22,836 results for 2000

  • The perception and preferences and preferences of parents of children with tracheostromies in a study of humidification therapy

    McNamara, David; Dickinson, Annette; Byrnes, Catherine (2009-09-01)

    Journal article
    The University of Auckland Library

    This article reports a grounded theory study which was the qualitative phase of a randomized-controlled trial in children with tracheostomies comparing two techniques for providing humidified inspired gases. Semi-structured interviews were conducted with eight mothers of children with tracheostomies recruited from the trial, one mother who was not involved in the trial and four experienced nurses. Data were analysed using open, selective and theoretical coding. A core category was identified of parents managing the child???s care in response to a set of problematic and constraining states. Parents were seen to utilize strategies of constant checking, becoming the expert, the family pulling together and electing to use preferred technology. The findings of this study mirror those of previous studies and reinforce the primacy of caregivers as managers of their child???s health care. Mothers elected to use or not use a given technology within this context, utilizing a process of balancing.

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  • Ground-penetrating radar and sedimentological analysis of Holocene floodplains: insight from the Tuross valley, New South Wales

    Nobes, DC; Ferguson, RJ; Brierley, Gary (2001-06-01)

    Journal article
    The University of Auckland Library

    Ground???penetrating radar (GPR) has been used on an array of floodplain types on the lower Tuross River, in southeastern New South Wales, as part of an investigation into controls on channel???floodplain relationships. Ground???penetrating radar transects from two floodplains are presented, along with sedimentological detail from trenches dug along the profiles at key locations. Sedimentological investigations showed that 100 MHz antenna gave an approximation of overall bedding trends in the upper 3 m when automatic gain control processing was used. Spreading and exponential compensation processing provided insight into textural changes associated with increased silt content distal of the levee crest. One trench showed that thinning beds were responsible for onlapping reflectors. Signal attenuation at ???4 m depth below the raised floodplain surface resulted from a >50 cm???thick bed of sandy clay. The close integration of GPR and sedimentological data produced an excellent dataset, that enabled form???process associations and floodplain evolution to be established for these sandy floodplains. However, accurate subsurface assessment and interpretation must stem from carefully combined GPR and sedimentological datasets.

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  • Clear-water scour development at bridge abutments

    Coleman, Stephen; Lauchlan, Christine; Melville, Bruce (2003)

    Journal article
    The University of Auckland Library

    Abstract Development of local scour depths at vertical-wall bridge abutments of varying lengths was investigated in several series of experiments of ranges of uniform sediments and clear-water flow intensities. For each flow-abutment-sediment combination tested, the change with time in maximum local scour depth from plane-bed to equilibrium conditions was recorded and analysed. The results of similar earlier abutment-scour experimental studies were also incorporated in analyses of scour development. Variations in scour rates and depths with flow and sediment parameters are found to be different for short (flow depth/abutment length = y/L > 1) and long (y/L ??? 1) abutments. In order to provide a consistent framework for assessment of the development of scour depth with time, a revised definition of the time to achieve equilibrium conditions is developed. Based on this definition, the dimensionless time to equilibrium for scour development from plane-bed conditions can be expressed as a function of relative flow intensity and relative abutment length. This expression can be adopted into existing methodologies to predict scour magnitudes occurring at bridge abutments. Utilising extensive data sets, expressions enabling the determination of scour depths at abutments, and also piers, are reassessed for the present definition of time to achieve equilibrium conditions. Application of the developed expressions is highlighted in an example.

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  • Rheumatic heart disease detected by echocardiographic screening

    Webb, Rachel; Wilson, N; Lennon, Diana (2007-11-15)

    Journal article
    The University of Auckland Library

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  • Stratigraphy, age and correlation of middle Pleistocene silicic tephras in the Auckland region, New Zealand: A prolific distal record of Taupo Volcanic Zone volcanism

    Alloway, Brent; Westgate, J; Pillans, B; Pearce, N; Newnham, R; Byrami, M; Aarburg, S (2004)

    Journal article
    The University of Auckland Library

    Coastal sections in the Auckland region reveal highly carbonaceous and/or highly weathered clay???dominated cover???bed successions with numerous discrete distal volcanic ash (tephra) layers, fluvially reworked siliciclastic (tephric) deposits, and two widely distributed pyroclastic density current (PDC) deposits generated from explosive silicic volcanism within the Taupo Volcanic Zone (TVZ). The younger of the two PDC deposits (informally named Waiuku tephra) is glass???isothermal plateau fission???track (ITPFT) dated at 1.00 ?? 0.03 Ma and occurs in a normal polarity interval interpreted as the Jaramillo Subchron. Waiuku tephra is correlated with Unit E sourced from the Mangakino Volcanic Centre of the TVZ. Waiuku tephra can be subdivided into two distinctive units enabling unequivocal field correlation: a lower stratified unit (dominantly pyroclastic surge with fall component) and an upper massive to weakly stratified unit (pyroclastic flow). At many sites in south Auckland, Waiuku tephra retains basal ???surge???like??? beds (<1.4 m thickness). This provides clear evidence for primary emplacement and is an exceptional feature considering the c. 200 km this PDC has travelled from its TVZ source area. However, at many other Auckland sites, Waiuku tephra displays transitional sedimentary characteristics indicating lateral transformation from hot, gas???supported flow/surge into water???supported mass flow and hyperconcentrated flow (HCF) deposits. The older PDC deposit is dated at 1.21 ?? 0.09 Ma, is enveloped by tephras that are ITPFT???dated at 1.14 ?? 0.06 Ma (above) and 1.21 ?? 0.06 Ma (below), respectively, and occurs below a short normal polarity interval (Cobb Mountain Subchron) at c. 1.19 Ma. This PDC deposit, correlated with Ongatiti Ignimbrite sourced from the Mangakino Volcanic Centre of TVZ, has laterally transformed from a gas???supported, fine???grained pyroclastic flow deposit at Oruarangi, Port Waikato, into a water???supported volcaniclastic mass flow deposit farther north at Glenbrook Beach. The occurrence of Ongatiti Ignimbrite in Auckland significantly extends its northward distribution. Large numbers of post??? and pre???Ongatiti rhyolitic tephra layers, ranging in age from c. 1.31 to 0.53 Ma, are also recognised in the region, with some up to 0.5 m in compacted fallout thickness. Although some tephras can be attributed to known TVZ eruptions (e.g., Ahuroa/Unit D), many have yet to be identified in proximal source areas and remain uncorrelated. However, some can be reliably correlated to tephra layers occurring in marine to nearshore sequences of Wanganui Basin and deep???sea cores retrieved east of North Island. The identification of previously unrecognised mid???Pleistocene TVZ???sourced tephra deposits in the Auckland region, and their correlation to the offshore marine record, represent an advance in the construction of a higher resolution history for the TVZ where, close to eruptive source, the record is fragmentary and obscured by deep burial, or erosion, or both.

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  • Deep???ocean record of major late Cenozoic rhyolitic eruptions from New Zealand

    Carter, L; Alloway, Brent; Shane, P; Westgate, J (2004-09)

    Journal article
    The University of Auckland Library

    A 12 m.y. record of large rhyolitic eruptions from the Coromandel (CVZ) and Taupo (TVZ) Volcanic Zones of New Zealand is contained in cores retrieved by Leg 181 of the Ocean Drilling Program. Site 1124, located 670 km from the TVZ, has a maximum of 134 macroscopic tephra layers with a total thickness of 13.18 m. These units, along with between 7 and 63 tephras from 3 other sites, were dated by a combination of magnetostratigraphy, biostratigraphy, isothermal plateau fission track determinations, and geochemical correlation with onshore tephra deposits. Additional time control for the last 3 m.y. came from an orbitally tuned, benthic, oxygen isotope profile for Site 1123. Results extend the incomplete terrestrial record of volcanism by placing the first major rhyolitic eruption in the CVZ at c. 12 Ma, c. 1.6???1 m.y. earlier than previously known. Tephras became thicker and more frequent from the late Miocene into the Quaternary???a trend that probably reflected (1) more frequent and intense volcanism and (2) reduced distances between sources and depositional sites on the evolving Australian/Pacific plate system. The passage from CVZ to Quaternary TVZ occurred without a major hiatus in activity, suggesting the transition was gradational. The ensuing TVZ volcanism was more continuous than known previously from the onshore geology. Ash dispersal was primarily eastward, highlighting the dominance of westerly winds since the middle Miocene. Nevertheless, variations in dispersal patterns suggest periodic changes in wind direction/speed and/or ejection of ash beyond the Roaring Forties.

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  • IT Industry Success in Small Countries: The Cases of Finland and New Zealand

    Watson, R; Myers, Michael (2001-04)

    Journal article
    The University of Auckland Library

    Given the importance of the information technology industry in today???s global economy, much recent research has focused on the relative success of small countries in fostering IT industries. This article examines the factors of IT industry success in small developed countries, and compares two such countries, Finland and New Zealand. Finland and New Zealand are alike in many respects, yet Finland???s IT industry is more successful than New Zealand???s. Three major factors that impact on the development of a successful IT industry are identified: the extent of government IT promotion, the level of research and development, and the existence of an education system that produces IT literate graduates.

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  • Demise of one volcanic zone and birth of another???A 12 m.y. marine record of major rhyolitic eruptions from New Zealand

    Carter, LC; Shane, Philip; Alloway, Brent; Hall, IR; Harris, SE; Westgate, JA (2003-06)

    Journal article
    The University of Auckland Library

    Ocean Drilling Program Sites 1123 and 1124 provide an unprecedented 12 m.y. record of major rhyolitic eruptions from the Coromandel and Taupo volcanic zones of New Zealand. Macroscopic tephras (n = 197) were dated using magnetostratigraphy, supplemented by geochemical correlation with subaerial tephra, isothermal plateau fission-track ages, and orbitally tuned stable isotope data. Eruptions began in the Coromandel volcanic zone ca. 12 Ma, ???1.6???1 m.y. earlier than previously known. Thereafter, volcanism was fairly continuous with a tempo and intensity that increased through the late Miocene???Pliocene and into the Quaternary, when the Taupo volcanic zone formed. The transition from the Coromandel to the Taupo zone, previously placed as ca. 4???2 Ma, was seamless, without obvious breaks or changes in ash composition. This well-dated history of long-lived and productive volcanism allows for more confident correlation with other circum-Pacific tephra records, thus helping confirm the occurrence of widespread coeval eruptions throughout the region.

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  • IT industry development and the knowledge economy: A four country study

    Ein-Dor, P; Myers, Michael; Raman, KS (2004)

    Journal article
    The University of Auckland Library

    It is generally accepted that knowledge has become a third major factor of production, in addition to the traditional factors ??? labor and capital. Information technology production is a significant factor in the knowledge economy both because it is a major enabler of that economy and because it is itself highly knowledge intensive. Many countries around the world are looking for ways to promote the development of the knowledge economy, and information technology industries in particular. An important question is to what extent ??? and how ??? small developed countries might succeed in this endeavor. This study suggests a modified and more comprehensive version of the Ein-Dor et al. (1997) model of IT (information technology) industry success in small developed countries. Whereas the earlier model of IT industry success was based solely on the macro-economic theory of Grossman and Helpman (1991), the revised model suggested here incorporates Romer???s (1990) work in New Growth economics. A significant advance over earlier work in this area is the use of both longitudinal and time slice data. This article provides an in-depth analysis of the IT industry in four countries over a five-year period: Finland, Israel, New Zealand and Singapore. It analyses some changes that occurred over the period 1994 through 1998 and thus provides a reasonably comprehensive picture of the factors affecting the production of IT in these small developed countries. Our study reveals that four of the five endogenous variables studied have a close relationship to the development of IT industries in small developed countries. These variables are research and development, technological infrastructure, firm strategies, and capital availability. On the other hand, domestic IT use does not seem to be a major factor in IT industry development. Our analysis thus largely supports the more comprehensive model of IT industry success. These findings should be of interest to both researchers and policy makers seeking to develop the knowledge economy and information technology industries in particular.

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  • The Right to Language and its Contemporary Significance for New Zealand

    Connell, Charlotte (2006)

    Scholarly text
    Victoria University of Wellington

    The right of linguistic minorities to speak their own language in community with other members of their group (the right to language) is deserving of specific attention for two reasons. Firstly, language is the currency of communication and one of the key indicia of cultural identity; and secondly, ensuring minorities have a secure place within a State is pivotal to promoting peace and stability within a nation. There are three sources of the right to language in New Zealand : the International Covenant on Civil and Political rights, the New Zealand Bill of Rights Act 1990, and the Treaty of Waitangi (for the Maori and Moriori languages). The right to language protects against both direct action by the State to limit linguistic minorities' use of their language. and State neglect of a minority language. This paper explores the right to language in the New Zealand context including the sources and elements of the right to language; the application of the right to the Maori language (and what lessons can be learned from this experience for the Moriori language); and two modes of revitalisation of minority languages: official recognition and television broadcasting. The paper observes that while the steps to improve language acquisition and use of the Maori language are admirable and need to continue to secure a meaningful place for that language in New Zealand, the Moriori language is in serious jeopardy and in need of urgent attention. Finally, the paper examines whether the principles of the Treaty of Waitangi may provide sound guidance for the consideration of the place of minority languages in policy and law making in New Zealand.

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  • Safety of bronchoalveolar lavage in young children with cystic fibrosis.

    Wainwright, CE; Grimwood, K; Carlin, JB; Vidmar, S; Cooper, PJ; Francis, PW; Byrnes, Catherine; Whitehead, BF; Martin, AJ; Robertson, IF; Cooper, DM; Dakin, CJ; Masters, IB; Massie, RJ; Robinson, PJ; Ranganathan, S; Armstrong, DS; Patterson, LK; Robertson, CF (2008-10)

    Journal article
    The University of Auckland Library

    Objective: Our aim was to determine the safety of BAL in young children <38.5??C). Low percentage BAL return (P???=???0.002) and focal bronchitis (P???=???0.02) were associated with clinically significant deterioration. Multivariable analysis identified Streptococcus pneumoniae (OR 22.3; 95% confidence interval (CI); 6.9,72), Pseudomonas aeruginosa (OR 2.4; 95% CI 1.0, 5.8), respiratory signs (OR 5.0; 95% CI 1.7, 14.6) and focal bronchitis (OR 5.9; 95% CI 1.2, 29.8) as independent risk factors for post-bronchoscopy fever ???38.5??C. Conclusions: Adverse events are common with BAL in young CF children, but are usually transient and well tolerated. Parents should be counseled that signs of a pre-existing lower respiratory infection are associated with increased risk of post-BAL fever.

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  • Novel neutrophil-derived proteins in bronchoalveolar lavage fluid indicate an exaggerated inflammatory response in pediatric cystic fibrosis patients

    McMorran, BJ; Ouvry Patat, SA; Carlin, JB; Grimwood, K; Jones, A; Armstrong, DS; Galati, JC; Cooper, PJ; Byrnes, Catherine; Francis, PW; Robertson, CF; Hume, DA; Borchers, CH; Wainwright, CE; Wainwright, BJ (2007-10)

    Journal article
    The University of Auckland Library

    Background: Airway inflammation in cystic fibrosis (CF) is exaggerated and characterized by neutrophil-mediated tissue destruction, but its genesis and mechanisms remain poorly understood. To further define the pulmonary inflammatory response, we conducted a proteome-based screen of bronchoalveolar lavage fluid (BALF) collected from young children with and without CF experiencing endobronchial infection. Methods: We collected BALF samples from 45 children younger than 5 years and grouped them according to the presence of respiratory pathogens: ???1 ?? 105 colony-forming units (CFU)/mL BALF (18 and 12 samples with and without CF, respectively) and <1 ?? 105 CFU/mL (23 and 15 samples). BALF proteins were analyzed with SELDI-TOF mass spectrometry (MS) and H4 ProteinChips??. Proteins were identified and characterized using trypsin digestion, tandem MS, Fourier transform ion cyclotron resonance MS, immunoblotting, and ELISA. Results: The SELDI-TOF MS BALF profiles contained 53 unique, reliably detected proteins. Peak intensities of 24 proteins differed significantly between the CF and non-CF samples. They included the neutrophil proteins, ??-defensin 1 and 2, S100A8, S100A9, and S100A12, as well as novel forms of S100A8 and S100A12 with equivalent C-terminal deletions. Peak intensities of these neutrophil proteins and immunoreactive concentrations of selected examples were significantly higher in CF than non-CF samples. Conclusions: Small neutrophil-derived BALF proteins, including novel C-terminal truncated forms of S100A proteins, are easily detected with SELDI-TOF MS. Concentrations of these molecules are abnormally high in early CF lung disease. The data provide new insights into CF lung disease and identify novel proteins strongly associated with CF airway inflammation.

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  • Religion, gossip, narrative conventions and the construction of meaning in Hindi film songs.

    Booth, Gregory (2000)

    Journal article
    The University of Auckland Library

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  • Characterisation of dihydrodipicolinate synthase (DHDPS) from Bacillus anthracis

    Domigan, Laura; Scally, SW; Fogg, MJ; Hutton, CA; Perugini, MA; Dobson, RCJ; Muscroft-Taylor, AC; Gerrard, Juliet; Devenish, SRA (2009-10)

    Journal article
    The University of Auckland Library

    Bacillus anthracis is a Gram-positive spore-forming bacterium that is the causative agent of anthrax disease. The use of anthrax as a bioweapon has increased pressure for the development of an effective treatment. Dihydrodipicolinate synthase (DHDPS) catalyses the first committed step in the biosynthetic pathway yielding two essential bacterial metabolites, meso-diaminopimelate (DAP) and (S)-lysine. DHDPS is therefore a potential antibiotic target, as microbes require either lysine or DAP as a component of the cell wall. This paper is the first biochemical description of DHDPS from B. anthracis. Enzyme kinetic analyses, isothermal titration calorimetry (ITC), mass spectrometry and differential scanning fluorimetry (DSF) were used to characterise B. anthracis DHDPS and compare it with the well characterised Escherichia coli enzyme. B. anthracis DHDPS exhibited different kinetic behaviour compared with E. coli DHDPS, in particular, substrate inhibition by (S)-aspartate semi-aldehyde was observed for the B. anthracis enzyme (K(si(ASA))=5.4+/-0.5 mM), but not for the E. coli enzyme. As predicted from a comparison of the X-ray crystal structures, the B. anthracis enzyme was not inhibited by lysine. The B. anthracis enzyme was thermally stabilised by the first substrate, pyruvate, to a greater extent than its E. coli counterpart, but has a weaker affinity for pyruvate based on enzyme kinetics and ITC studies. This characterisation will provide useful information for the design of inhibitors as new antibiotics targeting B. anthracis.

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  • Contractile function in vitro of slow-twitch skeletal muscle from weanling mice subjected to wasting malnutrition

    Fischer, JW; Reading, Stacey; Hillyer, L; Woodward, B; Barclay, JK (2001-06)

    Journal article
    The University of Auckland Library

    Our hypothesis was that malnutrition sufficient to produce weight loss in weanling mice would decrease the ability of slow-twitch skeletal muscle to develop and maintain force. We isolated muscles from 3 groups (n = 5) of weanling C57BL/6J mice of both sexes (i) mice at 19 days of age serving as zero-time or baseline controls (CONT) (ii) mice fed for the next 14 days with a low-protein diet that produces features of incipient kwashiorkor (LPD) and (iii) mice fed for the next 14 days with a complete diet (NORM). Muscles were also obtained from 5 adult mice 7-9 months of age (MAT). We stimulated the soleus at 50 Hz for 500 ms at 0.6 tetanic contractions per min (tet x min(-1)), 6 tet x min(-1), and 30 tet x min(-1) in Krebs-Henseleit bicarbonate buffer at 27 degrees C gassed with 95% O2 and 5% CO2. The initial developed force (mN x mm(-2)) at 0.6 tet x min(-1) did not differ across groups (CONT 211.7 +/- 16.0, LPD 274.2 +/- 41.6, NORM 246.8 +/- 38.0, MAT 210.8 +/- 10.6). The fatigue rate (mN x mm(-2) x min(-1)) at 6 tet x min(-1) was significantly slower in muscles from CONT (0.6 +/- 0.3) and LPD (0.6 +/- 0.4) than in NORM (2.4 +/- 0.6) and MAT (2.3 +/- 0.2). At 30 tet x min(-1), the fatigue rate (mN x mm(-2) x min(-1)) did not differ across groups (CONT 2.4 +/- 0.5, LPD 2.7 +/- 0.5, NORM 2.5 +/- 0.4, MAT 2.0 +/- 0.2). After stimulation at 6 tet x min(-1) and 30 tet x min(-1), only muscles from CONT and LPD recovered to 100%. Because muscles from LPD mice developed equal force, fatigued less, and recovered from fatigue to a greater extent than muscles from NORM mice, we rejected the hypothesis. The function of the tissue remaining in the muscles from LPD mice approximated that of muscles from mice at 19 days of age rather than muscles from either mice of the same age fed a complete diet or adult mice.

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  • Positive inotropism in mammalian skeletal muscle in vitro during and after fatigue

    Reading, Stacey; Murrant, CL; Barclay, JK (2004-04)

    Journal article
    The University of Auckland Library

    We tested the hypothesis that positive inotropic factors decrease fatigue and improve recovery from fatigue in mammalian skeletal muscle in vitro. To induce fatigue, we stimulated mouse soleus and extensor digitorum longus (EDL) to perform isometric tetanic contractions (50 impulses x s(-1) for 0.5 s) at 6 contractions x min(-1) for 60 min in soleus and 3 contractions x min(-1) for 20 min in EDL. Muscles were submerged in Krebs-Henseleit bicarbonate solution (Krebs) at 27 degrees C gassed with 95% nitrogen - 5% carbon dioxide (anoxia). Before and for 67 min after the fatigue period, muscles contracted at 0.6 contractions x min(-1) in 95% oxygen - 5% carbon dioxide (hyperoxia). We added a permeable cAMP analog (N6, 2'-O-dibutyryladenosine 3':5'-cyclic monophosphate at 10(-3) mol x L(-1) (dcAMP)), caffeine (2 x 10(-3) mol x L(-1), or Krebs as vehicle control at 25 min before, during, or at the end of the fatigue period. In soleus and EDL, both challenges added before fatigue significantly increased developed force but only caffeine increased developed force when added during the fatigue period. At the end of fatigue, the decrease in force in challenged muscles was equal to or greater than in controls so that the force remaining was the same or less than in controls. EDL challenged with dcAMP or caffeine at any time recovered more force than controls. In soleus, caffeine improved recovery except when added before fatigue. With dcAMP added to soleus, recovery was better after challenges at 10 min and the end of the fatigue period. Thus, increased intracellular concentrations of cAMP and (or) Ca2+ did not decrease fatigue in either muscle but improved recovery from fatigue in EDL and, in some conditions, in soleus.

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  • Central role of TRPM4 channels in cerebral blood flow regulation

    Reading, Stacey; Brayden, JE (2007-08)

    Journal article
    The University of Auckland Library

    The transient receptor potential channel TRPM4 is critically linked to the myogenic constrictor response of cerebral arteries that occurs when intravascular pressure increases. This myogenic behavior is thought to be fundamentally involved in the mechanisms of blood flow autoregulation. In this study, we tested the hypothesis that TRPM4 channels in cerebrovascular myocytes contribute to cerebral blood flow autoregulation in vivo.In vivo suppression of cerebrovascular TRPM4 expression was achieved by infusing antisense oligodeoxynucleotides into the cerebral spinal fluid of 400- to 550-g Sprague-Dawley rats at 80 microg x day(-1) for 7 days using an osmotic pump that discharged into the lateral cerebral ventricle. Absolute cerebral blood flow measurements were obtained over a range of mean arterial pressures using fluorescent microsphere methods.Oligonucleotides infused into the cerebrospinal fluid were detected in the smooth muscle cells of pial arteries. Semi-quantitative RT-PCR indicated that the message for TRPM4 was decreased in the cerebral arteries of antisense-treated rats. Myogenic constriction was decreased by 70% to 85% in cerebral arteries isolated from TRPM4 antisense- compared with control sense-treated rats. Cerebral blood flow was significantly greater in TRPM4 antisense- versus sense-treated rats at resting and elevated mean arterial pressures, indicating that autoregulatory vasoconstrictor activity was compromised in TRPM4 antisense-treated animals.In vivo suppression of TRPM4 decreases cerebral artery myogenic constrictions and impairs autoregulation, thus implicating TRPM4 channels and myogenic constriction as major contributors to cerebral blood flow regulation in the living animal.

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  • Inotropic effects on mammalian skeletal muscle change with contraction frequency

    Barclay, JK; Reading, Stacey; Murrant, CL; Woodley, NE (2003-08)

    Journal article
    The University of Auckland Library

    Over the last decade, we have attempted to determine if mammalian skeletal muscle's steady-level force development as established by mechanical and stimulation parameters can be increased or decreased by physiological signals. In these experiments, nitric oxide (NO), endothelin-1 (ET-1), adenosine (Ado), and beta-adrenergic agonists (beta) modified force production in the soleus and (or) the extensor digitorum longus (EDL) of the mouse. NO and beta increased the force produced by 0.5-s tetanic contractions at 0.6 contractions/min in both muscles. While EDL did not respond to either Ado or ET-1, the developed force of the soleus was amplified by Ado but attenuated by ET-1. Increased cAMP analogue concentrations amplified developed force in both muscles, but a cGMP analogue had no effect on either muscle. Following an increase in the contraction frequency of the soleus, the increased force in response to NO disappeared, as did the decreased force to ET-1. The increase in force due to a cAMP analogue disappeared during fatigue but reappeared quickly during recovery. Thus, steady-level developed force can be modified by a number of substances that can be released from locations in the body or muscle. The response to a given compound is determined by a complex interaction of metabolic and intracellular signals on the force-generating cascade.

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  • A1 receptor activation decreases fatigue in mammalian slow-twitch skeletal muscle in vitro

    Reading, Stacey; Barclay, JK (2001-06)

    Journal article
    The University of Auckland Library

    To test the hypothesis that adenosine improves skeletal muscle cell function, we exposed curarized mouse soleus and extensor digitorum longus (EDL) to a range of concentrations of adenosine (10 9 M to 10 5 M). Muscles contracted in Krebs-Henseleit bicarbonate buffer (27??C, 95% O2 and 5% CO2) for 500 ms at 50 Hz once every 90 s. Soleus fatigued significantly less with adenosine present at concentrations of 10 8 M and higher than with the Krebs-Henseleit vehicle control. Adenosine significantly improved force generation or delayed fatigue of EDL only with the initial adenosine challenge. To investigate the receptor population involved, we exposed soleus to agonists specific for A1 receptors (N6-cyclopentyladenosine, CPA), or A2 receptors (CGS 21680 hydrochloride, CGS), or A3 receptors (N6-benzyl-5'-N-ethylcarboxamidoadenosine, BNECA). CPA (A1) significantly decreased fatigue compared with the Krebs-Henseleit vehicle control at concentrations of 10 9 M and higher. Muscles exposed to the A2 and A3 agonists did not differ from a Krebs-Henseleit plus methanol control. Phenylephrine (10 6 M), an alpha-adrenergic agonist that increases the concentration of inositol triphosphate (IP3), significantly improved developed force in soleus. Neither a permeable cAMP analog, 8-bromo-cAMP (10 5 M), nor a beta1 agonist, isoproterenol (10 6 M), had an effect on force generation in the soleus when compared with a saline control. Thus adenosine slowed fatigue in slow-twitch skeletal muscle through A1 receptors.Key words: N6-cyclopentyladenosine, CGS 21680 hydrochloride, N6-benzyl-5'-N-ethylcarboxamidoadenosine, mouse skeletal muscle in vitro.

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  • Increased cAMP as a positive inotropic factor for mammalian skeletal muscle in vitro

    Reading, Stacey; Murrant, CL; Barclay, JK (2003-10)

    Journal article
    The University of Auckland Library

    To test the hypothesis that an increased cAMP concentration improves skeletal muscle force development, we stimulated mouse soleus and extensor digitorum longus (EDL) in the presence of isoproterenol (1 x 10(-5) mol.L-1), a beta-adrenergic agonist, or N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (dcAMP) (1 x 10(-3) mol.L-1), a membrane-permeable cAMP analogue. Drugs used in the challenges were dissolved in Krebs-Henseleit bicarbonate buffer (Krebs) at 27 degrees C and gassed with 95% O2 - 5% CO2. Stimulation at 50 impulses.s-1 for 0.5 s produced an isometric tetanic contraction. Over 25 min of contractions at 0.6 contractions.min-1, developed force increased significantly with the addition of isoproterenol (soleus, 2.5% +/- 1.1%; EDL, 13.8% +/- 2.0%) or dcAMP (soleus, 2.3% +/- 0.5%; EDL, 10.9% +/- 1.9%) as compared with vehicle controls (cont) with Krebs added (soleus, 0.0% +/- 0.2%; EDL, -2.5% +/- 0.7%). To investigate the role of Ca2+ availability, we amplified or attenuated sarcolemmal L-type Ca2+ channels with Bay K 8644 (Bay K) (5.6 x 10(-6) mol.L-1) or diltiazem hydrochloride (dilt) (10(-4) mol.L-1), respectively. Ca2+ release from the sarcoplasmic reticulum was increased with caffeine (2 x 10(-3) mol.L-1) or decreased with dantrolene sodium (dant) (4.2 x 10(-7) mol.L-1). With Ca2+availability modified, dcAMP addition in soleus significantly increased force development above control (cont, 2.3% +/- 0.4%; Bay K, 4.0% +/- 1.0%; dilt, 52.3% +/- 3.6%; caffeine, 2.3% +/- 0.7%; dant, 6.0% +/- 2.0%; dilt + dant, 55.0% +/- 23.0%). In EDL, the addition of dcAMP also increased force development above control (cont, 13.7% +/- 1.9%; Bay K, 17.0% +/- 4.0%; dilt, 170.0% +/- 40.0%; caffeine, 23.0% +/- 4.0%; dant, 72.0% +/- 10.0%; dilt + dant, 54.0% +/- 14.0%). Thus, a positive inotropic effect of cAMP existed in both fast- and slow-twitch mammalian skeletal muscle with both normal and altered Ca2+ flux into the sarcoplasm.

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