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K Barnes

Publications and source records attributed to K Barnes.

At least 55 records · Page 3Linked to original sources
PubMed1997

The endothelin system and endothelin-converting enzyme in the brain: molecular and cellular studies.

The biologically active vasoactive peptides, the endothelins (ETs), are generated from inactive intermediates, the big endothelins, by a unique processing event catalysed by the zinc metalloprotease, endothelin converting enzyme (ECE). In this overview we examine the actions of endothelins in the brain, and focus on the structure and cellular locations of ECE. The heterogeneous distribution in the brain of ET-1, ET-2, and ET-3 is discussed in relation to their hemodynamic, mitogenic and proliferative properties as well as their possible roles as neurotransmitters. The cellular and subcellular localization of ECE in neuronal and in glial cells is compared with that of other brain membrane metalloproteases, neutral endopeptidase-24.11 (neprilysin), angiotensin converting enzyme and aminopeptidase N, which all function in neuropeptide processing and metabolism Unlike these ectoenzymes, ECE exhibits a dual localisation in the cell, being present on the plasma membrane and also, in some instances, being concentrated in a perinuclear region. This differential localization may reflect distinct targeting of different ECE isoforms, ECE-1 alpha, ECE-1 beta, and ECE-2.

Animals↗
PubMed1997

Expression of endothelin-converting enzyme in both neuroblastoma and glial cell lines and its localization in rat hippocampus.

Endothelin-converting enzyme is a phosphoramidon-sensitive metalloprotease that cleaves big endothelin to the potent vasoconstrictor peptide, endothelin. The converting enzyme is expressed in endothelial cells in a variety of tissues and in some secretory cells. In the present study, phosphoramidon-sensitive endothelin-converting enzyme activity has been demonstrated by radioimmunoassay in the neuroblastoma cell line, SH-SY5Y, and in Bu17 and C6 glioma lines. The identity of the activity was confirmed by immunoblotting, revealing a polypeptide of approximately 120 kDa in each of these lines, in D384 glioma cells, and in primary astrocytes. Immunofluorescence revealed the cell-surface location of endothelin-converting enzyme in the neuronal and glial cell lines and in primary astrocytes. Pretreatment of SH-SY5Y and Bu17 cells with phosphoramidon resulted in an apparent concentration of the enzyme protein in an intracellular compartment. Immunoperoxidase-staining of rat brain sections located this metalloprotease to the pyramidal cells of the hippocampus. Endothelin-converting enzyme-1 was revealed by in situ hybridisation in the neuronal and glial cell lines.

Animals↗
PubMed1997

Is kidney length a good predictor of kidney volume?

Kidney length is commonly used to determine kidney size; however, its relationship to kidney volume is not well established. This study evaluated the association between kidney length and kidney volume. Eighteen healthy adults (9 men and 9 women) consented to take part in this prospective study; all 18 underwent spiral computerized tomography (CT) of the kidneys, 14 of 18 also underwent kidney ultrasound. Kidney volume was measured by totaling the areas of the CT scan cuts, and kidney length was measured both on the kidney ultrasound and on the CT scan. Each independent variable, CT length (CTL) and ultrasound length (USL), was regressed against the dependent variable, kidney volume. Kidney length explained only 10% of the variability of the volume, although length x width was a better predictor of kidney volume (r = 0.72, P < 0.001). It was concluded that kidney length does not reliably predict kidney volume and that other methods, both clinical and radiologic, should be considered when a more exact determination of renal volume is clinically relevant.

Adult↗
PubMed1996

Metallopeptidase inhibitors induce an up-regulation of endothelin-converting enzyme levels and its redistribution from the plasma membrane to an intracellular compartment.

Endothelin-converting enzyme is a phosphoramidon-sensitive membrane metallopeptidase that catalyses the final step in biosynthesis of the potent vasoactive endothelin peptides. Immunomagnetic separation technology and immunohistochemistry have been used to demonstrate the co-localisation of endothelin-converting enzyme with the established ectoenzyme, aminopeptidase N, on the surface of endothelial cells. Unlike aminopeptidase N, however, endothelin-converting enzyme is seen to associate in clusters on the plasma membrane which can be distinguished from caveolae both biochemically and immunologically. Pre-treatment of endothelial cells with the metallopeptidase inhibitors phosphoramidon or thiorphan in the range 0.01-100 microM produced a dose-dependent increase in the levels of endothelin-converting enzyme protein and its accumulation in an intracellular compartment. No corresponding change in the levels of endothelin-converting enzyme-1 mRNA was detected under these conditions, nor in the levels of the closely related metalloenzyme, endopeptidase-24.11. The phosphoramidon and thiorphan-dependent increase is not due to direct inhibition of endothelin-converting enzyme not endopeptidase-24.11 but, rather, to an inhibition of the selective turnover of endothelin-converting enzyme protein.

Animals↗
PubMed1996

Olfaction and prey search in the carnivorous leech Haemopis marmorata

Haemopis marmorata, the green horse leech, is carnivorous and readily eats earthworms. Using a Y-maze with flowing water, we show that specimens of H. marmorata are attracted to live earthworms. Ablating the dorsal lip, the presumed site of the chemoreceptors that this species uses in prey search, disrupts the ability of the leeches to find the earthworms in the Y-maze. Earthworm wash, a preparation of the collagen coating of earthworm skin, shock-induced earthworm secretion, mammalian blood and a salt&shy;arginine mixture are not attractive to the green horse leech. The tails of freshly killed earthworms are attractive to the leeches, but tails from worms killed 8&shy;12 h previously and stored cold are not. Our conclusion is that the earthworms produce a metabolite that attracts the leeches.

Journal Article↗
PubMed1995

Localization of rat endothelin-converting enzyme to vascular endothelial cells and some secretory cells.

Endothelin is a potent vasoconstrictive peptide that is produced by vascular endothelial cells; it is formed from its precursor, big endothelin, by endothelin-converting enzyme (ECE). In this work, ECE was studied using specific monoclonal antibodies. In immunoblotting, ECE was estimated to be a 300 kDa protein on SDS/PAGE under non-reducing conditions, and 130 kDa under reducing conditions. Cross-linking experiments revealed that ECE is composed of two disulphide-linked subunits. Localization of ECE was studied at the cellular and subcellular levels in various rat tissues and cells. High-level expression of ECE was observed in membrane fractions of simian virus 40-transformed rat endothelial cells by immunoblotting, but the immunoreactive band was absent form aortic smooth muscle cells and cytosolic fractions of endothelial cells. In immunohistochemical analysis, ECE was found to be localized in the endothelial cells of the aorta, lung, kidney, liver and heart. Confocal immunofluorescent microscopy showed that most of the ECE in endothelial cells and cells transfected with ECE cDNA was clustered along the plasma membrane. Intact COS or CHO cells transfected with ECE cDNA rapidly and efficiently cleaved big endothelin-1 added to the culture medium. Thus endothelial cells express ECE on the plasma membrane and the active site of the enzyme faces outside the cells, i.e. it is an ectoenzyme. Other than endothelial cells, ECE was also present in some secretory cells. The enzyme was abundant in the adrenal gland, and localized in chromaffin cells. ECE was also highly condensed in pancreatic islet beta cells. It is concluded that ECE and endothelin may be involved in the regulated secretion of hormones.

Adrenal Glands↗
PubMed1995

Identification of endothelin 1 and big endothelin 1 in secretory vesicles isolated from bovine aortic endothelial cells.

Vesicles containing endothelin 1 (ET-1) were isolated from bovine aortic endothelial cells (BAECs) by fractionation of homogenates on sucrose density gradients by ultracentrifugation. The vesicles were localized at the 1.0/1.2 M sucrose interface using a specific anti-ET-1-(16-21) RIA. Identification of ET-1 and big ET-1 in this fraction was confirmed by HPLC analysis combined with RIA. Morphological examination of the ET-1-enriched fraction by electron microscopy identified clusters of vesicles approximately 100 nm in diameter. Immunostaining of ultrathin cryosections prepared from the vesicle fraction for ET-1 or big ET-1 showed clusters of 15-nm gold particles attached to or within vesicles. Immunofluorescence staining of whole BAECs using a specific ET-1-(16-21) IgG purified by affinity chromatography revealed punctate granulation of the cell cytoplasm viewed under light microscopy. This distinct pattern of staining was shown by confocal light microscopy to be intracellular. Immunofluorescence staining of whole cells with a polyclonal antiserum for big ET-1-(22-39) showed a defined perinuclear localization of precursor molecule. Hence, several different approaches have demonstrated that ET-1 and big ET-1 are localized within intracellular vesicles in BAECs, suggesting that these subcellular compartments are an important site for processing of big ET-1 by endothelin-converting enzyme.

Animals↗
PubMed1995

Endopeptidase-24.11 is the integral membrane peptidase initiating degradation of somatostatin in the hippocampus.

The membrane metalloenzyme endopeptidase-24.11 has been localized by immunocytochemistry in the porcine hippocampus in the stratum oriens and stratum radiatum. Endopeptidase-24.11 was found to be approximately 10-fold more abundant in a striatal than a hippocampal membrane preparation. Both somatostatin-28 and somatostatin-14 were metabolized by endopeptidase-24.11, but the kinetics of hydrolysis markedly favoured the smaller form of the neuropeptide. After phase separation with Triton X-114 of striatal and hippocampal membrane preparations, and by using selective inhibitors, the major (> 80%) somatostatin-metabolizing activity was found to partition into the detergent-rich phase and was attributable predominantly to endopeptidase-24.11. The residual activity observed in the presence of the selective endopeptidase-24.11 inhibitor phosphoramidon was blocked by Pro-Ile or N-[1-(RS)-carboxy-3-phenylpropyl]-Ala-Ala-Phe-p-aminobenzoate, inhibitors of endopeptidase-24.16 and endopeptidase-24.15, respectively. However, Pro-Ile, at comparable concentrations, was shown to inhibit endopeptidase-24.11, challenging the validity of its use as a selective inhibitor of endopeptidase-24.16. The immunocytochemical and Triton X-114 phase-separation data implicate endopeptidase-24.11, rather than endopeptidase-24.16 or endopeptidase-24.15, as the major physiological somatostatin-degrading neuropeptidase in the striatum and hippocampus.

Animals↗
PubMed1995

Clinical evaluation of CA-125 concentrations as a prognostic factor for pregnancy in infertile women with surgically treated endometriosis.

OBJECTIVE: To extend and confirm earlier observations that serial CA-125 determinations appear to have prognostic value in some infertile women with surgically treated endometriosis using a new automated enzyme immunoassay. DESIGN: A prospective consecutive case series. SETTING: A university-based tertiary practice. PATIENTS: Of 342 women having a laparoscopy for infertility, 123 (36%) had endometriosis. Fifty-six of 123 (45%) infertile women with endometriosis had preoperative CA-125 values > or = 16 U/mL and were followed for 12 months with serial CA-125 determinations. MAIN OUTCOME MEASURE: Proportion of women achieving a pregnancy within 12 months from surgery. RESULTS: Mean preoperative CA-125 concentrations were not statistically different for women conceiving, but mean postoperative CA-125 values were significantly lower for women achieving a pregnancy. Univariate analyses indicated that preoperative CA-125 values between 16-25 U/mL and postoperative CA-125 values < 16 U/mL were associated with significantly higher pregnancy rates. Multivariate analyses of 10 covariables indicated only postoperative CA-125 concentrations to be associated with pregnancy even after controlling for all covariables. CONCLUSION: Using a newly developed assay for CA-125, the study confirms and extends earlier observation that CA-125 concentrations have prognostic value for pregnancy in infertile women with surgically treated endometriosis. The findings provide additional support for the clinical use of CA-125 concentrations in selected women with endometriosis.

Adult↗
PubMed1995

Localization and biochemical characterization of endothelin-converting enzyme.

We used a variety of biochemical and immunologic techniques to investigate the localization of endothelin-converting enzyme (ECE) in porcine lung, in human umbilical vein endothelial cells (HUVECs), and in the transformed endothelial cell line EA.hy926. Phosphoramidon-sensitive ECE activity was not enriched on immunomagnetically separated angiotensin-converting enzyme (ACE)-bearing luminal endothelial membranes from pig lung, whereas ACE showed a sevenfold enrichment. ECE activity did, however, co-localize with aminopeptidase-N (AP-N) activity on isolated EA.hy926 plasma membranes. Using a monoclonal antibody to rat lung ECE (AEC32-326) and immunofluorescence microscopy, we have demonstrated ECE on the cell surface of endothelial cell lines.

Animals↗
PubMed1994

Localization of aminopeptidase N and dipeptidyl peptidase IV in pig striatum and in neuronal and glial cell cultures.

The subcellular distribution of the plasma membrane ectoenzymes, aminopeptidase N (aminopeptidase M) and dipeptidyl peptidase IV, has been examined by fractionating homogenates of porcine striata by a discontinuous Percoll gradient centrifugation procedure which distinguishes fractions containing pre- and post-synaptic elements. The two enzymes showed different distributions--dipeptidyl peptidase IV did not show a significant pre-synaptic location, whereas aminopeptidase N was present on both pre- and post-synaptic fractions. Immunofluorescent staining on mixed and neuron-enriched primary cultures of pig striatal tissue using affinity purified antibodies to the aminopeptidase and to the dipeptidyl peptidase revealed the ectoenzymes on distinct populations of cells. The astrocytic identity of the aminopeptidase N-staining cells was established by correlation with immunostaining for glial fibrillary acidic protein and for vimentin by confocal microscopy. Ultracryosections of striatum immunostained with gold-labelled immunoglobulins of differing diameters demonstrated aminopeptidase N on pericytes and confirmed its location on endothelial and astrocytic glial cells. Thus, several independent approaches indicated that aminopeptidase N, in addition to being present on endothelial and synaptic membranes, is found on astrocytes and pericytes in the perivascular neuropil, whereas dipeptidyl peptidase IV is less widely distributed on microvessels and appears not to have a synaptosomal location.

Aminopeptidases↗
PubMed1994

Tandem overproduction and characterisation of the nuclease domain of colicin E9 and its cognate inhibitor protein Im9.

We report the overproduction of the non-specific endonuclease domain of the bacterial toxin colicin E9 and its preliminary characterisation in vitro. The enzymatic colicins (61 kDa) are normally released from producing cells in a complex with their cognate inhibitors, known as the immunity proteins (9.5 kDa). Tryptic digestion of the purified ColE9 complex was found to generate two major components, a monomer derived from the N-terminal and central regions of the toxin and a heterodimer comprising the catalytically active C-terminal domain of the colicin bound to its intact immunity protein, Im9. N-terminal amino acid sequencing, in conjunction with electrospray mass spectrometry, shows that preparations of the DNase domain isolated by this method are heterogeneous, thus making subsequent mechanistic and structural analysis difficult. This problem was circumvented by selectively overexpressing the C-terminal 15-kDa nuclease domain of colicin E9 in tandem with its cognate inhibitor in Escherichia coli. This tandem overexpression strategy allowed high-level production of a 25-kDa protein complex comprising the C-terminal DNase domain of colicin E9 tightly bound to its specific inhibitor Im9, thus masking the anticipated toxicity of the nuclease. The DNase domain was then separated from Im9 under denaturing conditions, refolded by removal of the denaturant and the renatured protein shown to possess both endonuclease and Im9 binding activity. These results describe a novel method for the overproduction of a nuclease in bacteria by co-expressing its specific inhibitor and lay the foundations for a full mechanistic, biophysical and structural characterization of the isolated DNase domain of the colicin E9 toxin.

Amino Acid Sequence↗
PubMed1994

A selective N-type Ca(2+)-channel blocker prevents CA1 injury 24 h following severe forebrain ischemia and reduces infarction following focal ischemia.

SNX-111 (NEUREX Corporation, Menlo Park, CA, U.S.A.) an omega-conopeptide, was tested for cytoprotection following normothermic ischemia using both a four-vessel occlusion model of severe forebrain ischemia and a model of transient middle cerebral artery occlusion focal ischemia. Adult male Wistar rats were subjected to 10 min of forebrain ischemia followed by 7 days of reperfusion. A single dose of SNX-111 (5 mg/kg) was injected intravenously following delays of either 6 or 24 h after reperfusion. For 11 rats treated with saline, there was 78 +/- 13% CA1 neuronal injury (mean +/- SD); for 11 given SNX-111 delayed by 6 h, injury was reduced to 35 +/- 30% (p < 0.01); and remarkably, treatment delayed by 24 h (n = 10), still resulted in protection, with only 50 +/- 29% injury (p < 0.05). Adult male spontaneously hypertensive rats had transient occlusion of the right middle cerebral artery of 1.5- or 2-h duration followed by 22.5 or 22 h of reperfusion, respectively. Rats were randomly assigned to receive either saline or SNX-111 (5 mg/kg i.v.), with treatment starting immediately after reperfusion (1.5-h ischemic group) or at 1 h following the onset of ischemia (2-h ischemic group). In the 1.5-h ischemic group, saline-treated animals sustained 138 +/- 32 mm3 of neocortical infarction (n = 9), and SNX-111 treatment resulted in an infarct reduction to 76 +/- 25 mm3 (n = 9; p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Delayed treatment with AMPA, but not NMDA, antagonists reduces neocortical infarction.

We tested the abilities of two potent non-N-methyl-D-aspartate (non-NMDA) glutamate antagonists [2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)quinoxaline (NBQX)] and [1-(4-aminophenyl)-4-methyl-7,8-methylene-dioxy-5H-2,3-benzodiazep ine hydrochloride (GYKI 52466)] to reduce neocortical infarction following 2 h of transient middle cerebral artery occlusion in a hypertensive stroke model in the rat and compared these effects against, and in combination with, a potent NMDA antagonist [(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-amine maleate (MK-801)]. In Expt. 1, an already established cytoprotective dose of Na(+)-NBQX (30 mg/kg i.p. x 3) was compared with saline (1 ml), the NMDA antagonist MK-801 (1 mg/kg i.p. x 3), and a combination of the same doses of both NBQX and MK-801. Initial doses were delayed to 90 min following occlusion with subsequent injections at the time of reperfusion and 30 min following reperfusion. Saline-treated rats sustained 181 +/- 32 mm3 (n = 15) of neocortical infarction (mean +/- SD). This was significantly reduced by NBQX to 137 +/- 25 mm3 (n = 15, p < 0.05) of damage. Neither MK-801 (170 +/- 33 mm3; n = 11) nor the combination of MK-801 and NBQX (169 +/- 20 mm3; n = 6) proved to be cytoprotective when given with a 90-min delay. In Expt. 2, NBQX (30 mg/kg) was dissolved (6 mg/ml) in 5% dextrose and compared with both saline and dextrose (1.2 ml) i.v. infusions given over a 4-h period starting 1 h after occlusion. Saline-treated rats had a mean infarct of 183 +/- 27 mm3 (n = 6), dextrose-treated had 200 +/- 30 mm3 (n = 9), while for NBQX-treated rats it was reduced to 129 +/- 60 mm3 (n = 10, p < 0.05). Intravenous NBQX precipitated into the renal tubules, causing nephrotoxicity. In Expt. 3, rats were given either saline (1 ml i.p.) or GYKI 52466 (10 mg/kg i.p.) at 30 and 90 min following occlusion and at 30, 90, and 150 min following reperfusion. Saline-treated rats sustained 187 +/- 27 mm3 of neocortical infarction (n = 7), while those treated with GYKI 52466 were protected, with 139 +/- 38 mm3 of infarction (n = 7, p < 0.05). A clinically useful role for alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate antagonists in embolic stroke is envisaged if nontoxic drugs can be developed, since cerebroprotection was achieved with delayed treatment with both of these lead compounds.

Animals↗