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Biomedical subjects

A Chollet

Publications and source records attributed to A Chollet.

At least 37 records · Page 2Linked to original sources
PubMed1995

Ten-year experience with a basic technical skills and perioperative management workshop for first-year residents.

Teaching technical skills is one of the most crucial tasks of the academic surgeon. The 10-year experience with a psychomotor skills laboratory at the Department of Surgery of the Université de Montréal is reported. Since 1983, first-year trainees were freed of hospital duties for "a week of surgical techniques" to develop their basic surgical technique and perioperative skills. Cognitive and practical sessions were designed for two groups of 10 residents. Teaching videos, suture boards, biologic substitutes, animal laboratory, round table discussions and formal lectures were the techniques used. Cognitive sessions were designed to provide information on instrumentation, adequate preoperative preparation, general organization of the operating room, intensive care and endoscopy units. The surgical procedures were approved by the local animal ethics committee. The program helped residents achieve surgical dexterity in a less stressful and more controlled manner than in the operating room. Close relationships of the trainees with their peers and teachers were established early helped to improve the operating environment. This program helps junior residents understand the complex world of the operating room and reduces the operative risks related to technique.

Animals↗
PubMed1994

Palmitoylation but not the extreme amino-terminus of Gq alpha is required for coupling to the NK2 receptor.

Gq alpha and G11 alpha differ from other G protein alpha subunits in that they have unique, conserved 6 residue amino-terminal extensions. Wild-type and amino-terminal mutants of Gq alpha expressed in COS cells were analyzed for their ability to functionally couple with co-expressed neurokinin NK2 receptor. Wild-type, T2A and delta 2-7 Gq alpha were able to stimulate agonist driven phospholipase C (PLC) activity in identical manners. Other activities of these two amino-terminal mutants including aluminum fluoride stimulated PLC activity, palmitoylation, interaction with G beta gamma subunits and GTP gamma S-induced trypsin resistance are also similar to the wild-type alpha subunit. This demonstrates that the NK2 receptor is able to functionally interact with the alpha subunit of Gq and that the first seven amino-acids of Gq alpha are not required for any of the alpha subunit functions tested. In contrast to the T2A and delta 2-7 mutants, a C9,10A Gq alpha mutant was not able to couple to either the NK2 receptor or PLC, as assessed by high-affinity agonist binding and activation of PLC either in intact cells or in vitro. The C9,10A protein was able to assume a GTP gamma S-induced trypsin-resistant conformation and partitioned primarily to the pelletable fraction in a manner similar to the wild-type protein. However, it was not labeled with [3H]palmitic acid. This suggests that blocking palmitoylation at the amino-terminus of Gq alpha results in a loss of functional activity which reflects an inability to interact with both the receptor and downstream signaling targets.

Aluminum Compounds↗
PubMed1994

Conformational properties of four peptides corresponding to alpha-helical regions of Rhodospirillum cytochrome c2 and bovine calcium binding protein.

Four peptides corresponding to alpha-helical regions delimited by residues 63-73 and 97-112 of cytochrome c2 (Rhodospirillum) and residues 24-36 and 45-55 of bovine calcium binding protein are predicted to be alpha-helical by a recently developed method [Rooman, M., Kocher, J.P., & Wodak, S.J. (1991) J. Mol. Biol. 221, 961-979], synthesized by solid phase methods, and purified by HPLC, and their solution conformations are determined by NMR and CD. The observed conformational properties of these peptides in solution confirmed prediction results: in water/TFE (60/40, v/v) at room temperature, these peptides adopt an alpha-helical conformation, as shown by an extended pattern of strong, sequential dNN(i,i + 1) NOE cross-peaks, d alpha N(i,i + 1) NOEs of reduced intensity, several medium-range [d alpha N(i,i + 3), d alpha N(i,i + 4), d alpha beta-(i,i + 3)] NOE connectivities, small 3JH alpha N values, and more upfield alpha-proton chemical shifts. CD studies at different TFE concentrations and at room temperature provide further evidence of the propensity of these peptides to adopt an alpha-helical conformation in solution, as determined by the ellipticity values at 222 nm, and by deconvolution of the CD spectra. According to the method used, helicities in the range 34-50% and 55-75% are found for the 63-73 and 97-112 fragments of cytochrome c2, respectively, and in the range 53-80% and 42-65% for the fragments 24-36 and 45-55 of calcium binding protein in water/TFE (60/40, v/v) at 298 K. In addition, the experiments and predictions agree for those residues that are more flexible. Finally, the relevance of our results for the protein folding pathways is discussed.

Algorithms↗
PubMed1994

Synthesis and characterization of selective fluorescent ligands for the neurokinin NK2 receptor.

Several fluorescent probes for the NK2 receptor were designed, synthesized, and pharmacologically characterized. These fluorescent ligands are analogues of the selective NK2 heptapeptide antagonist N-alpha-benzoyl-Ala-Ala-D-Trp-Phe-D-Pro-Pro-Nle-NH2 (1, GR94800). They were obtained by substitution of 2,n-diaminoalkyl amino acid (n = 3-6) for Ala1 and the subsequent coupling of the fluorophore NBD (7-nitrobenz-2-oxa-1,3-diazol-4-yl) or fluoresceinthiocarbamyl to the N-omega amino group. The fluorescent derivatives retained high binding affinities for the NK2 receptor in transfected CHO cells. In contrast, fluorescent derivatives made by replacing the N-alpha-benzoyl group of 1 by NBD or fluorescein were considerably less active. The effect on ligand potency of varying the length of the spacer arm between the peptide moiety and the fluorescent group was also studied. The most potent fluorescent antagonists were N-alpha-benzoyl-Dab(gamma-NBD)-Ala-D-Trp-Phe-D-Pro-Pro-Nle-NH2 (5B), pKi = 8.87 for NK2; N-alpha-benzoyl-Orn (delta-NBD)-Ala-D-Trp-Phe- D-Pro-Pro-Nle-NH2 (4B), pKi = 8.84; and N-alpha-benzoyl-Lys(epsilon-NBD)-Ala-D-Trp-Phe-D-Pro-Pro-Nle-NH2 (3B), pKi = 8.83. These three compounds were highly selective for NK2 over NK3 and NK1 receptors. We show that these fluorescent ligands are useful tools for the detection of NK2 receptor expression by flow cytometry. Additionally, these fluorescent probes should prove valuable for fluorescence microscopy and study of ligand-receptor interaction by spectrofluorimetry.

Amino Acid Sequence↗
PubMed1994

Calcium influx and protein kinase C alpha activation mediate arachidonic acid mobilization by the human NK-2 receptor expressed in Chinese hamster ovary cells.

We have cloned a cDNA encoding the human ileal neurokinin-2 (NK-2) receptor which mediates powerful neurokinin A-stimulated arachidonic acid (AA) and prostaglandin release when expressed in CHO cells. Two major signal transduction events appear to underlie this response. Firstly, AA liberation is critically dependent upon agonist-stimulated influx of extracellular Ca2+ although not release from intracellular stores. Secondly, NK-2 receptor-linked AA mobilization requires concomitant PKC activation and based upon limited subtype immunodetectability as well as toxin, identical pretreatment inhibits AA release partially and blocks PKC alpha translocation completely. These observations indicate that in this cell system AA liberation reflects NK-2 receptor-dependent activation of two distinct but converging signal transduction pathways regulated by different G-protein species and involving Ca2+ influx and PKC alpha activation.

Animals↗
PubMed1993

Expression and characterization of human D4 dopamine receptors in baculovirus-infected insect cells.

The human D4 dopamine receptor has been genetically engineered for expression in insect cells using the baculovirus system. A D4 cDNA gene fusion construct [(1991) Nature 350, 610-614] was synthetically modified to remove two introns from the coding region, and expressed in S. frugiperda (Sf9) cells as a fusion with a short sequence from the polyhedrin protein. Binding assays with [3H]spiperone indicated high levels of D4 receptor binding 90 h after infection and a pharmacological profile identical to that reported for D4 receptors expressed in COS-7 cells using the cDNA gene hybrid. We also show that the agonist binding affinity of D4 receptors expressed in Sf9 cells can be shifted by GTP-gamma-S, indicating coupling to G-proteins.

Animals↗
PubMed1993

Biochemical characterization and solubilization of human NK2 receptor expressed in Chinese hamster ovary cells.

The human ileum neurokinin NK2 receptor has been stably expressed in Chinese hamster ovary (CHO) cells using the dihydrofolate reductase (DHFR) expression system. Amplified cell populations expressing approximately 7 x 10(5) NK2 receptors/cell were selected in the presence of the DHFR inhibitor methotrexate. Cross-linking of [125I]NKA to NK2 receptor transfected cells revealed a specifically labeled protein of apparent molecular weight 64 kDa by SDS-polyacrylamide gel electrophoresis. This protein was deglycosylated by the enzymes N-glycosidase F and endoglycosydase F to a protein of apparent molecular weight of 39 kDa. The NK2 receptor was solubilized in an active form from CHO cell membranes using the zwitterionic detergent CHAPS. This method represents a valuable approach for the production of significant amounts of NK2 receptor protein from mammalian cells.

Amino Acid Sequence↗
PubMed1991

Comparative NMR analysis of the decadeoxynucleotide d-(GCATTAATGC)2 and an analogue containing 2-aminoadenine.

The dodecadeoxynucleotide duplex d-(GCATTAATGC)2 has been prepared with all adenine bases replaced by 2-NH2-adenine. This modified duplex has been characterized by nuclear magnetic resonance (NMR) spectroscopy. Complete sequence-specific 1H resonance assignments have been obtained by using a variety of 2D NMR methods. Multiple quantum-filtered and multiple quantum experiments have been used to completely assign all sugar ring protons, including 5'H and 5'H resonances. The assignments form the basis for a detailed comparative analysis of the 1H NMR parameters of the modified and parent duplex. The structural features of both decamer duplexes in solution are characteristic of the B-DNA family. The spin-spin coupling constants in the sugar rings and the relative spatial proximities of protons in the bases and sugars (as determined from the comparison of corresponding nuclear Overhauser effects) are virtually identical in the parent and modified duplexes. Thus, substitution by this adenine analogue in oligonucleotides appears not to disturb the global or local conformation of the DNA duplex.

2-Aminopurine↗
PubMed1991

Periosteal suspension of the lower eyelid and cheek following subciliary exposure of facial fractures.

Following craniofacial procedures that involve stripping of the periosteum and soft tissue over the zygomatic maxillary complex, descent of soft tissue with a decrease in anterior projection over the malar area and increase in fullness in the nasolabial fold have been seen to be a problem by these authors. Simple repositioning of the soft tissues to their normal anatomic position may be used to alleviate this problem.

Cheek↗
PubMed1990

Preparation, application and biological characterization of interleukin-1 beta mutant protein biotinylated at a single site.

Selective biotinylation of human interleukin-1 beta was achieved by reaction of an interleukin-1 beta mutant protein containing a surface-accessible cysteine with maleimido-biotin. A defined interleukin-1 beta derivative biotinylated at a single site was obtained. This compound retained full affinity for both the interleukin-1 receptor and streptavidin or avidin; however, its biological activity was significantly reduced in proliferative assays. Biotinylated interleukin-1 beta mutant protein bound to fluorescein-labelled avidin was used in flow cytometric analysis of interleukin-1 receptors. Internalization of the complex between biotinylated interleukin-1 beta mutant protein and streptavidin in a murine thymoma cell line was demonstrated.

Animals↗
PubMed1988

Thermodynamic studies of base pairing involving 2,6-diaminopurine.

The thermal stabilities of oligodeoxyribonucleotide duplexes containing 2,6-diaminopurine (D) matched with each of the four normal DNA bases were determined by optical melting techniques. Comparison of optical melting curves yielded relative stabilities for the D-containing standard base pairs in an otherwise identical base-pair sequence. The D:T pair was found to be more stable than the A:T pair in dC3DG3:dC3TG3, as stable as the A:T in dCT3DT3G:dCA3TA3G, and less stable than the A:T in dCA3DA3G:dCT7G. The order of stabilities for X:Y in the DNA duplex dCA3XA3G:dCT3YT3G is: (A:T) greater than (T:D) congruent to (D:T) greater than or equal to (T:A) greater than (C:D) congruent to (D:A) congruent to (D:G) greater than or equal to (D:C) congruent to (G:D) congruent to (D:D) greater than or equal to (A:D). Implications of these results for design of DNA oligonucleotide probes are discussed.

2-Aminopurine↗
PubMed1988

Biological characterization of human interleukin-2 mutant proteins. Structure-activity relationship studies.

Several human interleukin-2 (IL-2) mutant proteins have been produced previously by site-directed mutagenesis and found to have different capacities to induce T-cell proliferative activity. In this study, the abilities of these IL-2 mutant proteins to activate natural killer cells and to induce interferon-gamma production have been evaluated, and the binding of these proteins to IL-2 receptors analyzed. Natural killer cell activation and interferon-gamma induction assays showed that the relative activities of IL-2 mutant proteins were consistent with their relative activities in T-cell proliferation assay. Receptor-binding studies showed that the activities of most proteins correlated well with their respective affinities for high-affinity IL-2 receptors on CTLL-2 cells. Interestingly, although the mutant protein with deletion of cysteine 125 (des-Cys125) was biologically less active than the protein with substitution of alanine for cysteine 105 (Ala105), both proteins exhibited similar affinity. Des-Cys125, like IL-2 and Ala105, also caused down-regulation of high-affinity IL-2 receptors. Binding studies on MLA-144, a cell line expressing mainly intermediate-affinity IL-2 receptors (IL-2R beta), however, showed that des-Cys125 had much lower affinity than Ala105. These results suggest that binding of IL-2 and mutant proteins to the IL-2R beta component of the high-affinity receptor is essential for the induction of biological effects.

Animals↗
PubMed1988

DNA containing the base analogue 2-aminoadenine: preparation, use as hybridization probes and cleavage by restriction endonucleases.

The base analogue 2-aminoadenine (2,6-diaminopurine, D) has been introduced at selected positions into synthetic oligodeoxyribonucleotides and DNA by the combined use of chemical and enzymatic methods. 2-aminoadenine substitution for adenine introduces changes in the minor groove of DNA and creates an additional hydrogen bond in the Watson-Crick base pair with thymine. Oligonucleotide hybridization probes containing 2-aminoadenine showed increased selectivity and hybridization strength during DNA-DNA hybridization to phage or genomic target DNA. Properties of the base analogue with respect to DNA modifying enzymes were examined. 2-aminoadenine was used to probe minor groove determinants during the treatment of DNA by 12 restriction endonucleases. Inhibition of cleavage was found for several restriction enzymes.

2-Aminopurine↗
PubMed1985

Molecular cloning of mouse tumour necrosis factor cDNA and its eukaryotic expression.

Tumour necrosis factor (TNF), released by induced macrophages, causes tumour necrosis in animals and kills preferentially transformed cells in vitro. mRNA induced in the established mouse monocytic PU 5.1.8 cell line by lipopolysaccharide, was converted into double-stranded cDNA and cloned in the pAT153 vector. Recombinant plasmids were screened by plus-minus hybridization and TNF-specific oligonucleotide probes constructed on the basis of partial amino acid sequences of rabbit TNF. A series of TNF specific clones were identified and confirmed by hybrid selection of mouse TNF-specific mRNA. The sequence codes for a 235 amino acids long polypeptide, of which 156 amino acids presumably correspond to the mature product. It can be concluded that mature mouse TNF is a glycosylated dimer. Biologically active TNF was secreted by both Cos-I and CHO-cells transfected with the chimaeric expression vector pSV2d2-mTNF containing the coding region of the mouse TNF cDNA gene.

Amino Acid Sequence↗
PubMed1985

Optimizing the expression in E. coli of a synthetic gene encoding somatomedin-C (IGF-I).

Double-stranded DNA encoding the human hormone somatomedin-C (SMC) has been synthesized. This synthetic gene has been inserted into a plasmid bearing the strong leftward promoter (PL) of bacteriophage lambda and expressed in E. coli. Codons for the N-terminal region of SMC which maximized the hormone's synthesis were chosen in an SMC-lac z fusion assay. The amounts of SMC accumulated in E. coli were influenced by mutations at two chromosomal loci, lon and htpR.

ATP-Dependent Proteases↗
PubMed1985

Biotin-labeled synthetic oligodeoxyribonucleotides: chemical synthesis and uses as hybridization probes.

Oligodeoxynucleotides have been selectively labeled with biotin at their 5'-termini through an aminoalkylphosphoramide linker arm by an efficient chemical method. The reactions were performed in aqueous solution on unprotected oligonucleotides and were insensitive of the sequence and length of the oligonucleotide. 5'-biotin-labeled oligonucleotides were hybridized to dot, Southern and genomic blots of target plasmid DNA immobilized on nitrocellulose filters. Detection level is about 2 fmole. There is no noticeable disturbance of the strength and selectivity of hybridization of the 5'-biotin-labeled probes in comparison with non-modified DNA.

Base Sequence↗
PubMed1985

[Fatal hypoxemia following extracorporeal circulation for aortocoronary bypass. A case].

A lethal case of acute respiratory distress syndrome of the adult following extracorporeal circulation for aorto-coronary bypass is reported. This case illustrates the two mechanisms currently thought to be responsible for this pathology: (1) the passage of blood over the synthetic fibres of the cardiopulmonary bypass machine activates the complement, and the systemic inflammatory reaction that ensues accounts for the increased permeability of the alveolar capillary membrane; (2) the haemodilution inherent in extracorporeal circulation explains the hypoproteinaemia usually observed at the end of the procedure; the resulting fall in capillary osmotic pressure upsets the equilibrium of pressures in the capillary vessels.

Coronary Artery Bypass↗