The Experts below are selected from a list of 1833 Experts worldwide ranked by ideXlab platform
Conchita Vens - One of the best experts on this subject based on the ideXlab platform.
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Role for DNA polymerase beta in response to ionizing radiation
Cancer Research, 2007Co-Authors: Christie Vermeulen, Manon Verwijs-janssen, Patricia Cramers, Adrian C. Begg, Conchita VensAbstract:3903 Evidence for a role of DNA polymerase beta in determining radiosensitivity is conflicting. In vitro assays show an involvement of DNA polymerase beta in single strand break repair and base excision repair of oxidative damage, both products of ionizing radiation. Nevertheless the lack of DNA polymerase beta has been shown to have no effect on radiosensitivity. Here we show that mouse embryonic fibroblasts deficient in DNA polymerase beta are considerably more sensitive to ionizing radiation than wild-type cells, but only when confluent. The data indicates that replication associated repair is independent of DNA polymerase beta, and when replication is low, repair of DNA damage induced by ionizing radiation depends on DNA polymerase beta. To further strengthen our hypothesis, we synchronized wild-type and polymerase beta deficient cells with ‘mitotic shake off’ and found that DNA polymerase beta deficient cells are more sensitive to ionizing radiation than wild-type cells in G1 phase of the cell cycle, but radiosensitivity of DNA polymerase beta deficient cells decreased when cells progressed from G1 to S phase. No difference in radiosensitivity between wild-type and polymerase beta deficient cells was observed in S phase, showing that redundant pathways are active in replicating cells only. To characterize these pathways further, we used the inhibitor methoxyamine that renders abasic sites refractory to the dRP lyase activity of DNA polymerase beta. Methoxyamine did not significantly change radiosensitivity of wild-type fibroblasts in log phase. However, DNA polymerase beta deficient cells in log phase were radiosensitized by methoxyamine. Alkaline comet assays confirmed repair inhibition of ionizing radiation induced damage by methoxyamine in these cells, indicating both the existence of a polymerase beta-dependent long patch pathway and the involvement of another methoxyamine sensitive process, implying the participation of a second short patch polymerase(s) other than DNA polymerase beta. This is the first evidence of a role for DNA polymerase beta in radiosensitivity in vivo. To further investigate the possibility of a second short patch pathway, we are currently studying DNA polymerases iota and lambda, both translesion synthesis polymerases which have enzymatic and structural similarities to DNA polymerase beta. Knockdown and overexpression experiments are being performed to reveal the possible contribution of DNA polymerase iota and lambda to single strand break repair and base excision repair after ionizing radiation.
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Role for DNA polymerase beta in response to ionizing radiation
DNA repair, 2006Co-Authors: Christie Vermeulen, Manon Verwijs-janssen, Patricia Cramers, Adrian C. Begg, Conchita VensAbstract:Evidence for a role of DNA polymerase beta in determining radiosensitivity is conflicting. In vitro assays show an involvement of DNA polymerase beta in single strand break repair and base excision repair of oxidative damages, both products of ionizing radiation. Nevertheless the lack of DNA polymerase beta has been shown to have no effect on radiosensitivity. Here we show that mouse embryonic fibroblasts deficient in DNA polymerase beta are considerably more sensitive to ionizing radiation than wild-type cells, but only when confluent. The inhibitor methoxyamine renders abasic sites refractory to the dRP lyase activity of DNA polymerase beta. Methoxyamine did not significantly change radiosensitivity of wild-type fibroblasts in log phase. However, DNA polymerase beta deficient cells in log phase were radiosensitized by methoxyamine. Alkaline comet assays confirmed repair inhibition of ionizing radiation induced damage by methoxyamine in these cells, indicating both the existence of a polymerase beta-dependent long patch pathway and the involvement of another methoxyamine sensitive process, implying the participation of a second short patch polymerase(s) other than DNA polymerase beta. This is the first evidence of a role for DNA polymerase beta in radiosensitivity in vivo.
Ron A. Bouchard - One of the best experts on this subject based on the ideXlab platform.
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Mechanisms for the Positive Inotropic Effect of a1-Adrenoceptor Stimulation in Rat Cardiac Myocytes
2016Co-Authors: David Fedida, Ron A. BouchardAbstract:exl-Adrenoceptor activation can enhance myocardial contractility, and two possible inotropic mechanisms are an increase in myofilament Ca2 ` sensitivity and action potential prolongation, which can increase net Ca2 ' entry into cells. In adult rat ventricular myocytes (bath Ca2', 1 mM; stimulated at 0.2-0.5 Hz), the drug 4-aminopyridine and the whole-cell voltage clamp have been used to control Ca2 ' entry and differentiate between the two mechanisms. At 22-23°C the specific a!l-adrenoceptor agonist Methoxamine (100,uM) prolonged action potential duration at 50 % repolarization from 55±2 to 81±5 msec, delayed time to peak contraction, and increased shortening amplitude from 5.3±0.6 to 7.8+1,um (n=18). Reduction of the transient outward current and other K ' currents by Methoxamine was the major cause of action potential prolongation in rat myocytes with little change in the L-type calcium current. Block of the transient outward current with 2 mM 4-aminopyridine prolonged action potential duration from 52±6 to 98 ± 12 msec and increased unloaded cell shortening from 2.9±0.4 to 6.6±0.6 p.m (n=4). Subsequently, Methoxamine no longer increased cell shortening, although significant potentiation of twitch amplitude was still seen after a brief rest interval. In voltage-clamp experiments, with 70-500-msec pulses, although membrane currents were reduced, Methoxamine had no positive inotropic effect and reduced cell shortening from 5.3 ±0.7 to 4.97±0.8,um at pulse potentials positive to-40 mV. Similar al-adrenocepto
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mechanisms for the positive inotropic effect of alpha 1 adrenoceptor stimulation in rat cardiac myocytes
Circulation Research, 1992Co-Authors: David Fedida, Ron A. BouchardAbstract:alpha 1-Adrenoceptor activation can enhance myocardial contractility, and two possible inotropic mechanisms are an increase in myofilament Ca2+ sensitivity and action potential prolongation, which can increase net Ca2+ entry into cells. In adult rat ventricular myocytes (bath Ca2+, 1 mM; stimulated at 0.2-0.5 Hz), the drug 4-aminopyridine and the whole-cell voltage clamp have been used to control Ca2+ entry and differentiate between the two mechanisms. At 22-23 degrees C the specific alpha 1-adrenoceptor agonist Methoxamine (100 microM) prolonged action potential duration at 50% repolarization from 55 +/- 2 to 81 +/- 5 msec, delayed time to peak contraction, and increased shortening amplitude from 5.3 +/- 0.6 to 7.8 +/- 1 microns (n = 18). Reduction of the transient outward current and other K+ currents by Methoxamine was the major cause of action potential prolongation in rat myocytes with little change in the L-type calcium current. Block of the transient outward current with 2 mM 4-aminopyridine prolonged action potential duration from 52 +/- 6 to 98 +/- 12 msec and increased unloaded cell shortening from 2.9 +/- 0.4 to 6.6 +/- 0.6 microns (n = 4). Subsequently, Methoxamine no longer increased cell shortening, although significant potentiation of twitch amplitude was still seen after a brief rest interval. In voltage-clamp experiments, with 70-500-msec pulses, although membrane currents were reduced, Methoxamine had no positive inotropic effect and reduced cell shortening from 5.3 +/- 0.7 to 4.97 +/- 0.8 microns at pulse potentials positive to -40 mV. Similar alpha 1-adrenoceptor responses were observed at 35 degrees C during action potential and voltage-clamp experiments, which could be blocked by 10 microM prazosin. In myocytes loaded with the Ca2+ indicator indo-1, alpha 1-adrenoceptor stimulation or 4-aminopyridine both increased cell contraction and intracellular Ca2+ transients by similar amounts. As in unloaded cells, prior exposure to 4-aminopyridine prevented any inotropic effect of Methoxamine without changing the systolic intracellular Ca2+ transient. The results indicated that under our experimental conditions positive inotropy in rat cardiomyocytes on exposure to alpha 1-adrenoceptor agonists was strongly correlated with the action potential prolongation that accompanied K+ current reduction. In addition, modulation of K+ channels could occur independent of changes in contractility and/or [Ca2+]i.
Martin J Kelly - One of the best experts on this subject based on the ideXlab platform.
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the noradrenergic inhibition of an apamin sensitive small conductance ca2 activated k channel in hypothalamic γ aminobutyric acid neurons pharmacology estrogen sensitivity and relevance to the control of the reproductive axis
Journal of Pharmacology and Experimental Therapeutics, 2001Co-Authors: Edward J Wagner, Oline K Ronnekleiv, Martin J KellyAbstract:The present study sought to determine whether small-conductance, Ca2+-activated K+ currents underlie the afterhyperpolarization (AHP) in neurons of the preoptic area (POA), a brain region important in controlling reproduction. We used an ovariectomized, female guinea pig model to test two hypotheses: 1) the current associated with the AHP (IAHP) regulates the firing rate of POA neurons and 2) amine neurotransmitters modulate it in a gonadal steroid-sensitive manner. Intracellular recordings followed by combined histofluorescence/in situ hybridization for glutamic acid decarboxylase, 65-kDa isomer, revealed that POA neurons, including γ-aminobutyric acid (GABA)ergic neurons, exhibited an AHP and spike frequency adaptation. The corresponding IAHP was sensitive to antagonism by CdCl2 (200 μM), apamin (0.3–1 μM), and dequalinium (3 μM). The β-adrenergic receptor agonist isoproterenol inhibited the IAHP in a dose-dependent, timolol-sensitive fashion. In addition, the α1-adrenergic receptor agonist Methoxamine dose dependently inhibited the IAHP in a prazosin-sensitive manner and increased neuronal firing rate. Twenty-four-hour pretreatment with estradiol benzoate (EB; 25 μg, s.c.) markedly potentiated the inhibitory effect of Methoxamine on the IAHP, whereas that for isoproterenol was unaffected. Similarly, bath application of 17β-estradiol (100 nM; 15–20 min) mimicked the effect of EB on the Methoxamine-induced inhibition of the IAHP. Thus, POA GABAergic neurons express an apamin-sensitive channel that mediates, at least in part, the IAHP, and tempers the excitability of these cells. Furthermore, these studies demonstrate that estrogen enhances the α1-adrenergic receptor-mediated inhibition of this current.
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the noradrenergic inhibition of an apamin sensitive small conductance ca2 activated k channel in hypothalamic γ aminobutyric acid neurons pharmacology estrogen sensitivity and relevance to the control of the reproductive axis
Journal of Pharmacology and Experimental Therapeutics, 2001Co-Authors: Edward J Wagner, Oline K Ronnekleiv, Martin J KellyAbstract:The present study sought to determine whether small-conductance, Ca2+-activated K+ currents underlie the afterhyperpolarization (AHP) in neurons of the preoptic area (POA), a brain region important in controlling reproduction. We used an ovariectomized, female guinea pig model to test two hypotheses: 1) the current associated with the AHP (I(AHP)) regulates the firing rate of POA neurons and 2) amine neurotransmitters modulate it in a gonadal steroid-sensitive manner. Intracellular recordings followed by combined histofluorescence/in situ hybridization for glutamic acid decarboxylase, 65-kDa isomer, revealed that POA neurons, including gamma-aminobutyric acid (GABA)ergic neurons, exhibited an AHP and spike frequency adaptation. The corresponding I(AHP) was sensitive to antagonism by CdCl2 (200 microM), apamin (0.3-1 microM), and dequalinium (3 microM). The beta-adrenergic receptor agonist isoproterenol inhibited the I(AHP) in a dose-dependent, timolol-sensitive fashion. In addition, the alpha1-adrenergic receptor agonist Methoxamine dose dependently inhibited the I(AHP) in a prazosin-sensitive manner and increased neuronal firing rate. Twenty-four-hour pretreatment with estradiol benzoate (EB; 25 microg, s.c.) markedly potentiated the inhibitory effect of Methoxamine on the I(AHP), whereas that for isoproterenol was unaffected. Similarly, bath application of 17beta-estradiol (100 nM; 15-20 min) mimicked the effect of EB on the Methoxamine-induced inhibition of the I(AHP). Thus, POA GABAergic neurons express an apamin-sensitive channel that mediates, at least in part, the I(AHP), and tempers the excitability of these cells. Furthermore, these studies demonstrate that estrogen enhances the alpha1-adrenergic receptor-mediated inhibition of this current.
Christie Vermeulen - One of the best experts on this subject based on the ideXlab platform.
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Role for DNA polymerase beta in response to ionizing radiation
Cancer Research, 2007Co-Authors: Christie Vermeulen, Manon Verwijs-janssen, Patricia Cramers, Adrian C. Begg, Conchita VensAbstract:3903 Evidence for a role of DNA polymerase beta in determining radiosensitivity is conflicting. In vitro assays show an involvement of DNA polymerase beta in single strand break repair and base excision repair of oxidative damage, both products of ionizing radiation. Nevertheless the lack of DNA polymerase beta has been shown to have no effect on radiosensitivity. Here we show that mouse embryonic fibroblasts deficient in DNA polymerase beta are considerably more sensitive to ionizing radiation than wild-type cells, but only when confluent. The data indicates that replication associated repair is independent of DNA polymerase beta, and when replication is low, repair of DNA damage induced by ionizing radiation depends on DNA polymerase beta. To further strengthen our hypothesis, we synchronized wild-type and polymerase beta deficient cells with ‘mitotic shake off’ and found that DNA polymerase beta deficient cells are more sensitive to ionizing radiation than wild-type cells in G1 phase of the cell cycle, but radiosensitivity of DNA polymerase beta deficient cells decreased when cells progressed from G1 to S phase. No difference in radiosensitivity between wild-type and polymerase beta deficient cells was observed in S phase, showing that redundant pathways are active in replicating cells only. To characterize these pathways further, we used the inhibitor methoxyamine that renders abasic sites refractory to the dRP lyase activity of DNA polymerase beta. Methoxyamine did not significantly change radiosensitivity of wild-type fibroblasts in log phase. However, DNA polymerase beta deficient cells in log phase were radiosensitized by methoxyamine. Alkaline comet assays confirmed repair inhibition of ionizing radiation induced damage by methoxyamine in these cells, indicating both the existence of a polymerase beta-dependent long patch pathway and the involvement of another methoxyamine sensitive process, implying the participation of a second short patch polymerase(s) other than DNA polymerase beta. This is the first evidence of a role for DNA polymerase beta in radiosensitivity in vivo. To further investigate the possibility of a second short patch pathway, we are currently studying DNA polymerases iota and lambda, both translesion synthesis polymerases which have enzymatic and structural similarities to DNA polymerase beta. Knockdown and overexpression experiments are being performed to reveal the possible contribution of DNA polymerase iota and lambda to single strand break repair and base excision repair after ionizing radiation.
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Role for DNA polymerase beta in response to ionizing radiation
DNA repair, 2006Co-Authors: Christie Vermeulen, Manon Verwijs-janssen, Patricia Cramers, Adrian C. Begg, Conchita VensAbstract:Evidence for a role of DNA polymerase beta in determining radiosensitivity is conflicting. In vitro assays show an involvement of DNA polymerase beta in single strand break repair and base excision repair of oxidative damages, both products of ionizing radiation. Nevertheless the lack of DNA polymerase beta has been shown to have no effect on radiosensitivity. Here we show that mouse embryonic fibroblasts deficient in DNA polymerase beta are considerably more sensitive to ionizing radiation than wild-type cells, but only when confluent. The inhibitor methoxyamine renders abasic sites refractory to the dRP lyase activity of DNA polymerase beta. Methoxyamine did not significantly change radiosensitivity of wild-type fibroblasts in log phase. However, DNA polymerase beta deficient cells in log phase were radiosensitized by methoxyamine. Alkaline comet assays confirmed repair inhibition of ionizing radiation induced damage by methoxyamine in these cells, indicating both the existence of a polymerase beta-dependent long patch pathway and the involvement of another methoxyamine sensitive process, implying the participation of a second short patch polymerase(s) other than DNA polymerase beta. This is the first evidence of a role for DNA polymerase beta in radiosensitivity in vivo.
J R Johnston - One of the best experts on this subject based on the ideXlab platform.
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use of Methoxamine in the resuscitation of epinephrine resistant electromechanical dissociation
Anaesthesia, 2001Co-Authors: M E Mcbrien, D S Breslin, S Atkinson, J R JohnstonAbstract:We describe three cases of electromechanical dissociation under anaesthesia that were unresponsive to doses of intravenous epinephrine given according to current Advanced Life Support guidelines, but which responded immediately to the intravenous administration of the pure α agonist, Methoxamine. We suggest a possible mechanism to explain this finding and review the literature on vasopressor drugs used for cardiopulmonary resuscitation during electromechanical dissociation. An intravenous α agonist, such as Methoxamine 20 mg, should be considered for any case of cardiac arrest secondary to electromechanical dissociation which is unresponsive to epinephrine given according to current guidelines.
