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Biomedical subjects

R J Turner

Publications and source records attributed to R J Turner.

At least 55 records · Page 3Linked to original sources
PubMed1999

Effect of haemorrhage on plasma propofol concentrations in a patient undergoing orthotopic liver transplantation.

We report a patient who underwent repeat orthotopic liver transplantation complicated by intraoperative blood loss of more than 59 litre. During liver transplantation, a constant rate propofol infusion was given and plasma samples were obtained throughout the procedure for propofol assay. Before the anhepatic phase of the procedure, plasma propofol concentrations reached a plateau at 1 microgram ml-1, and these concentrations were consistent with those predicted using a pharmacokinetic model. During the anhepatic phase of surgery, serum propofol concentrations increased progressively and exceeded those predicted by the pharmacokinetic model. Large intravascular fluid shifts associated with blood loss and subsequent blood replacement influenced plasma propofol concentrations observed in this patient.

Adult↗
PubMed1999

Characterization of a phosphorylation event resulting in upregulation of the salivary Na(+)-K(+)-2Cl(-) cotransporter.

Previous studies from our laboratory have shown a close correlation between increased Na(+)-K(+)-2Cl(-) cotransporter activity and increased cotransporter phosphorylation after beta-adrenergic stimulation of rat parotid acinar cells. We demonstrate here that these effects are paralleled by an increase in the number of high-affinity binding sites for the cotransporter inhibitor bumetanide in membranes prepared from stimulated acini. We also show that the sensitivity of cotransporter fluxes to inhibition by bumetanide is the same in both resting and isoproterenol-stimulated cells, consistent with the hypothesis that beta-adrenergic stimulation and the accompanying phosphorylation result in the activation of previously quiescent transporters rather than in a change in the properties of already active proteins. In addition, we demonstrate that the increased phosphorylation on the cotransporter resulting from beta-adrenergic stimulation is localized to a 30-kDa phosphopeptide obtained by cyanogen bromide digestion. Immunoprecipitation and Western blotting experiments demonstrate that this peptide is derived from the NH(2)-terminal cytosolic tail of the cotransporter, which surprisingly does not contain the sole protein kinase A consensus site on the molecule.

Adrenergic beta-Agonists↗
PubMed1999

Rapid changes in the coagulant proteins on saphenous vein endothelium in response to arterial flow.

Healthy endothelium provides a nonthrombogenic surface. In this study the authors investigated the effect of arterial flow on the saphenous vein endothelial expression of proteins controlling thrombosis. Human saphenous vein segments, freshly excised from patients, were placed in a validated in vitro circuit with flow conditions shown to simulate arterial or venous circulations. In separate experiments, placement of an external polytetrafluoroethylene (PTFE) stent was used to differentiate the effects of pulsatile wall deformation and shear stress, while addition of drugs to the vein perfusate allowed study of the role of ion channels in transducing the response of the vein to arterial flow. Endothelial concentrations of thrombomodulin, nitric oxide synthase, tissue factor, and tissue plasminogen activator were assessed by quantitative immunohistochemistry and Western blotting of endothelial cell lysates, in paired vein samples, in comparison to control proteins. Arterial flow conditions caused a rapid and significant reduction in the endothelial concentration of thrombomodulin: The immunostaining area decreased from 80.1 +/- 7.0 to 48.3 +/- 5.0 and 32.9 +/- 3.0% at 45 and 90 minutes respectively, p = 0.01. These findings were confirmed by Western blotting. The reduction in thrombomodulin concentration was unaffected by eliminating vein wall deformation by placement of an external PTFE stent or by including the K+ channel blocker tetraethylammonium (TEA) in the vein perfusate. In contrast, thrombomodulin concentrations remained high when blockers of stretch-activated cation and calcium channels were included in the vein perfusate. The endothelial concentration of nitric oxide synthase increased after 90 minutes of arterial flow and this change was abolished when TEA was included in the vein perfusate. Arterial flow induced rapid changes in saphenous vein antithrombotic proteins. Different cation channels mediated the flow-induced changes in thrombomodulin and nitric oxide synthase.

Blood Flow Velocity↗
PubMed1999

Gender, social status, and emotional reliance.

Past research has suggested the potential importance of considering emotional reliance, a dimension of interpersonal dependence, when addressing social and developmental risk factors for depression. Based on a probability sample of 1,393 adults aged 18-55 residing in Toronto, Canada, this paper addresses gender differences in emotional reliance and the relevance of emotional reliance in explaining the gender-depression association. We also explore link-ages between emotional reliance and status factors. Findings indicate that emotional reliance is significantly related to depression and that women report greater reliance than men, independent of social status factors like marital and parental status, education, income, and occupational prestige. Moreover, the positive association between emotional reliance and depression is greater for women. Several social status factors modify the relationship between gender and emotional reliance. Both education and occupational prestige reduce reliance, and are particularly beneficial in this regard for women. Marriage, on the other hand, increases emotional reliance, especially for men. We offer interpretations of this pattern of findings.

Adolescent↗
PubMed1999

The stress process and the social distribution of depression.

Mental health generally and depression in particular have been repeatedly shown to vary in relation to gender, socioeconomic status, marital status, and age. These status differences may be linked to mental health because they tend to define important differences in stress exposure and in the availability of coping resources. This paper examines the capacity of the stress-process model to account for the social distribution of depression. We employ mediation analyses using data from a 1990-1991 survey of Toronto community residents. In general, we found hypothesized risk factors to vary across these statuses with depressive symptoms and disorder and the distribution of protective factors to vary inversely. Results indicate that the model as expressed in our analyses accounts for a substantial minority of observed depression differences across individuals and for a considerable portion of reliably observed variation across social statuses. Our findings with respect to major depressive disorder parallel those for depressive symptomatology. Most compelling is the nearly total explanation of the socioeconomic status association with depressive symptoms and the substantial contribution toward explaining the socioeconomic status-disorder relationship when stress process mediators are accounted for.

Adolescent↗
PubMed1998

Genetic code origins: tRNAs older than their synthetases?

We present a phylogenetic analysis to determine whether a given tRNA molecule was established in evolution before its cognate aminoacyl-tRNA synthetase. The earlier appearance of tRNA versus their metabolically related enzymes is a prediction of the RNA world theory, but the available synthetase and tRNA sequences previously had not allowed a formal comparison of their relative time of appearance. Using data recently obtained from the emerging genome projects, our analysis points to the extant forms of lysyl-tRNA synthetase being preceded in evolution by the establishment of the identity of lysine tRNA.

Amino Acyl-tRNA Synthetases↗
PubMed1998

Molecular and topological characterization of the rat parotid Na+-K+-2Cl- cotransporter1.

Na+-K+-2Cl- cotransporters play a central role in driving salt and water movements across secretory and absorptive epithelia. We report the cloning of the rat parotid secretory Na+-K+-2Cl- cotransporter, rtNKCC1. The predicted amino acid sequence of this protein is highly homologous to a previously cloned NKCC1 from the shark rectal gland and to mammalian NKCC1s cloned from several cultured cell lines, confirming the presence of the NKCC1 isoform in a naturally occurring mammalian secretory epithelium. In contrast to previously published NKCC1 clones, our sequence also includes an apparently complete 2680 bp 3'-UTR. Hydropathy analyses of rtNKCC1 predicts that this protein consists of large hydrophilic N and C termini (approx. 30 kDa and 50 kDa, respectively) flanking a central hydrophobic transmembrane region consisting of ten to 12 membrane spanning domains. In addition, we report the results of confocal immunofluorescent microscopic studies using rat parotid acini and antibodies directed against specific regions of the predicted N- and C-terminal portions of rtNKCC1. These studies demonstrate that the epitopes recognized by these antibodies are exposed in permeabilized but not in unpermeabilized cells, indicating that the predicted N and C termini of rtNKCC1 are intracellular.

Amino Acid Sequence↗
PubMed1998

Human saphenous vein endothelial cells express a tetrodotoxin-resistant, voltage-gated sodium current.

Whole-cell patch-clamp electrophysiological investigation of endothelial cells cultured from human saphenous vein (HSVECs) has identified a voltage-gated Na+ current with a mean peak magnitude of -595 +/- 49 pA (n = 75). This current was inhibited by tetrodotoxin (TTX) in a concentration-dependent manner, with an IC50 value of 4.7 microM, suggesting that it was of the TTX-resistant subtype. An antibody directed against the highly conserved intracellular linker region between domains III and IV of known Na+ channel alpha-subunits was able to retard current inactivation when applied intracellularly. This antibody identified a 245-kDa protein from membrane lysates on Western blotting and positively immunolabeled both cultured HSVECs and intact venous endothelium. HSVECs were also shown by reverse transcription-polymerase chain reaction to contain transcripts of the hH1 sodium channel gene. The expression of Na+ channels by HSVECs was shown using electrophysiology and cell-based enzyme-linked immunosorbent assay to be dependent on the concentration and source of human serum. Together, these results suggest that TTX-resistant Na+ channels of the hH1 isoform are expressed in human saphenous vein endothelium and that the presence of these channels is controlled by a serum factor.

Adult↗
PubMed1998

Evidence for a physiological role of NH4+ transport on the secretory Na(+)-K(+)-2Cl- cotransporter.

The secretory Na(+)-K(+)-2Cl- cotransporter in salivary acinar cells is responsible for driving the transepithelial Cl- fluxes that give rise to fluid secretion. We demonstrate that the application of the muscarinic agonist carbachol to rat parotid acini results in an intracellular acid load that can be blocked by bumetanide, a specific inhibitor of the cotransporter. One component of this bumetanide-sensitive acid load is ouabain-sensitive while a second is dependent on the presence of sub-millimolar concentrations of NH4+ in our media. Our data indicate that this latter effect arises from NH4+ entry on the cotransporter operating in a Na(+)-NH4(+)-2Cl- cotransport mode and that at physiological NH4+ levels in the rat (approximately 0.1 mM), 10-15% of the acinar Cl- entry occurs via this route. We suggest that Na(+)-NH4(+)-2Cl- cotransport may also play a significant physiological role in other cell types and that this mode of operation of the secretory Na(+)-K(+)-2Cl- cotransporter could account for the currently unexplained presence of this protein in a number of tissues.

Ammonia↗
PubMed1998

A novel and ubiquitous system for membrane targeting and secretion of cofactor-containing proteins.

We report the identification of the proteins encoded by the mttABC operon (formerly yigTUW), which mediate a novel Sec-independent membrane targeting and translocation system in Escherichia coli that interacts with cofactor-containing redox proteins having a S/TRRXFLK "twin arginine" leader motif. A pleiotropic-negative mutant in mttA prevents the periplasmic localization of twin arginine redox enzymes, including nitrate reductase (NapA) and trimethylamine N-oxide reductase (TorA). The mutation also prevents the correct localization of the integral membrane molybdoenzyme dimethylsulfoxide reductase (DmsABC). The DmsA subunit has a twin arginine leader. Proteins with a Sec-dependent leader or which assemble spontaneously in the membrane are not affected by this mutation. MttA, B, and C are members of a large family of related sequences extending from archaebacteria to higher eukaryotes.

2S Albumins, Plant↗
PubMed1998

Adaptation of an enzyme to regulatory function: structure of Bacillus subtilis PyrR, a pyr RNA-binding attenuation protein and uracil phosphoribosyltransferase.

BACKGROUND: The expression of pyrimidine nucleotide biosynthetic (pyr) genes in Bacillus subtilis is regulated by transcriptional attenuation. The PyrR attenuation protein binds to specific sites in pyr mRNA, allowing the formation of downstream terminator structures. UMP and 5-phosphoribosyl-1-pyrophosphate (PRPP), a nucleotide metabolite, are co-regulators with PyrR. The smallest RNA shown to bind tightly to PyrR is a 28-30 nucleotide stem-loop that contains a purine-rich bulge and a putative-GNRA tetraloop. PyrR is also a uracil phosphoribosyltransferase (UPRTase), although the relationship between enzymatic activity and RNA recognition is unclear, and the UPRTase activity of PyrR is not physiologically significant in B. subtilis. Elucidating the role of PyrR structural motifs in UMP-dependent RNA binding is an important step towards understanding the mechanism of pyr transcriptional attenuation. RESULTS: The 1.6 A crystal structure of B. subtilis PyrR has been determined by multiwavelength anomalous diffraction, using a Sm co-crystal. As expected, the structure of PyrR is homologous to those proteins of the large type I PRTase structural family; it is most similar to hypoxanthine-guanine-xanthine PRTase (HGXPRTase). The PyrR dimer differs from other PRTase dimers, suggesting it may have evolved specifically for RNA binding. A large, basic, surface at the dimer interface is an obvious RNA-binding site and uracil specificity is probably provided by hydrogen bonds from mainchain and sidechain atoms in the hood subdomain. These models of RNA and UMP binding are consistent with biological data. CONCLUSIONS: The B. subtilis protein PyrR has adapted the substrate- and product-binding capacities of a PRTase, probably an HGXPRTase, producing a new regulatory function in which the substrate and product are co-regulators of transcription termination. The structure is consistent with the idea that PyrR regulatory function is independent of catalytic activity, which is likely to be extremely low under physiological conditions.

Amino Acid Sequence↗
PubMed1998

Increased expression of the secretory Na+-K+-2Cl- cotransporter with differentiation of a human intestinal cell line.

We studied the expression of the secretory Na(+)-K(+)- 2Cl- cotransporter during epithelial differentiation using the clonal human adenocarcinoma cell line HT29-18. Differentiation of HT29-18 cells was accompanied by up to 7-fold increases in cotransporter protein levels, approximately 3-fold increases in cotransporter mRNA levels, and approximately 2.5-fold increases in cotransporter functional expression. No apparent change in cotransporter mRNA stability was observed with differentiation, suggesting that these effects may be due to differences in mRNA transcription rate. Confocal immunofluorescence microscopy showed that undifferentiated cells grew in multilayers and exhibited a diffuse, apparently unlocalized membrane labeling by anti-Na(+)-K(+)-2Cl- cotransporter antibody. In contrast, differentiated cells grew in monolayers with strong cotransporter labeling localized to the basal and lateral membranes. Taken together with previous studies demonstrating that expression of the cystic fibrosis transmembrane regulator is also increased following HT29-18 cell differentiation, our results suggest that these cells provide a promising model for studying epithelial differentiation to a Cl- secretory phenotype.

Adenocarcinoma↗
PubMed1998

Purification and characterization of Bacillus subtilis PyrR, a bifunctional pyr mRNA-binding attenuation protein/uracil phosphoribosyltransferase.

Bacillus subtilis PyrR has been shown to mediate transcriptional attenuation at three separate sites within the pyrimidine nucleotide biosynthetic (pyr) operon. Molecular genetic evidence suggests that regulation is achieved by PyrR binding to pyr mRNA. PyrR is also a uracil phosphoribosyltransferase (UPRTase). Recombinant PyrR was expressed in Escherichia coli, purified to homogeneity, physically and chemically characterized, and examined with respect to both of these activities. Mass spectroscopic characterization of PyrR demonstrated a monomeric mass of 20,263 Da. Gel filtration chromatography showed the native mass of PyrR to be dependent on protein concentration and suggested a rapid equilibrium between dimeric and hexameric forms. The UPRTase activity of PyrR has a pH optimum of 8.2. The Km value for uracil is very pH-dependent; the Km for uracil at pH 7.7 is 990 +/- 114 muM, which is much higher than for most UPRTases and may account for the low physiological activity of PyrR as a UPRTase. Using an electrophoretic mobility shift assay, PyrR was shown to bind pyr RNA that includes sequences from its predicted binding site in the second attenuator region. Binding of PyrR to pyr RNA was specific and UMP-dependent with apparent Kd values of 10 and 220 nM in the presence and absence of UMP, respectively. The concentration of UMP required for half-maximal stimulation of binding of PyrR to RNA was 6 muM. The results support a model for the regulation of pyr transcription whereby termination is governed by the UMP-dependent binding of PyrR to pyr RNA and provide purified and characterized PyrR for detailed biochemical studies of RNA binding and transcriptional attenuation.

Bacillus subtilis↗
PubMed1998

Selenium metabolism in Escherichia coli.

Escherichia coli will reduce selenite (SeO3(2-)) and selenate (SeO4(2-)) to elemental selenium Se0. Selenium will also become incorporated into proteins as part of the amino acids selenocysteine or selenomethionine. The reaction of selenite with glutathione produces selenodiglutathione (GS-Se-GS). Selenodiglutathione and its subsequent reduction to glutathioselenol (GS-SeH) are likely the key intermediates in the possible metabolic fates of selenium. This review presents the possible pathways involving selenium in E. coli. Identification of intermediates and potential processes from uptake of the toxic oxyanions through to their detoxification will assist us in understanding the complexities of metalloid oxyanion metabolism in these bacteria.

Escherichia coli↗
PubMed1998

Acute infiltration by non-Hodgkin's B-cell lymphoma of lesions of disseminated herpes zoster.

A man with a 15-year history of non-Hodgkin's lymphoma presented with disseminated herpes zoster which initially responded to aciclovir. This was shortly followed by an acute exacerbation in the sites previously affected which was apparently resistant to antiviral therapy. Biopsy revealed a dense monomorphic lymphocytic infiltrate below active herpes zoster which had the same morphology and immunoreactivity as the underlying lymphoma. His clinical condition resolved with further chemotherapy for his lymphoma and continued treatment with aciclovir.

Herpes Zoster↗
PubMed1998

Administration of a crystalloid fluid preload does not prevent the decrease in arterial blood pressure after induction of anaesthesia with propofol and fentanyl.

Anaesthesia was induced in 58 women (ASA I or II) undergoing elective gynaecological procedures, using propofol 2.5 mg kg-1 and fentanyl 1.5 micrograms kg-1. Patients were allocated to receive 20 ml kg-1 of crystalloid fluid preload over 20 min or to receive no fluids before induction of anaesthesia. A significant decrease in systolic arterial pressure (< 75% of baseline value) occurred in both the fluid-loaded and the control groups, and was similar in both groups. Administration of a fluid preload did not attenuate the decrease in systolic arterial pressure after induction of anaesthesia with propofol and fentanyl.

Adult↗