNA was similar to that with RNA, suggesting that base misincorporation by the RT during first-strand and second-strand replication may contribute equally to the HIV-1 base substitution mutation rate. The rate of 8-O-dGMP misincorporation differed by more than 10-fold among the 20 adenines in the M13mp2 template where A-->C transversions can be detected. The transversion distribution was similar with the two templates, indicating that the effects of flanking nucleotides on misincorporation rates were similar. This is consistent with structural and biochemical data suggesting that HIV-1 RT binds RNA x DNA and DNA x DNA template-primers in the same orientation. The similarities in error rates and distribution further indicate that, despite differences in the structures of free RNA x DNA and DNA x DNA duplexes (e.g., minor groove dimensions), the polymerase active site that assembles upon substrate binding establishes a similar degree of nucleotide selectivity with both types of template-primers. Comparison of the RT error distribution to that observed with two Pol I family DNA polymerases and a Pol alpha family polymerase revealed common hot and cold spots for misincorporation. This suggests that the local nucleotide sequence influences the nucleotide selectivity of four polymerases in a similar manner, despite their differences in structure, biochemical properties, and functions.

Base Pair Mismatch↗
PubMed1999

Relative rates of insertion and deletion mutations in a microsatellite sequence in cultured cells.

A cell culture system has been used to determine the relative rates of insertions and deletions of integral numbers of dinucleotide repeats in a microsatellite sequence. A plasmid was constructed that contained 17 repeats of poly(dC-dA).poly(dG-dT) near the 5' end of a bacterial neomycin-resistance (neo) gene, such that the neo gene was translated in the (+1) reading frame. The plasmid was introduced into mismatch-repair-proficient and mismatch-repair-deficient mammalian cell lines. Rates of mutation to resistance to the neomycin analogue G418 were measured, and the nature of the mutations was determined. The mutations were all gains or losses of integral numbers of repeats, and mutations involving a single repeat greatly predominated over those involving multiple repeats. The data obtained from these studies were compared with results previously obtained with cells transfected with a similar plasmid in which the sequence of the oligonucleotide insert placed the neo gene in the (-1) reading frame. This experimental design made it possible to make direct comparisons between insertions and deletions of a single repeat unit. A significant excess of insertions over deletions was found in both repair-proficient and repair-deficient cell lines, although the few mutations involving more than two repeats were deletions.

Animals↗
PubMed1998

Calcitonin gene-related peptide-induced relaxation of isolated human colonic smooth muscle cells through different intracellular pathways.

Calcitonin gene-related peptide (CGRP) plays a significant role in the non-adrenergic non-cholinergic (NANC) regulation of intestinal tract motility. In this work, the contractile properties of enzymatically isolated circular smooth muscle cells (SMC) from human colon in response to CGRP were evaluated. Relaxation by CGRP (1 microM) was determined in cells maximally contracted by carbachol (CCh, 1 nM). Simultaneously, cGMP contents of SMC were measured by radioimmunoassay. CCh-induced contraction was inhibited by 1 microM CGRP (maximum: 69+/-5% within 60 sec); similarly, exposure of cells to sodium nitroprussiate (SNP), 1 microM, fully inhibited contraction (maximum: 89+/-8% within 30 sec). In the same time-course as for relaxation, CGRP and sodium nitroprussiate caused significant increase in intracellular cGMP levels (2- and 10-fold that of the basal level, respectively, P < 0.01). The nitric oxide synthase (NOS) inhibitor, L-N5(I-iminoethyl)ornithine, dihydrochloride, (L-NIO), 1 microM, partly inhibited SMC relaxation induced by CGRP (78.26%); the protein kinase inhibitor, N-(2-aminoethyl)-5-isoquinolinesulfonamide hydrochloride (H9), 1 microM, and the selective cAMP-dependent protein kinase inhibitor, adenosine-3',5'-monophosphorothioate triethylammonium salt, Rp isomer, (Rp-cAMP(S)), 1 microM, also caused inhibition of relaxation (70.30% and 28.6%, respectively). In parallel, the increase in cGMP caused by CGRP was partly reduced by L-NIO (65.47%) and by H9 (55%). In conclusion, the nitric oxide generation following exposure of human colonic SMC to sodium nitroprussiate causes relaxation through the cGMP pathway; on the other hand, exposure of SMC to CGRP causes relaxation in part by activation of nitric oxide synthase and guanylate cyclase and in part through the cAMP pathway.

Aged↗
PubMed1998

Stability of microsatellites in myeloid neoplasias.

Microsatellites are short, repeated DNA sequences that exist throughout the genome. Instability of these sequences, associated with defects in the DNA mismatch repair system, is the hallmark of hereditary non-polyposis colorectal cancer (HNPCC), and is also found in many sporadic cancers. Although many types of solid tumors exhibit this type of genetic instability, its involvement in hematologic cancers is less evident. We have investigated whether microstatellite instability (MSI) is involved in the transformation of myeloid cells to myelodysplastic syndrome (MDS) and/or acute myelogenous leukemia (AML). Both de novo and treatment-associated neoplasias were studied. Only one example of MSI was found in 48 patients, using a panel of 14 different microsatellite loci consisting of repeats of one to four base pairs. These results suggest that the genes responsible for MSI are not involved in the transformation of normal myeloid cells to MDS or AML.

Chromosome Aberrations↗
PubMed1998

Mutation rate of a microsatellite sequence in normal human fibroblasts.

Dinucleotide repeats, because of their repetitive nature, are prone to frameshift mutations, most likely via a DNA-polymerase slippage mechanism. Mutation rates in microsatellite DNA sequences are high in mismatch repair-defective cells. In normal cells, only estimates of maximal rates of mutation in microsatellites have been possible previously, because of the low sensitivity of screening assays for mutations in endogenous sequences. We have measured the spontaneous mutation rate of a dinucleotide repeat in diploid human foreskin fibroblasts. In our system, the mutation target is a (CA)17 repeat contained within a stably integrated plasmid. The repeat disrupts the reading frame of a neomycin (neo) resistance gene within the plasmid. Cells containing frameshift mutations in the CA repeat that correct the reading frame of the neo gene are selected using the neo analogue G418. This system of measuring microsatellite mutation rates is highly sensitive, because there is a specific target within which mutations can be selected. Fluctuation analysis of cells containing the target DNA yielded mutation rates of <3.1 x 10(-8) to 44.8 x 10(-8) mutations/cell/generation. This is the first report of a direct measurement of a spontaneous mutation rate of a microsatellite sequence in normal human cells.

Cells, Cultured↗
PubMed1998

Neurohormonal stimulation of histamine release from neuroendocrine cells of the human adenomatous prostate.

BACKGROUND: Neuroendocrine cells (NE) constitute a population of highly specialized cells in prostatic glands; histamine has never been described in these cells. This article shows the presence and the regulation of release of histamine in NE. METHODS: In 21 prostatic adenomas, NE were identified by specific antisera against neuroendocrine markers (chromogranin-A, synaptophysin), histamine, and histidine decarboxylase (HDC); a rate HDC-cDNA probe was used to detect this enzyme by in situ hybridization. RESULTS: Immunoreactive cells for chromogranin-A, histamine, and HDC were found among luminal epithelial glandular cells. Similar cells were also labeled with the HDC-cDNA probe. Glandular cells, isolated from prostatic adenomas, were shown to contain histamine (7-40 pmol/mg cellular protein). L(-) norepinephrine causes a time-dependent (t1/2 = 22 min) histamine release; the alpha 1-receptor antagonists WB-4101 and YM-617 specifically inhibited this release, in agreement with a mediation by alpha 1-adrenoreceptor subtype. CONCLUSIONS: There is some evidence for the presence in prostatic adenomas of histamine-forming cells of neuroendocrine type; histamine release from these cells is under the control of alpha 1-adrenoreceptor subtype.

Adrenergic alpha-Agonists↗
PubMed1998

p53 and follow-up of colorectal adenocarcinomas.

Circulating p53 antibodies (ELISA method), p53 genetic alterations (SSCP), and protein overexpression (immunohistochemistry) were studied in 41 patients with colorectal adenocarcinomas and 10 control patients. Carcinoembryonic antigen (CEA) and carbohydrate antigen 19.9 (CA 19-9) were evaluated in parallel. Ten patients with p53 antibodies and p53 overexpression were selected. Tumor DNA extracts from these 10 patients were analyzed by SSCP. Of all 41 patients, 10 (24%) showed significant levels of p53 antibodies, and p53 accumulation was detected in 20 (48%) patients. In six patients, p53 antibody concentrations decreased rapidly after surgery; in two patients, these levels returned to normal values. Of the 10 selected tumors, eight revealed TP53 gene mutations. Only two patients with high values of both CEA and CA 19-9 developed p53 antibodies. In conclusion, beside classical tumor markers, circulating p53 antibodies may be considered as additional markers for the management of patients with colorectal adenocarcinomas.

Adenocarcinoma↗
PubMed1997

Renovascular disease: Doppler ultrasound.

Color Doppler ultrasound (CDUS) seems to be an effective imaging technique for the diagnosis of renal vascular diseases. It is already the modality of choice for the detection of acute renal vein thrombosis and nonocclusive intrarenal vascular disorders including iatrogenic arteriovenous fistula and false aneurysm, particularly in patients with impaired renal function that precludes the use of iodinated contrast agents. Although proximal Doppler interrogation remains an important step in diagnosing renal artery (RA) stenosis, useful hemodynamic information can be obtained from the distal arterial bed. When CDUS fails in identifying proximal RAs, normal waveform velocity and morphology obtained from intrarenal arteries enable one to rule out RA occlusion and most of the severe stenoses (> or = 80%). Such information, which is not subject to a significant risk of technical failure, seems to be particularly useful in studying patients with acute renal failure of suspected vascular origin. Despite the extreme variability in reported performance between studies, CDUS has seemed to be a valuable tool compared with other noninvasive modalities in the diagnosis of RA stenosis. Whereas a CDUS-based strategy is already accepted in numerous specialized centers, a thorough evaluation of diagnostic criteria and extensive training of operators will allow CDUS to be widely accepted for the screening of patients at high risk for renovascular hypertension.

Humans↗
PubMed1997

Differential responsiveness to contractile agents of isolated smooth muscle cells from human colons as a function of age and inflammation.

To study the involvement of age and inflammation in motor colonic activity in man, contractile responses to CCK, carbachol, and KCl of isolated colonic smooth muscle cells (SMC) from normal and inflamed human colons were evaluated; the incidence of sex and smoking on contraction was also analyzed. Contractile responses to the three agonists were significantly lower in tissues with a low degree of inflammation than in tissues with high level of inflammation or normal tissues. This reduction in cell responsiveness appears to be nonspecific and nonreceptor mediated. A positive correlation of the contractile responses to the three stimulants with the age of patients was observed. In contrast, no association was found between sex, smoking, and cell contraction. In conclusion, contractions of SMC due to CCK, carbachol, and KCl were significantly modified during life; inflammation of the colon led to a loss of SMC responsiveness.

Adult↗