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Horváth B, Szentandrássy N, Dienes C, Kovács ZM, Nánási PP, Chen-Izu Y, Izu LT, Banyasz T. Exploring the Coordination of Cardiac Ion Channels With Action Potential Clamp Technique. Front Physiol 2022; 13:864002. [PMID: 35370800 PMCID: PMC8966222 DOI: 10.3389/fphys.2022.864002] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2022] [Accepted: 02/15/2022] [Indexed: 11/30/2022] Open
Abstract
The patch clamp technique underwent continual advancement and developed numerous variants in cardiac electrophysiology since its introduction in the late 1970s. In the beginning, the capability of the technique was limited to recording one single current from one cell stimulated with a rectangular command pulse. Since that time, the technique has been extended to record multiple currents under various command pulses including action potential. The current review summarizes the development of the patch clamp technique in cardiac electrophysiology with special focus on the potential applications in integrative physiology.
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Affiliation(s)
- Balázs Horváth
- Department of Physiology, University of Debrecen, Debrecen, Hungary
| | - Norbert Szentandrássy
- Department of Physiology, University of Debrecen, Debrecen, Hungary
- Department of Basic Medical Sciences, Faculty of Dentistry, University of Debrecen, Debrecen, Hungary
| | - Csaba Dienes
- Department of Physiology, University of Debrecen, Debrecen, Hungary
| | | | - Péter P. Nánási
- Department of Physiology, University of Debrecen, Debrecen, Hungary
- Department of Basic Medical Sciences, Faculty of Dentistry, University of Debrecen, Debrecen, Hungary
| | - Ye Chen-Izu
- Department of Pharmacology, University of California, Davis, Davis, CA, United States
| | - Leighton T. Izu
- Department of Pharmacology, University of California, Davis, Davis, CA, United States
| | - Tamas Banyasz
- Department of Physiology, University of Debrecen, Debrecen, Hungary
- *Correspondence: Tamas Banyasz,
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Canine Myocytes Represent a Good Model for Human Ventricular Cells Regarding Their Electrophysiological Properties. Pharmaceuticals (Basel) 2021; 14:ph14080748. [PMID: 34451845 PMCID: PMC8398821 DOI: 10.3390/ph14080748] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Revised: 07/18/2021] [Accepted: 07/20/2021] [Indexed: 12/19/2022] Open
Abstract
Due to the limited availability of healthy human ventricular tissues, the most suitable animal model has to be applied for electrophysiological and pharmacological studies. This can be best identified by studying the properties of ion currents shaping the action potential in the frequently used laboratory animals, such as dogs, rabbits, guinea pigs, or rats, and comparing them to those of human cardiomyocytes. The authors of this article with the experience of three decades of electrophysiological studies, performed in mammalian and human ventricular tissues and isolated cardiomyocytes, summarize their results obtained regarding the major canine and human cardiac ion currents. Accordingly, L-type Ca2+ current (ICa), late Na+ current (INa-late), rapid and slow components of the delayed rectifier K+ current (IKr and IKs, respectively), inward rectifier K+ current (IK1), transient outward K+ current (Ito1), and Na+/Ca2+ exchange current (INCX) were characterized and compared. Importantly, many of these measurements were performed using the action potential voltage clamp technique allowing for visualization of the actual current profiles flowing during the ventricular action potential. Densities and shapes of these ion currents, as well as the action potential configuration, were similar in human and canine ventricular cells, except for the density of IK1 and the recovery kinetics of Ito. IK1 displayed a largely four-fold larger density in canine than human myocytes, and Ito recovery from inactivation displayed a somewhat different time course in the two species. On the basis of these results, it is concluded that canine ventricular cells represent a reasonably good model for human myocytes for electrophysiological studies, however, it must be borne in mind that due to their stronger IK1, the repolarization reserve is more pronounced in canine cells, and moderate differences in the frequency-dependent repolarization patterns can also be anticipated.
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Ion current profiles in canine ventricular myocytes obtained by the "onion peeling" technique. J Mol Cell Cardiol 2021; 158:153-162. [PMID: 34089737 DOI: 10.1016/j.yjmcc.2021.05.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Revised: 05/05/2021] [Accepted: 05/21/2021] [Indexed: 02/07/2023]
Abstract
The profiles of ion currents during the cardiac action potential can be visualized by the action potential voltage clamp technique. To obtain multiple ion current data from the same cell, the "onion peeling" technique, based on sequential pharmacological dissection of ion currents, has to be applied. Combination of the two methods allows recording of several ion current profiles from the same myocyte under largely physiological conditions. Using this approach, we have studied the densities and integrals of the major cardiac inward (ICa, INCX, INa-late) and outward (IKr, IKs, IK1) currents in canine ventricular cells and studied the correlation between them. For this purpose, canine ventricular cardiomyocytes were chosen because their electrophysiological properties are similar to those of human ones. Significant positive correlation was observed between the density and integral of ICa and IKr, and positive correlation was found also between the integral of ICa and INCX. No further correlations were detected. The Ca2+-sensitivity of K+ currents was studied by comparing their parameters in the case of normal calcium homeostasis and following blockade of ICa. Out of the three K+ currents studied, only IKs was Ca2+-sensitive. The density and integral of IKs was significantly greater, while its time-to-peak value was shorter at normal Ca2+ cycling than following ICa blockade. No differences were detected for IKr or IK1 in this regard. Present results indicate that the positive correlation between ICa and IKr prominently contribute to the balance between inward and outward fluxes during the action potential plateau in canine myocytes. The results also suggest that the profiles of cardiac ion currents have to be studied under physiological conditions, since their behavior may strongly be influenced by the intracellular Ca2+ homeostasis and the applied membrane potential protocol.
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Glutamate receptors of the A5 region modulate cardiovascular responses evoked from the dorsomedial hypothalamic nucleus and perifornical area. J Physiol Biochem 2018; 74:325-334. [PMID: 29577176 DOI: 10.1007/s13105-018-0623-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Accepted: 03/15/2018] [Indexed: 01/16/2023]
Abstract
To assess the possible function of glutamate in the interaction between the dorsomedial hypothalamic nucleus-perifornical area (DMH-PeF) and the A5 pontine region (A5), cardiovascular and respiratory changes were studied in response to electrical stimulation of the DMH-PeF (1 ms pulses, 30-50 μA given at 100 Hz for 5 s) before and after the microinjection of kynurenic acid (non-specific glutamate receptor antagonist; 50 nl, 5 nmol), MK-801 (NMDA receptor antagonist; 50 nl, 50 nmol), CNQX (non-NMDA receptor antagonist; 50 nl, 50 nmol) or MCPG (metabotropic glutamate receptor antagonist; 50 nl, 5 nmol) within the A5 region. DMH-PeF electrical stimulation elicited a pressor (p < 0.001) and tachycardic response (p < 0.001) which was accompanied by an inspiratory facilitation characterised by an increase in respiratory rate (p < 0.001) due to a decrease in expiratory time (p < 0.01). Kynurenic acid within the A5 region decreased the tachycardia (p < 0.001) and the intensity of the blood pressure response (p < 0.001) to DMH-PeF stimulation. After the microinjection of MK-801 and CNQX into the A5 region, the magnitude of the tachycardia and the pressor response were decreased (p < 0.05 and p < 0.01; p < 0.001 and p < 0.05, respectively). After MCPG microinjection into the A5 region, a decrease in the tachycardia (p < 0.001) with no changes in the pressor response was observed during DMH-PeF stimulation. The respiratory response elicited by DMH-PeF stimulation was not changed after the microinjection of kynurenic acid, MK-801, CNQX or MCPG within the A5 region. These results suggest that A5 region glutamate receptors play a role in the cardiovascular response elicited from the DMH-PeF. The possible mechanisms involved in these interactions are discussed.
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Yuki H, Utsunomiya D, Shiraishi S, Takashio S, Sakamoto F, Tsuda N, Oda S, Kidoh M, Nakaura T, Tsujita K, Yamashita Y. Correlation of left ventricular dyssynchrony on gated myocardial perfusion SPECT analysis with extent of late gadolinium enhancement on cardiac magnetic resonance imaging in hypertrophic cardiomyopathy. Heart Vessels 2017; 33:623-629. [DOI: 10.1007/s00380-017-1104-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Accepted: 12/08/2017] [Indexed: 10/18/2022]
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Activation of the Ca 2+-sensing receptors increases currents through inward rectifier K + channels via activation of phosphatidylinositol 4-kinase. Pflugers Arch 2016; 468:1931-1943. [PMID: 27838849 PMCID: PMC5138266 DOI: 10.1007/s00424-016-1901-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2016] [Revised: 10/26/2016] [Accepted: 11/06/2016] [Indexed: 10/25/2022]
Abstract
Inward rectifier K+ channels are important for maintaining normal electrical function in many cell types. The proper function of these channels requires the presence of membrane phosphoinositide 4,5-bisphosphate (PIP2). Stimulation of the Ca2+-sensing receptor CaR, a pleiotropic G protein-coupled receptor, activates both Gq/11, which decreases PIP2, and phosphatidylinositol 4-kinase (PI-4-K), which, conversely, increases PIP2. How membrane PIP2 levels are regulated by CaR activation and whether these changes modulate inward rectifier K+ are unknown. In this study, we found that activation of CaR by the allosteric agonist, NPSR568, increased inward rectifier K+ current (I K1) in guinea pig ventricular myocytes and currents mediated by Kir2.1 channels exogenously expressed in HEK293T cells with a similar sensitivity. Moreover, using the fluorescent PIP2 reporter tubby-R332H-cYFP to monitor PIP2 levels, we found that CaR activation in HEK293T cells increased membrane PIP2 concentrations. Pharmacological studies showed that both phospholipase C (PLC) and PI-4-K are activated by CaR stimulation with the latter played a dominant role in regulating membrane PIP2 and, thus, Kir currents. These results provide the first direct evidence that CaR activation upregulates currents through inward rectifier K+ channels by accelerating PIP2 synthesis. The regulation of I K1 plays a critical role in the stability of the electrical properties of many excitable cells, including cardiac myocytes and neurons. Further, synthetic allosteric modulators that increase CaR activity have been used to treat hyperparathyroidism, and negative CaR modulators are of potential importance in the treatment of osteoporosis. Thus, our results provide further insight into the roles played by CaR in the cardiovascular system and are potentially valuable for heart disease treatment and drug safety.
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Ramos-Franco J, Aguilar-Sanchez Y, Escobar AL. Intact Heart Loose Patch Photolysis Reveals Ionic Current Kinetics During Ventricular Action Potentials. Circ Res 2015; 118:203-15. [PMID: 26565013 DOI: 10.1161/circresaha.115.307399] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Accepted: 11/12/2015] [Indexed: 12/16/2022]
Abstract
RATIONALE Assessing the underlying ionic currents during a triggered action potential (AP) in intact perfused hearts offers the opportunity to link molecular mechanisms with pathophysiological problems in cardiovascular research. The developed loose patch photolysis technique can provide striking new insights into cardiac function at the whole heart level during health and disease. OBJECTIVE To measure transmembrane ionic currents during an AP to determine how and when surface Ca(2+) influx that triggers Ca(2+)-induced Ca(2+) release occurs and how Ca(2+)-activated conductances can contribute to the genesis of AP phase 2. METHODS AND RESULTS Loose patch photolysis allows the measurement of transmembrane ionic currents in intact hearts. During a triggered AP, a voltage-dependent Ca(2+) conductance was fractionally activated (dis-inhibited) by rapidly photo-degrading nifedipine, the Ca(2+) channel blocker. The ionic currents during a mouse ventricular AP showed a fast early component and a slower late component. Pharmacological studies established that the molecular basis underlying the early component was driven by an influx of Ca(2+) through the L-type channel, CaV 1.2. The late component was identified as an Na(+)-Ca(2+) exchanger current mediated by Ca(2+) released from the sarcoplasmic reticulum. CONCLUSIONS The novel loose patch photolysis technique allowed the dissection of transmembrane ionic currents in the intact heart. We were able to determine that during an AP, L-type Ca(2+) current contributes to phase 1, whereas Na(+)-Ca(2+) exchanger contributes to phase 2. In addition, loose patch photolysis revealed that the influx of Ca(2+) through L-type Ca(2+) channels terminates because of voltage-dependent deactivation and not by Ca(2+)-dependent inactivation, as commonly believed.
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Affiliation(s)
- Josefina Ramos-Franco
- From the Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL (J.R.-F.); and Quantitative Systems Biology Program, School of Natural Sciences (Y.A.-S.) and Biological Engineering and Small Scale Technologies Program, School of Engineering (A.L.E.), University of California, Merced, CA
| | - Yuriana Aguilar-Sanchez
- From the Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL (J.R.-F.); and Quantitative Systems Biology Program, School of Natural Sciences (Y.A.-S.) and Biological Engineering and Small Scale Technologies Program, School of Engineering (A.L.E.), University of California, Merced, CA
| | - Ariel L Escobar
- From the Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL (J.R.-F.); and Quantitative Systems Biology Program, School of Natural Sciences (Y.A.-S.) and Biological Engineering and Small Scale Technologies Program, School of Engineering (A.L.E.), University of California, Merced, CA.
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Hummel YM, Wilde AA, Voors AA, Bugatti S, Hillege HL, van den Berg MP. Ventricular dysfunction in a family with long QT syndrome type 3. ACTA ACUST UNITED AC 2013; 15:1516-21. [DOI: 10.1093/europace/eut101] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Szentandrássy N, Farkas V, Bárándi L, Hegyi B, Ruzsnavszky F, Horváth B, Bányász T, Magyar J, Márton I, Nánási PP. Role of action potential configuration and the contribution of C²⁺a and K⁺ currents to isoprenaline-induced changes in canine ventricular cells. Br J Pharmacol 2013; 167:599-611. [PMID: 22563726 DOI: 10.1111/j.1476-5381.2012.02015.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
BACKGROUND AND PURPOSE Although isoprenaline (ISO) is known to activate several ion currents in mammalian myocardium, little is known about the role of action potential morphology in the ISO-induced changes in ion currents. Therefore, the effects of ISO on action potential configuration, L-type Ca²⁺ current (I(Ca)), slow delayed rectifier K⁺ current (I(Ks)) and fast delayed rectifier K⁺ current (I(Kr)) were studied and compared in a frequency-dependent manner using canine isolated ventricular myocytes from various transmural locations. EXPERIMENTAL APPROACH Action potentials were recorded with conventional sharp microelectrodes; ion currents were measured using conventional and action potential voltage clamp techniques. KEY RESULTS In myocytes displaying a spike-and-dome action potential configuration (epicardial and midmyocardial cells), ISO caused reversible shortening of action potentials accompanied by elevation of the plateau. ISO-induced action potential shortening was absent in endocardial cells and in myocytes pretreated with 4-aminopyridine. Application of the I(Kr) blocker E-4031 failed to modify the ISO effect, while action potentials were lengthened by ISO in the presence of the I(Ks) blocker HMR-1556. Both action potential shortening and elevation of the plateau were prevented by pretreatment with the I(Ca) blocker nisoldipine. Action potential voltage clamp experiments revealed a prominent slowly inactivating I(Ca) followed by a rise in I(Ks) , both currents increased with increasing the cycle length. CONCLUSIONS AND IMPLICATIONS The effect of ISO in canine ventricular cells depends critically on action potential configuration, and the ISO-induced activation of I(Ks) - but not I(Kr) - may be responsible for the observed shortening of action potentials.
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Chang HK, Shieh RC. Voltage-dependent inhibition of outward Kir2.1 currents by extracellular spermine. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:765-75. [PMID: 22948070 DOI: 10.1016/j.bbamem.2012.08.016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2012] [Revised: 08/17/2012] [Accepted: 08/20/2012] [Indexed: 10/27/2022]
Abstract
Outward currents through inward rectifier Kir2.1 channels play crucial roles in controlling the electrical properties of excitable cells. Extracellular monovalent and divalent cations have been shown to reduce outward K(+) conductance. In the present study, we examined whether spermine, with four positive charges, also inhibits outward Kir2.1 currents. We found that extracellular spermine inhibits steady-state outward Kir2.1 currents, an effect that increases as the voltage becomes more depolarizing, similar to that observed for intracellular spermine. However, several lines of evidence suggest that extracellular spermine does not inhibit outward currents by entering the cytoplasmic pore. Site-directed mutagenesis studies support that extracellular spermine directly interacts with the extracellular domain. In addition, we found that the voltage-dependent decay of outward Kir2.1 currents was necessary for inhibition by extracellular spermine. Further, a region at or near the selectivity filter and the cytoplasmic pore are involved in the voltage-dependent decay and thus in the inhibition of outward currents by extracellular spermine. Taken together, the data suggest that extracellular spermine bound to the mouth of the extracellular pore may induce an allosteric effect on voltage-dependent decay of outward currents, a process in which a region in the vicinity of the selectivity filter and cytoplasmic pore are involved. This study reveals that the extracellular pore domain, the selectivity filter and the cytoplasmic pore are in communication and this coupling is involved in modulating K(+) conduction in the Kir2.1 channel.
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Affiliation(s)
- Hsueh-Kai Chang
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan, ROC
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Gauthier LD, Greenstein JL, Winslow RL. Toward an integrative computational model of the Guinea pig cardiac myocyte. Front Physiol 2012; 3:244. [PMID: 22783206 PMCID: PMC3389778 DOI: 10.3389/fphys.2012.00244] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2012] [Accepted: 06/14/2012] [Indexed: 11/22/2022] Open
Abstract
The local control theory of excitation-contraction (EC) coupling asserts that regulation of calcium (Ca2+) release occurs at the nanodomain level, where openings of single L-type Ca2+ channels (LCCs) trigger openings of small clusters of ryanodine receptors (RyRs) co-localized within the dyad. A consequence of local control is that the whole-cell Ca2+ transient is a smooth continuous function of influx of Ca2+ through LCCs. While this so-called graded release property has been known for some time, its functional importance to the integrated behavior of the cardiac ventricular myocyte has not been fully appreciated. We previously formulated a biophysically based model, in which LCCs and RyRs interact via a coarse-grained representation of the dyadic space. The model captures key features of local control using a low-dimensional system of ordinary differential equations. Voltage-dependent gain and graded Ca2+ release are emergent properties of this model by virtue of the fact that model formulation is closely based on the sub-cellular basis of local control. In this current work, we have incorporated this graded release model into a prior model of guinea pig ventricular myocyte electrophysiology, metabolism, and isometric force production. The resulting integrative model predicts the experimentally observed causal relationship between action potential (AP) shape and timing of Ca2+ and force transients, a relationship that is not explained by models lacking the graded release property. Model results suggest that even relatively subtle changes in AP morphology that may result, for example, from remodeling of membrane transporter expression in disease or spatial variation in cell properties, may have major impact on the temporal waveform of Ca2+ transients, thus influencing tissue level electromechanical function.
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Affiliation(s)
- Laura Doyle Gauthier
- Department of Biomedical Engineering, Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering Baltimore, MD, USA
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Morgado M, Cairrão E, Santos-Silva AJ, Verde I. Cyclic nucleotide-dependent relaxation pathways in vascular smooth muscle. Cell Mol Life Sci 2012; 69:247-66. [PMID: 21947498 PMCID: PMC11115151 DOI: 10.1007/s00018-011-0815-2] [Citation(s) in RCA: 135] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2011] [Revised: 08/21/2011] [Accepted: 08/23/2011] [Indexed: 02/07/2023]
Abstract
Vascular smooth muscle tone is controlled by a balance between the cellular signaling pathways that mediate the generation of force (vasoconstriction) and release of force (vasodilation). The initiation of force is associated with increases in intracellular calcium concentrations, activation of myosin light-chain kinase, increases in the phosphorylation of the regulatory myosin light chains, and actin-myosin crossbridge cycling. There are, however, several signaling pathways modulating Ca(2+) mobilization and Ca(2+) sensitivity of the contractile machinery that secondarily regulate the contractile response of vascular smooth muscle to receptor agonists. Among these regulatory mechanisms involved in the physiological regulation of vascular tone are the cyclic nucleotides (cAMP and cGMP), which are considered the main messengers that mediate vasodilation under physiological conditions. At least four distinct mechanisms are currently thought to be involved in the vasodilator effect of cyclic nucleotides and their dependent protein kinases: (1) the decrease in cytosolic calcium concentration ([Ca(2+)]c), (2) the hyperpolarization of the smooth muscle cell membrane potential, (3) the reduction in the sensitivity of the contractile machinery by decreasing the [Ca(2+)]c sensitivity of myosin light-chain phosphorylation, and (4) the reduction in the sensitivity of the contractile machinery by uncoupling contraction from myosin light-chain phosphorylation. This review focuses on each of these mechanisms involved in cyclic nucleotide-dependent relaxation of vascular smooth muscle under physiological conditions.
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Affiliation(s)
- Manuel Morgado
- Health Sciences Research Centre (CICS-UBI), University of Beira Interior, Av. Infante D. Henrique, 6200-506 Covilhã, Portugal
| | - Elisa Cairrão
- Health Sciences Research Centre (CICS-UBI), University of Beira Interior, Av. Infante D. Henrique, 6200-506 Covilhã, Portugal
| | - António José Santos-Silva
- Health Sciences Research Centre (CICS-UBI), University of Beira Interior, Av. Infante D. Henrique, 6200-506 Covilhã, Portugal
| | - Ignacio Verde
- Health Sciences Research Centre (CICS-UBI), University of Beira Interior, Av. Infante D. Henrique, 6200-506 Covilhã, Portugal
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Rigby JR, Poelzing S. A novel frequency analysis method for assessing K(ir)2.1 and Na (v)1.5 currents. Ann Biomed Eng 2011; 40:946-54. [PMID: 22052157 PMCID: PMC3310982 DOI: 10.1007/s10439-011-0460-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2011] [Accepted: 10/28/2011] [Indexed: 11/30/2022]
Abstract
Voltage clamping is an important tool for measuring individual currents from an electrically active cell. However, it is difficult to isolate individual currents without pharmacological or voltage inhibition. Herein, we present a technique that involves inserting a noise function into a standard voltage step protocol, which allows one to characterize the unique frequency response of an ion channel at different step potentials. Specifically, we compute the fast Fourier transform for a family of current traces at different step potentials for the inward rectifying potassium channel, Kir2.1, and the channel encoding the cardiac fast sodium current, Nav1.5. Each individual frequency magnitude, as a function of voltage step, is correlated to the peak current produced by each channel. The correlation coefficient vs. frequency relationship reveals that these two channels are associated with some unique frequencies with high absolute correlation. The individual IV relationship can then be recreated using only the unique frequencies with magnitudes of high absolute correlation. Thus, this study demonstrates that ion channels may exhibit unique frequency responses.
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Affiliation(s)
- J. R. Rigby
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, 95 South 2000 East, Salt Lake City, UT 84112 USA
- Department of Bioengineering, University of Utah, 72 South Central Campus Drive, Room 2750, Salt Lake City, UT 84112 USA
| | - S. Poelzing
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, 95 South 2000 East, Salt Lake City, UT 84112 USA
- Department of Bioengineering, University of Utah, 72 South Central Campus Drive, Room 2750, Salt Lake City, UT 84112 USA
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Akbar N, Mohamed T, Whitehead D, Azzawi M. Biocompatibility of amorphous silica nanoparticles: Size and charge effect on vascular function, in vitro. Biotechnol Appl Biochem 2011; 58:353-62. [PMID: 21995538 DOI: 10.1002/bab.46] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2011] [Accepted: 08/01/2011] [Indexed: 12/21/2022]
Abstract
Synthetic amorphous silica is gaining popularity as the material of choice in the fabrication of nanoparticles for use in imaging diagnostics, medical therapeutics, and tissue engineering because of its biocompatible nature. However, recent evidence suggests that silica nanoparticles (SiNPs) show a concentration- and size-dependent toxic effect that is cell specific. We investigated the direct influence of SiNP uptake on the vasodilator responses of rat aortic vessels, in vitro, using fabricated SiNPs of defined size (97 ± 7.60 and 197 ± 7.50 nm) and charge (positive and nonmodified). Dilator responses to cumulative doses of endothelial-dependent [acetylcholine (Ach); 0.01 µM-1.0 mM] and endothelial-independent (sodium nitroprusside; 0.01-10 µM) agonists were determined before and 30 Min after incubation in SiNPs (at 1.1 × 10(11) nanoparticles/mL). Acute exposure to SiNPs led to their rapid uptake by the lining endothelial cells (as verified by transmission electron microscopy). SiNP uptake had no significant influence on dilator responses, although a greater degree of attenuation was evident after uptake of the 100 nm and positively charged SiNPs (significant at the highest 1.0 mM Ach concentration between positive and nonmodified 200 nm SiNPs; P < 0.05). In summary, our findings suggest that SiNP surface interactions, rather than mass, affect vasodilator function of aortic vessels.
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Affiliation(s)
- Naveed Akbar
- The School of Healthcare Science, Faculty of Science and Engineering, Manchester Metropolitan University, Manchester, UK
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Profile of L-type Ca(2+) current and Na(+)/Ca(2+) exchange current during cardiac action potential in ventricular myocytes. Heart Rhythm 2011; 9:134-42. [PMID: 21884673 DOI: 10.1016/j.hrthm.2011.08.029] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2011] [Accepted: 08/28/2011] [Indexed: 11/17/2022]
Abstract
OBJECTIVE The L-type Ca(2+) current (I(Ca,L)) and the Na(+)/Ca(2+) exchange current (I(NCX)) are major inward currents that shape the cardiac action potential (AP). Previously, the profile of these currents during the AP was determined from voltage-clamp experiments that used Ca(2+) buffer. In this study, we aimed to obtain direct experimental measurement of these currents during cardiac AP with Ca(2+) cycling. METHOD A newly developed AP-clamp sequential dissection method was used to record ionic currents in guinea pig ventricular myocytes under a triad of conditions: using the cell's own AP as the voltage command, using internal and external solutions that mimic the cell's ionic composition, and, importantly, not using any exogenous Ca(2+) buffer. RESULTS The nifedipine-sensitive current (I(NIFE)), which is composed of I(Ca,L) and I(NCX), revealed hitherto unreported features during the AP with Ca(2+) cycling in the cell. We identified 2 peaks in the current profile followed by a long residual current extending beyond the AP, coinciding with a residual depolarization. The second peak and the residual current become apparent only when Ca(2+) is not buffered. Pharmacological dissection of I(NIFE) by using SEA0400 shows that I(Ca,L) is dominant during phases 1 and 2 whereas I(NCX) contributes significantly to the inward current during phases 3 and 4 of the AP. CONCLUSION These data provide the first direct experimental visualization of I(Ca,L) and I(NCX) during cardiac the AP and Ca(2+) cycle. The residual current reported here can serve as a potential substrate for afterdepolarizations when increased under pathologic conditions.
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Fike CD, Aschner JL, Slaughter JC, Kaplowitz MR, Zhang Y, Pfister SL. Pulmonary arterial responses to reactive oxygen species are altered in newborn piglets with chronic hypoxia-induced pulmonary hypertension. Pediatr Res 2011; 70:136-41. [PMID: 21516056 PMCID: PMC3131458 DOI: 10.1203/pdr.0b013e3182207ce7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Reactive oxygen species (ROS) have been implicated in the pathogenesis of pulmonary hypertension. ROS might mediate vascular responses, at least in part, by stimulating prostanoid production. Our goals were to determine whether the effect of ROS on vascular tone is altered in resistance pulmonary arteries (PRAs) of newborn piglets with chronic hypoxia-induced pulmonary hypertension and the role, if any, of prostanoids in ROS-mediated responses. In cannulated, pressurized PRA, ROS generated by xanthine (X) plus xanthine oxidase (XO) had minimal effect on vascular tone in control piglets but caused significant vasoconstriction in hypoxic piglets. Both cyclooxygenase inhibition with indomethacin and thromboxane synthase inhibition with dazoxiben significantly blunted constriction to X+XO in hypoxic PRA. X+XO increased prostacyclin production (70 ± 8%) by a greater degree than thromboxane production (50 ± 6%) in control PRA; this was not the case in hypoxic PRA where the increases in prostacyclin and thromboxane production were not statistically different (78 ± 13% versus 216 ± 93%, respectively). Thromboxane synthase expression was increased in PRA from hypoxic piglets, whereas prostacyclin synthase expression was similar in PRA from hypoxic and control piglets. Under conditions of chronic hypoxia, altered vascular responses to ROS may contribute to pulmonary hypertension by a mechanism that involves the prostanoid vasoconstrictor, thromboxane.
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Affiliation(s)
- Candice D Fike
- Department of Pediatrics, Vanderbilt University School of Medicine and Monroe Carell Jr. Children's Hospital at Vanderbilt, Nashville, Tennessee 37232, USA.
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17
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Prostaglandin E 1protects blood cell filterability from oxygen free radical-induced injury. Int J Angiol 2011. [DOI: 10.1007/bf02014922] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
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18
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Torres NS, Larbig R, Rock A, Goldhaber JI, Bridge JHB. Na+ currents are required for efficient excitation-contraction coupling in rabbit ventricular myocytes: a possible contribution of neuronal Na+ channels. J Physiol 2011; 588:4249-60. [PMID: 20837647 DOI: 10.1113/jphysiol.2010.194688] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Ca2+ transients were activated in rabbit ventricular cells by a sequence of action potential shaped voltage clamps. After activating a series of control transients, Na+ currents (INa) were inactivated with a ramp from -80 to -40 mV (1.5 s) prior to the action potential clamp. The transients were detected with the calcium indicator Fluo-4 and an epifluorescence system. With zero Na+ in the pipette INa inactivation produced a decline in the SR Ca2+ release flux (measured as the maximum rate of rise of the transient) of 27 ± 4% (n = 9, P < 0.001) and a peak amplitude reduction of 10 ± 3% (n = 9, P < 0.05). With 5 mm Na+ in the pipette the reduction in release flux was greater (34 ± 4%, n = 4, P < 0.05). The ramp effectively inactivates INa without changing ICa, and there was no significant change in the transmembrane Ca2+ flux after the inactivation of INa. We next evoked action potentials under current clamp. TTX at 100 nm, which selectively blocks neuronal isoforms of Na+ channels, produced a decline in SR Ca2+ release flux of 35 ± 3% (n = 6, P < 0.001) and transient amplitude of 12 ± 2% (n = 6, P < 0.05). This effect was similar to the effect of INa inactivation on release flux. We conclude that a TTX-sensitive INa is essential for efficient triggering of SR Ca2+ release. We propose that neuronal Na+ channels residing within couplons activate sufficient reverse Na+-Ca2+ exchanger (NCX) to prime the junctional cleft with Ca2+. The results can be explained if non-linearities in excitation-contraction coupling mechanisms modify the coupling fidelity of ICa, which is known to be low at positive potentials.
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Affiliation(s)
- Natalia S Torres
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, UT 84112-5000, USA
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Abstract
Cyclic guanosine 3', 5'-monophosphate (cGMP) plays an integral role in the control of vascular function. Generated from guanylate cyclases in response to the endogenous ligands, nitric oxide (NO) and natriuretic peptides (NPs), cGMP influences a number of vascular cell types and regulates vasomotor tone, endothelial permeability, cell growth and differentiation, as well as platelet and blood cell interactions. Reciprocal regulation of the NO-cGMP and NP-cGMP pathways is evident in the vasculature such that one cGMP generating system may compensate for the dysfunction of the other. Indeed, aberrant cGMP production and/or signalling accompanies many vascular disorders such as hypertension, atherosclerosis, coronary artery disease and diabetic complications. This chapter highlights the main vascular functions of cGMP, its role in disease and the resulting current and potential therapeutic applications. With respect to pulmonary hypertension, heart failure and erectile dysfunction, as well as cGMP signal transduction, the reader is specifically referred to other dedicated chapters.
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Affiliation(s)
- Barbara Kemp-Harper
- Department of Pharmacology, Monash University, Melbourne (Clayton), VIC, 3800, Australia.
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20
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Haugaa KH, Edvardsen T, Leren TP, Gran JM, Smiseth OA, Amlie JP. Left ventricular mechanical dispersion by tissue Doppler imaging: a novel approach for identifying high-risk individuals with long QT syndrome. Eur Heart J 2008; 30:330-7. [PMID: 18940888 PMCID: PMC2639143 DOI: 10.1093/eurheartj/ehn466] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Aims The aim of this study was to investigate whether prolonged and dispersed myocardial contraction duration assessed by tissue Doppler imaging (TDI) may serve as risk markers for cardiac events (documented arrhythmia, syncope, and cardiac arrest) in patients with long QT syndrome (LQTS). Methods and results Seventy-three patients with genetically confirmed LQTS (nine double- and 33 single-mutation carriers with previous cardiac events and 31 single-mutation carriers without events) were studied. Myocardial contraction duration was prolonged in each group of LQTS patients compared with 20 healthy controls (P < 0.001). Contraction duration was longer in single-mutation carriers with previous cardiac events compared with those without (0.46 ± 0.06 vs. 0.40 ± 0.06 s, P = 0.001). Prolonged contraction duration could better identify cardiac events compared with corrected QT (QTc) interval in single-mutation carriers [area under curve by receiver-operating characteristic analysis 0.77 [95% confidence interval (95% CI) 0.65–0.89] vs. 0.66 (95% CI 0.52–0.79)]. Dispersion of contraction was more pronounced in single-mutation carriers with cardiac events compared with those without (0.048 ± 0.018 vs. 0.031 ± 0.019 s, P = 0.001). Conclusion Dispersion of myocardial contraction assessed by TDI was increased in LQTS patients. Prolonged contraction duration was superior to QTc for risk assessment. These new methods can easily be implemented in clinical routine and may improve clinical management of LQTS patients.
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Affiliation(s)
- Kristina Hermann Haugaa
- Department of Cardiology, Rikshospitalet University Hospital, University of Oslo, N-0027 Oslo, Norway
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21
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García-Redondo AB, Briones AM, Beltrán AE, Alonso MJ, Simonsen U, Salaices M. Hypertension increases contractile responses to hydrogen peroxide in resistance arteries through increased thromboxane A2, Ca2+, and superoxide anion levels. J Pharmacol Exp Ther 2008; 328:19-27. [PMID: 18818375 DOI: 10.1124/jpet.108.144295] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study investigated the mechanisms underlying the response to hydrogen peroxide (H(2)O(2)) in mesenteric resistance arteries from spontaneously hypertensive rats (SHRs) and normotensive Wistar Kyoto (WKY) rats. Arteries were mounted in microvascular myographs for isometric tension recording and for simultaneous measurements of intracellular Ca(2+) concentration ([Ca(2+)](i)), superoxide anion (O(2)(.)) production was evaluated by dihydroethidium fluorescence and confocal microscopy, and thromboxane A(2) (TXA(2)) production was evaluated by enzyme immunoassay. H(2)O(2) (1-100 microM) induced biphasic responses characterized by a transient endothelium-dependent contraction followed by relaxation. Simultaneous measurements of tension and Ca(2+) showed a greater effect of H(2)O(2) in arteries from hypertensive than normotensive rats. The cyclooxygenase (cox) inhibitor, indomethacin [1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1-H-indole-3-acetic acid] (1 microM); the COX-1 inhibitor, SC-58560 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethyl pyrazole] (1 microM); the thromboxane (TXA(2)) synthase inhibitor, furegrelate [5-(3-pyridinylmethyl)-2-benzofurancarboxylic acid, sodium salt] (10 microM); and the TXA(2)/prostaglandin H(2) receptor antagonist, SQ 29,548 ([1S-[1.alpha.,2.alpha.(Z),3.alpha.,4.alpha.]]-7-[3-[[2-[(phenylamino) carbonyl] hydrazino] methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid)) (1 microM) abolished H(2)O(2) contraction in arteries from WKY rats but only reduced it in SHRs. The O(2)(.) scavenger, tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt) (1 mM), and the NADPH oxidase inhibitor, apocynin (4'-hydroxy-3'-methoxyacetophenone) (0.3 mM), decreased H(2)O(2) contraction in arteries from SHRs but not in WKY rats. H(2)O(2) induced TXA(2) and O(2)(.) production that was greater in SHRs than in WKY rats. The TXA(2) analog, U46619 [9,11-di-deoxy-11 alpha,9 alpha-epoxymethano prostaglandin F(2 alpha) (0.1 nM-1 microM)], also increased O(2)(.) production in SHR vessels. H(2)O(2)-induced TXA(2) production was decreased by SC-58560. H(2)O(2)-induced O(2)(.) production was decreased by tiron, apocynin, and SQ 29,548. In conclusion, the enhanced H(2)O(2) contraction in resistance arteries from SHRs seems to be mediated by increased TXA(2) release from COX-1 followed by elevations in vascular smooth muscle [Ca(2+)](i) levels and O(2)(.) production. This reveals a new mechanism of oxidative stress-induced vascular damage in hypertension.
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Affiliation(s)
- Ana Belén García-Redondo
- Departamento de Farmacología, Facultad de Medicina, Universidad Autónoma de Madrid, C/Arzobispo Morcillo 4, 28029 Madrid, Spain
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Sabetkar M, Low SY, Bradley NJ, Jacobs M, Naseem KM, Richard Bruckdorfer K. The nitration of platelet vasodilator stimulated phosphoprotein following exposure to low concentrations of hydrogen peroxide. Platelets 2008; 19:282-92. [PMID: 18569864 DOI: 10.1080/09537100801915142] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Hydrogen peroxide (H2O2) at biologically relevant concentrations acts as a signaling molecule. We have shown previously that H2O2 acts synergistically with nitric oxide (NO) to inhibit platelet aggregation. We found that this synergism may be associated with the increased serine phosphorylation of vasodilator-sensitive phosphoprotein (VASP) by H2O2. In this study we demonstrate that H2O2 in the absence of NO or exogenous haem- containing proteins induces nitration of plateletVASP and other unidentified proteins by a mechanism that may involve the formation of peroxynitrite. The nitration was NO-dependent, but independent of oxidative stress and guanylyl cyclcase. The flavanoid epigallocatechin gallate (ECGC) completely suppressed nitration and was also shown to inhibit partially platelet activation by other agonists. Importantly, protein nitration was reversible, or at least the nitrated tyrosine residues are converted to a form not recognized by anti-nitrotyrosine antibodies. The loss of nitrated VASP was still evident in the presence of membrane permeable protease inhibitors. In conclusion, as H2O2 can inhibit platelet function, the nitration of VASP, a protein critical for actin cytoskeletal rearrangement, may represent a novel mechanism important in the regulation of platelets shape change leading to inhibition of platelets aggregation and the formation of blood clot.
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Contribution of L-type Ca2+ channels to early afterdepolarizations induced by I Kr and I Ks channel suppression in guinea pig ventricular myocytes. J Membr Biol 2008; 222:151-66. [PMID: 18566732 DOI: 10.1007/s00232-008-9113-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2008] [Accepted: 05/16/2008] [Indexed: 10/21/2022]
Abstract
Early afterdepolarizations (EADs) induced by suppression of cardiac delayed rectifier I (Kr) and/or I (Ks) channels cause fatal ventricular tachyarrhythmias. In guinea pig ventricular myocytes, partial block of one of the channels with complete block of the other reproducibly induced EADs. Complete block of both I (Kr) and I (Ks) channels depolarized the take-off potential and reduced the amplitude of EADs, which in some cases were not clearly separated from the preceding action potentials. A selective L-type Ca(2+) (I (Ca,L)) channel blocker, nifedipine, effectively suppressed EADs at submicromolar concentrations. As examined with the action potential-clamp method, I (Ca,L) channels mediated inward currents with a spike and dome shape during action potentials. I (Ca,L) currents decayed mainly due to inactivation in phase 2 and deactivation in phase 3 repolarization. When EADs were induced by complete block of I (Kr) channels with partial block of I (Ks) channels, repolarization of the action potential prior to EAD take-off failed to increase I (K1) currents and thus failed to completely deactivate I (Ca,L) channels, which reactivated and mediated inward currents during EADs. When both I (Kr) and I (Ks) channels were completely blocked, I (Ca,L) channels were not deactivated and mediated sustained inward currents until the end of EADs. Under this condition, the recovery and reactivation of I (Ca,L) channels were absent before EADs. Therefore, an essential mechanism underlying EADs caused by suppression of the delayed rectifiers is the failure to completely deactivate I (Ca,L) channels.
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24
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Loss of A5 noradrenergic neurons in multiple system atrophy. Acta Neuropathol 2008; 115:629-34. [PMID: 18297292 DOI: 10.1007/s00401-008-0351-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2007] [Revised: 02/01/2008] [Accepted: 02/07/2008] [Indexed: 10/22/2022]
Abstract
The A5 noradrenergic group of the pons projects on the medulla and spinal cord and contributes to control of sympathetic activity and respiration. Because these functions are affected in multiple system atrophy (MSA), we sought to determine whether there was involvement of A5 neurons in this disorder. We counted tyrosine-hydroxylase (TH) immunoreactive neurons in the A5 area and locus ceruleus in the pons obtained from six patients with clinical and neuropathological diagnoses of MSA and six age-matched controls using stereological methods. There was a severe loss of A5 neurons in MSA (total cell number 3,215 +/- 258 in controls and 321 +/- 62 in MSA, P < 0.001). The severity of cell loss was comparable to that of locus ceruleus neurons in these cases. Our results indicate that A5 neurons are severely affected in MSA and this may contribute to some of the manifestations of this synucleinopathy.
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25
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Bányász T, Magyar J, Szentandrássy N, Horváth B, Birinyi P, Szentmiklósi J, Nánási PP. Action potential clamp fingerprints of K+ currents in canine cardiomyocytes: their role in ventricular repolarization. Acta Physiol (Oxf) 2007; 190:189-98. [PMID: 17394574 DOI: 10.1111/j.1748-1716.2007.01674.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
AIM The aim of the present study was to give a parametric description of the most important K(+) currents flowing during canine ventricular action potential. METHODS Inward rectifier K(+) current (I(K1)), rapid delayed rectifier K(+) current (I(Kr)), and transient outward K(+) current (I(to)) were dissected under action potential clamp conditions using BaCl(2), E-4031, and 4-aminopyridine, respectively. RESULTS The maximum amplitude of I(to) was 3.0 +/- 0.23 pA/pF and its integral was 29.7 +/- 2.5 fC/pF. The current peaked 4.4 +/- 0.7 ms after the action potential upstroke and rapidly decayed to zero with a time constant of 7.4 +/- 0.6 ms. I(Kr) gradually increased during the plateau, peaked 7 ms before the time of maximum rate of repolarization (V(max)(-)) at -54.2 +/- 1.7 mV, had peak amplitude of 0.62 +/- 0.08 pA/pF, and integral of 57.6 +/- 6.7 fC/pF. I(K1) began to rise from -22.4 +/- 0.8 mV, peaked 1 ms after the time of V(max)(-) at -58.3 +/- 0.6 mV, had peak amplitude of 1.8 +/- 0.1 pA/pF, and integral of 61.6 +/- 6.2 fC/pF. Good correlation was observed between peak I(K1) and V(max)(-) (r = 0.93) but none between I(Kr) and V(max)(-). Neither I(K1) nor I(Kr) was frequency-dependent between 0.2 and 1.66 Hz. Congruently, I(Kr) failed to accumulate in canine myocytes at fast driving rates. CONCLUSION Terminal repolarization is dominated by I(K1), but action potential duration is influenced by several ion currents simultaneously. As I(to) was not active during the plateau, and neither I(K1) nor I(Kr) was frequency-dependent, other currents must be responsible for the frequency dependence of action potential duration at normal and slow heart rates in canine ventricular cells.
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Affiliation(s)
- T Bányász
- Department of Physiology, University of Debrecen, Debrecen, Hungary
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26
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Finer NN, Barrington KJ. Cochrane review: Nitric oxide for respiratory failure in infants born at or near term. ACTA ACUST UNITED AC 2007. [DOI: 10.1002/ebch.129] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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27
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Waelti ER, Barton M. Rapid Endocytosis of Copper-Zinc Superoxide Dismutase into Human Endothelial Cells: Role for Its Vascular Activity. Pharmacology 2006; 78:198-201. [PMID: 17077646 DOI: 10.1159/000096598] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2006] [Accepted: 09/12/2006] [Indexed: 11/19/2022]
Abstract
Cytosolic CuZn-SOD (SOD1) is a dimeric, carbohydrate-free enzyme with a molecular weight of about 32 kDa and also circulates in human blood plasma. Due to its molecular mass it has been believed that the enzyme cannot penetrate the cell membrane. Here we report that rapid endocytosis of FITC-CuZn-SOD into human endothelial cells occurs within 5 min. Moreover, relaxation of rat aortic rings in response to CuZn-SOD is associated with a lag time of 45-60 s and only observed in the presence of intact endothelial cells. The results indicate acute and rapid endothelial cell endocytosis of CuZn-SOD, possibly via activation of a receptor-mediated pathway. Intracellular uptake via endocytosis may contribute to the vascular effects of CuZn-SOD, including vasodilation, and is likely to play a role in regulation of vascular tone and diseases such as atherosclerosis.
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Affiliation(s)
- Ernst R Waelti
- Department of Medicine, Internal Medicine I, Medical Policlinic, University Hospital Zurich, Zurich, Switzerland
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Sahin AS, Atalik KE, Sahin TK, Doğan N. Cooling and response to hydrogen peroxide in human saphenous vein: role of the endothelium. Fundam Clin Pharmacol 2005; 19:341-6. [PMID: 15910658 DOI: 10.1111/j.1472-8206.2005.00330.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In the present work we studied the responses of human saphenous vein to H2O2 and effects of moderate cooling on these responses with analysis of the role of endothelium. H2O2 (10(-7)-10(-2) M) induced concentration-dependent contraction in the intact human saphenous vein strips at both temperatures. At 28 degrees C, the maximal contraction induced by H2O2 was significantly lower than that at 37 degrees C. Compared with intact strips, the sensitivity and the maximal contraction to H2O2 were significantly enhanced in endothelium-denuded strips at 37 and 28 degrees C. However, pD2 values and maximal contractions were not significantly different in endothelium-denuded strips at different temperatures. Pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME) increased significantly the maximal contraction and sensitivity to H2O2 at 37 and 28 degrees C. The contractions increased by L-NAME were restored by the pre-incubation of l-arginine (10(-3) M) at every temperature studied. The contractile responses of intact human saphenous veins to H2O2 were reduced significantly by 10(-5) M indomethacin at both temperatures. Our results suggest that H2O2-induced contraction of human saphenous vein are mediated by its direct effect on the smooth muscle and by the generation of products of the cyclooxygenase pathway from the endothelium. Signalling pathways of these contractile effects are the same at 37 and 28 degrees C. Under normal temperature conditions, the contraction to H2O2 is possibly modulated by endothelial nitric oxide. Cooling reduces the contraction to H2O2 by increasing release of nitric oxide.
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Affiliation(s)
- Ayşe Saide Sahin
- Department of Pharmacology, Meram Medicine Faculty, Selçuk University, Konya, Turkey.
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29
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Abstract
Opening of potassium channels on vascular smooth muscle cells with resultant hyperpolarization plays a central role in several mechanisms of vasodilation. For example, in the arteriolar circulation where tissue perfusion is regulated, there is an endothelial derived hyperpolarizing factor that opens vascular smooth muscle calcium-activated potassium channels, eliciting dilation. Metabolic vasodilation involves the opening of sarcolemmal ATP-sensitive potassium channels. Adrenergic dilation as well as basal vasomotor tone in several vascular beds depend upon voltage-dependent potassium channels in smooth muscle. Thus hyperpolarization through potassium channel opening is a fundamental mechanism for vasodilation. Disease states such as coronary atherosclerosis and its risk factors are associated with elevated levels of reactive oxygen (ROS) and nitrogen species that have well-defined inhibitory effects on nitric oxide-mediated vasodilation. Effects of ROS on hyperpolarization mechanisms of dilation involving opening of potassium channels are less well understood but are very important because hyperpolarization-mediated dilation often compensates for loss of other dilator mechanisms. We review the effect of ROS on potassium channel function in the vasculature. Depending on the oxidative species, ROS can activate, inhibit, or leave unaltered potassium channel function in blood vessels. Therefore, discerning the activity of enzymes regulating production or degradation of ROS is important when assessing tissue perfusion in health and disease.
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Affiliation(s)
- David D Gutterman
- Cardiovascular Center, Department of Medicine, General Clinical Research Center, VA Medical Center, Medical College of Wisconsin, Milwaukee 53226, USA.
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Ellis A, Triggle CR. Endothelium-derived reactive oxygen species: their relationship to endothelium-dependent hyperpolarization and vascular tone. Can J Physiol Pharmacol 2004; 81:1013-28. [PMID: 14719036 DOI: 10.1139/y03-106] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Opinions on the role of reactive oxygen species (ROS) in the vasculature have shifted in recent years, such that they are no longer merely regarded as indicators of cellular damage or byproducts of metabolism--they may also be putative mediators of physiological functions. Hydrogen peroxide (H2O2), in particular, can initiate vascular myocyte proliferation (and, incongruously, apoptosis), hyperplasia, cell adhesion, migration, and the regulation of smooth muscle tone. Endothelial cells express enzymes that produce ROS in response to various stimuli, and H2O2 is a potent relaxant of vascular smooth muscle. H2O2 itself can mediate endothelium-dependent relaxations in some vascular beds. Although nitric oxide (NO) is well recognized as an endothelium-derived dilator, it is also well established, particularly in the microvasculature, that another factor, endothelium-derived hyperpolarizing factor (EDHF), is a significant determinant of vasodilatory tone. This review primarily focuses on the hypothesis that H2O2 is an EDHF in resistance arteries. Putative endothelial sources of H2O2 and the effects of H2O2 on potassium channels, calcium homeostasis, and vascular smooth muscle tone are discussed. Furthermore, given the perception that ROS can more likely elicit cytotoxic effects than perform signalling functions, the arguments for and against H2O2 being an endogenous vasodilator are assessed.
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Affiliation(s)
- Anthie Ellis
- Smooth Muscle Research Group, Faculty of Medicine, University of Calgary, AB, Canada
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Fülöp L, Bányász T, Magyar J, Szentandrássy N, Varró A, Nánási PP. Reopening of L-type calcium channels in human ventricular myocytes during applied epicardial action potentials. ACTA ACUST UNITED AC 2004; 180:39-47. [PMID: 14706111 DOI: 10.1046/j.0001-6772.2003.01223.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
AIMS Present study was performed to compare the dynamics of human L-type calcium current (ICa,L) flowing during rectangular voltage pulses, voltage ramps, and action potentials (APs) recorded from epicardiac and endocardiac canine ventricular cells. METHODS ICa,L was recorded in single myocytes isolated from undiseased human hearts using the whole cell voltage clamp technique. RESULTS The decay of ICa,L was monotonic when using rectangular pulses or endocardial APs as voltage commands, whereas the current became double-peaked (displaying a second rise and fall) during epicardial (EPI) APs or voltage ramps used to mimic EPI APs. These ICa,L profiles were associated with single-hooked and double-hooked phase-plane trajectories, respectively. No sustained current was observed during the AP commands. Kinetics of deactivation and recovery from inactivation of human ICa,L were determined using twin-pulse voltage protocols and voltage ramps, and the results were similar to those obtained previously in canine cells under identical experimental conditions. CONCLUSIONS ICa,L can inactivate partially before and deactivate during the phase-1 repolarization of the epicardiac AP, and reopening of these channels seems to be associated with formation of the dome.
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Affiliation(s)
- L Fülöp
- Department of Physiology, University Medical School of Debrecen, Debrecen, Hungary
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Burman KJ, Sartor DM, Verberne AJM, Llewellyn-Smith IJ. Cocaine- and amphetamine-regulated transcript in catecholamine and noncatecholamine presympathetic vasomotor neurons of rat rostral ventrolateral medulla. J Comp Neurol 2004; 476:19-31. [PMID: 15236464 DOI: 10.1002/cne.20198] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Presympathetic vasomotor adrenergic (C1) and nonadrenergic (non-C1) neurons in the rostral ventrolateral medulla (RVLM) provide the main excitatory drive to cardiovascular sympathetic preganglionic neurons in the spinal cord. C1 and non-C1 neurons contain cocaine- and amphetamine-regulated transcript (CART), suggesting that CART may be a common marker for RVLM presympathetic neurons. To test this hypothesis, we first used double-immunofluorescence staining for CART and tyrosine hydroxylase (TH) to quantify CART-immunoreactive (-IR) catecholamine and noncatecholamine neurons in the C1 region. Next, we quantified the proportion of CART-IR RVLM neurons that expressed Fos in response to a hypotensive stimulus, using peroxidase immunohistochemistry for Fos and dual immunofluorescence for CART and TH. Finally, we fluorescently detected CART immunoreactivity in electrophysiologically identified, juxtacellularly labeled RVLM presympathetic neurons. In the RVLM, 97% of TH-IR neurons were CART-IR, and 74% of CART-IR neurons were TH-IR. Nitroprusside infusion significantly increased the number of Fos-IR RVLM neurons compared with saline controls. In nitroprusside-treated rats, virtually all Fos/TH neurons in the RVLM were immunoreactive for CART (98% +/- 1.3%, SD; n = 7), whereas 29% +/- 8.3% of CART-positive, TH-negative neurons showed Fos immunoreactivity. Six fast (2.8-5.8 m/second, noncatecholamine)-, two intermediate (2.1 and 2.2 m/second)-, and five slow (<1 m/second, catecholamine)-conducting RVLM presympathetic vasomotor neurons were juxtacellularly labeled. After fluorescent detection of CART and biotinamide, all 13 neurons were found to be CART-IR. These results suggest that, in rat RVLM, all catecholamine and noncatecholamine presympathetic vasomotor neurons contain CART.
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Affiliation(s)
- Kathleen J Burman
- Cardiovascular Medicine and Centre for Neuroscience, Flinders University, Bedford Park, South Australia 5042, Australia
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Sun W, Panneton WM. Defining projections from the caudal pressor area of the caudal ventrolateral medulla. J Comp Neurol 2004; 482:273-93. [PMID: 15690490 DOI: 10.1002/cne.20434] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We previously defined a functional area in the caudal medulla oblongata that elicits an increase in arterial pressure when stimulated (Sun and Panneton [2002] Am. J. Physiol. 283:R768-R778). In the present study, anterograde and retrograde tracing techniques were used to investigate the projections of this caudal pressor area (CPA) to the medulla and pons. Injections of biotinylated dextran amine into the CPA resulted in numerous labeled fibers with varicosities in the ipsilateral subnucleus reticularis dorsalis, commissural subnucleus of the nucleus tractus solitarii, lateral medulla, medial facial nucleus, A5 area, lateral vestibular nucleus, and internal lateral subnucleus of the parabrachial complex. Sparser projections were found ipsilaterally in the pressor and depressor areas of the medulla and the spinal trigeminal nucleus and contralaterally in the CPA. Injections of the retrograde tracer Fluoro-Gold into these areas labeled neurons in the CPA as well as the nearby medullary dorsal horn and reticular formation. However, we conclude that the CPA projects preferentially to the subnucleus reticularis dorsalis, commissural nucleus tractus solitarii, lateral medulla, A5 area, and internal lateral parabrachial nucleus. Weaker projections were seen to the CVLM and RVLM and to the contralateral CPA. The projection to the facial nucleus arises from nearby reticular neurons, whereas projections to the vestibular nucleus arise from the lateral reticular nucleus. Labeled neurons in the CPA consisted mostly of small bipolar and some triangular neurons. The projection to the CVLM, or to A5 area, may provide for the increase in arterial pressure with CPA stimulation. However, most of the projections described herein are to nuclei implicated in the processing of noxious information. This implies a unique role for the CPA in somatoautonomic regulation.
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Affiliation(s)
- Wei Sun
- Department of Anatomy and Neurobiology, St. Louis University School of Medicine, St. Louis, Missouri 63104-1004, USA
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Shiels HA, Vornanen M, Farrell AP. Temperature dependence of cardiac sarcoplasmic reticulum function in rainbow trout myocytes. J Exp Biol 2002; 205:3631-9. [PMID: 12409489 DOI: 10.1242/jeb.205.23.3631] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYTo explore how the cardiac sarcoplasmic reticulum (SR) functions over a range of temperatures, we used whole-cell voltage clamp combined with rapid caffeine application to study SR Ca2+ accumulation, release and steady-state content in atrial myocytes from rainbow trout. Myocytes were isolated from rainbow trout acclimated to 14°C, and the effect of varying stimulation pulse number, frequency and experimental temperature (7°C,14°C and 21°C) on SR function was studied. To add physiological relevance, in addition to 200 ms square (SQ) voltage pulses, myocytes were stimulated with temperature-specific action potentials (AP) applied at relevant frequencies for each test temperature. We found that the SR accumulated Ca2+ more rapidly and to a greater concentration(1043±189 μmol l-1 Ca2+, 1138±173μmol l-1 Ca2+, and 1095±142 μmol l-1 Ca2+ at 7°C, 14°C and 21°C,respectively) when stimulated with physiological AP waveforms at physiological frequencies compared with 200 ms SQ pulses at the same frequencies(664±180 μmol l-1 Ca2+, 474±75 μmol l-1 Ca2+ and 367±42 μmol l-1Ca2+ at 7°C, 14°C and 21°C, respectively). Also, and in contrast to 200 ms SQ pulse stimulation, temperature had little effect on steady-state SR Ca2+ accumulation during AP stimulation. Furthermore, we observed SR-Ca2+-dependent inactivation of the L-type Ca2+ channel current (ICa) at 7°C, 14°C and 21°C, providing additional evidence of maintained SR function in fish hearts over an acute range of temperatures. We conclude that the waveform of the AP may be critical in ensuring adequate SR Ca2+ cycling during temperature change in rainbow trout in vivo.
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Affiliation(s)
- Holly A Shiels
- Simon Fraser University, Biological Sciences, Burnaby, British Columbia, V5A 1S6, Canada.
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Bers DM. Regulation of Cellular Calcium in Cardiac Myocytes. Compr Physiol 2002. [DOI: 10.1002/cphy.cp020109] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Dobrzynski H, Janvier NC, Leach R, Findlay JBC, Boyett MR. Effects of ACh and adenosine mediated by Kir3.1 and Kir3.4 on ferret ventricular cells. Am J Physiol Heart Circ Physiol 2002; 283:H615-30. [PMID: 12124209 DOI: 10.1152/ajpheart.00130.2002] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The inotropic effects of ACh and adenosine on ferret ventricular cells were investigated with the action potential-clamp technique. Under current clamp, both agonists resulted in action potential shortening and a decrease in contraction. Under action potential clamp, both agonists failed to decrease contraction substantially. In the absence of agonist, application of the short action potential waveform (recorded previously in the presence of agonist) also resulted in a decrease in contraction. Under action potential clamp, application of ACh resulted in a Ba(2+)-sensitive outward current with the characteristics of muscarinic K+ current (I(K,ACh)); the presence of the muscarinic K+ channel was confirmed by PCR and immunocytochemistry. In the absence of agonist, on application of the short ACh action potential waveform, the decrease in contraction was accompanied by loss of the inward Na(+)/Ca(2+) exchange current (I(NaCa)). ACh also inhibited the background inward K+ current (I(K,1)). It is concluded that ACh activates I(K,ACh), inhibits I(K,1), and indirectly inhibits I(NaCa); this results in action potential shortening, decrease in contraction, and, as a result of the inhibition of I(K,1), minimum decrease in excitability.
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Affiliation(s)
- H Dobrzynski
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom
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Yamamoto H, Lee CE, Marcus JN, Williams TD, Overton JM, Lopez ME, Hollenberg AN, Baggio L, Saper CB, Drucker DJ, Elmquist JK. Glucagon-like peptide-1 receptor stimulation increases blood pressure and heart rate and activates autonomic regulatory neurons. J Clin Invest 2002. [DOI: 10.1172/jci0215595] [Citation(s) in RCA: 370] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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Janczewski AM, Spurgeon HA, Lakatta EG. Action potential prolongation in cardiac myocytes of old rats is an adaptation to sustain youthful intracellular Ca2+ regulation. J Mol Cell Cardiol 2002; 34:641-8. [PMID: 12054851 DOI: 10.1006/jmcc.2002.2004] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Advanced age in rats is accompanied by reduced expression of the sarcoplasmic reticulum (SR) Ca2+ pump (SERCA-2). The amplitudes of intracellular Ca2+ (Ca2+(i)) transients and contractions in ventricular myocytes isolated from old (23-24-months) rats (OR), however, are similar to those of young (4-6-months) rat myocytes (YR). OR myocytes also manifest slowed inactivation of L-type Ca2+ current (I(CaL)) and marked prolongation of action potential (AP) duration. To determine whether and how age-associated AP prolongation preserves the Ca2+(i) transient amplitude in OR myocytes, we employed an AP-clamp technique with simultaneous measurements of I(CaL) (with Na+ current, K+ currents and Ca2+ influx via sarcolemmal Na+-Ca2+ exchanger blocked) and Ca2+(i) transients in OR rat ventricular myocytes dialyzed with the fluorescent Ca2+ probe, indo-1. Myocytes were stimulated with AP-shaped voltage clamp waveforms approximating the configuration of prolonged, i.e. the native, AP of OR cells (AP-L), or with short AP waveforms (AP-S), typical of YR myocytes. Changes in SR Ca2+ load were assessed by rapid, complete SR Ca2+ depletions with caffeine. As expected, during stimulation with AP-S vs AP-L, peak I(CaL) increased, by 21+/-4%, while the I(CaL) integral decreased, by 19+/-3% (P<0.01 for each). Compared to AP-L, stimulation of OR myocytes with AP-S reduced the amplitudes of the Ca2+(i) transient by 31+/-6%, its maximal rate of rise (+dCa2+(i)/dt(max); a sensitive index of SR Ca2+ release flux) by 37+/-4%, and decreased the SR Ca2+ load by 29+/-4% (P<0.01 for each). Intriguingly, AP-S also reduced the maximal rate of the Ca2+(i) transient relaxation and prolonged its time to 50% decline, by 35+/-5% and 33+/-7%, respectively (P<0.01 for each). During stimulation with AP-S, the gain of Ca2+-induced Ca2+ release (CICR), indexed by +dCa2+(i)/dt(max)/I(CaL), was reduced by 46+/-4% vs AP-L (P<0.01). We conclude that the effects of an application of a shorter AP to OR myocytes to reduce +dCa2+(i)/dt(max) and the Ca2+ transient amplitude are attributable to a reduction in SR Ca2+ load, presumably due to a reduced I(CaL) integral and likely also to an increased Ca2+ extrusion via sarcolemmal Na+-Ca2+ exchanger. The decrease in the Ca2+(i) transient relaxation rate in OR cells stimulated with shorter APs may reflect a reduction of Ca2+/calmodulin-kinase II-regulated modulation of Ca2+ uptake via SERCA-2, consequent to a reduced local Ca2+ release in the vicinity of SERCA-2, also attributable to reduced SR Ca2+ load. Thus, the reduction of CICR gain during stimulation with AP-S is the net result of both a diminished SR Ca2+ release and an increased peak I(CaL). These results suggest that ventricular myocytes of old rats utilize AP prolongation to preserve an optimal SR Ca2+ loading, CICR gain and relaxation of Ca2+(i) transients.
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Affiliation(s)
- Andrzej M Janczewski
- Laboratory of Cardiovascular Science, Gerontology Research Center, Intramural Research Program, National Institute on Aging, National Institutes of Health, 5600 Nathan Shock Drive, Baltimore, MD 21224-6823, USA
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Lambert GW. Paring down on Descartes: a review of brain noradrenaline and sympathetic nervous function. Clin Exp Pharmacol Physiol 2001; 28:979-82. [PMID: 11903297 DOI: 10.1046/j.1440-1681.2001.03578.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
1. The conceptual framework of mind-body interaction can be traced back to the seminal observations of the French philosopher and mathematician René Descartes (1596-1650). Descartes succeeded in eliminating the soul's apparent physiological role and established the brain as the body's control centre. 2. While the pivotal role played by the central nervous system (CNS) in the maintenance of physiological and psychological health has long been recognized, the development of methods designed for the direct examination of human CNS processes has only recently come to fruition. 3. There exists a substantial body of evidence derived from clinical and experimental studies indicating that CNS monoaminergic cell groups, in particular those using noradrenaline as their neurotransmitter, participate in the excitatory regulation of the sympathetic nervous system and the development and maintenance of the hypertensive state. 4. In essential hypertension, particularly in younger patients, there occurs an activation of sympathetic nervous outflows to the kidneys, heart and skeletal muscle. The existence of a correlation between subcortical brain noradrenaline turnover and total body noradrenaline spillover to plasma, resting blood pressure and heart rate provides further support for the observation that elevated subcortical noradrenergic activity subserves a sympathoexcitatory role in the regulation of sympathetic preganglionic neurons of the thorocolumbar cord.
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Affiliation(s)
- G W Lambert
- Human Neurotransmitter Laboratory, Baker Medical Research Institute, Melbourne, Victoria, Australia.
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Abstract
Although the pivotal role played by the brain in the maintenance of optimal physiologic and psychologic health has long been recognized, methods for the direct examination of human central nervous system processes have only recently been developed. A growing body of evidence indicates that central nervous systemmonoaminergic cell groups, in particular those utilizing norepinephrine as their neurotransmitter, participate in the excitatory regulation of the sympathetic nervous system and the development of the hypertensive state.
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Affiliation(s)
- G W Lambert
- Human Neurotransmitters Laboratory, Baker Medical Research Institute, PO Box 6492, St. Kilda Road Central, Melbourne, Victoria 8008, Australia.
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Convery MK, Hancox JC. Na+-Ca2+ exchange current from rabbit isolated atrioventricular nodal and ventricular myocytes compared using action potential and ramp waveforms. ACTA PHYSIOLOGICA SCANDINAVICA 2000; 168:393-401. [PMID: 10712577 DOI: 10.1046/j.1365-201x.2000.00681.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We measured and compared Na-Ca exchanger current (INa-Ca) from rabbit isolated ventricular and atrioventricular (AV) nodal myocytes, using action potential (AP) and ramp voltage commands. Whole cell patch-clamp recordings were made at 35-37 degrees C; INa-Ca was measured as 5 mM nickel (Ni)- sensitive current with major interfering voltage and calcium-activated currents blocked. In ventricular cells a 2-s descending ramp elicited INa-Ca showing outward rectification and a reversal potential (Erev) of -13.1 +/- 1. 2 mV (n = 12; mean +/- SEM). With a ventricular AP as the voltage command, the profile of INa-Ca followed the applied waveform closely. The current-voltage relation during AP repolarization was almost linear and showed an Erev of -38.3 +/- 5.3 mV (n = 6). As INa-Ca depended on the applied voltage waveform, comparisons between the two cell types utilized the same command waveform (a series of AV nodal APs). In ventricular myocytes this elicited INa-Ca that reversed near -38 mV and was inwardly directed during the pacemaker potential. This command was also applied to AV node cells; mean INa-Ca density at all voltages encompassed by the AP (-70 to +30 mV) did not differ significantly from that in ventricular myocytes (P > 0.05, ANOVA). This finding was confirmed using brief (250 ms) voltage ramp protocols (P > 0.1 ANOVA). These data represent the first direct measurements of AV nodal INa-Ca and suggest that the exchanger may be functionally expressed to similar levels in the two cell types. They may also suggest a possible role for INa-Ca during the pacemaker potential in AV node as inward INa-Ca was observed over the pacemaker potential range even with bulk internal Ca buffered to a low level.
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Affiliation(s)
- M K Convery
- Department of Physiology & Cardiovascular Research Laboratories, School of Medical Sciences, University Walk, Bristol, UK
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Puglisi JL, Yuan W, Bassani JW, Bers DM. Ca(2+) influx through Ca(2+) channels in rabbit ventricular myocytes during action potential clamp: influence of temperature. Circ Res 1999; 85:e7-e16. [PMID: 10488061 DOI: 10.1161/01.res.85.6.e7] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Ca(2+) influx via Ca(2+) current (I(Ca)) during the action potential (AP) was determined at 25 degrees C and 35 degrees C in isolated rabbit ventricular myocytes using AP clamp. Contaminating currents through Na(+) and K(+) channels were eliminated by using Na(+)- and K(+)-free solutions, respectively. DIDS (0.2 mmol/L) was used to block Ca(2+)-activated chloride current (I(Cl(Ca))). When the sarcoplasmic reticulum (SR) was depleted of Ca(2+) by preexposure to 10 mmol/L caffeine, total Ca(2+) entry via I(Ca) during the AP was approximately 12 micromol/L cytosol (at both 25 degrees C and 35 degrees C). Similar Ca(2+) influx at 35 degrees C and 25 degrees C resulted from a combination of higher and faster peak I(Ca), offset by more rapid I(Ca) inactivation at 35 degrees C. During repeated AP clamps, the SR gradually fills with Ca(2+), and consequent SR Ca(2+) release accelerates I(Ca) inactivation during the AP. During APs and contractions in steady state, total Ca(2+) influx via I(Ca) was reduced by approximately 50% but was again unaltered by temperature (5.6+/-0.2 micromol/L cytosol at 25 degrees C, 6.0+/-0.2 micromol/L cytosol at 35 degrees C). Thus, SR Ca(2+) release is responsible for sufficient I(Ca) inactivation to cut total Ca(2+) influx in half. However, because of the kinetic differences in I(Ca), the amount of Ca(2+) influx during the first 10 ms, which presumably triggers SR Ca(2+) release, is much greater at 35 degrees C. I(Ca) during a first pulse, given just after the SR was emptied with caffeine, was subtracted from I(Ca) during each of 9 subsequent pulses, which loaded the SR. These difference currents reflect I(Ca) inactivation due to SR Ca(2+) release and thus indicate the time course of local [Ca(2+)] in the subsarcolemmal space near Ca(2+) channels produced by SR Ca(2+) release (eg, maximal at 20 ms after the AP activation at 35 degrees C). Furthermore, the rate of change of this difference current may reflect the rate of SR Ca(2+) release as sensed by L-type Ca(2+) channels. These results suggest that peak SR Ca(2+) release occurs within 2.5 or 5 ms of AP upstroke at 35 degrees C and 25 degrees C, respectively. I(Cl(Ca)) might also indicate local [Ca(2+)], and at 35 degrees C in the absence of DIDS (when I(Cl(Ca)) is prominent), peak I(Cl(Ca)) also occurred at a time comparable to the peak I(Ca) difference current. We conclude that SR Ca(2+) release decreases the Ca(2+) influx during the AP by approximately 50% (at both 25 degrees C and 35 degrees C) and that changes in I(Ca) (and I(Cl(Ca))), which depend on SR Ca(2+) release, provide information about local subsarcolemmal [Ca(2+)].
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Affiliation(s)
- J L Puglisi
- Department of Physiology, Loyola University Chicago, Maywood, IL 60153, USA
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Jansson T, Lambert GW. Effect of intrauterine growth restriction on blood pressure, glucose tolerance and sympathetic nervous system activity in the rat at 3-4 months of age. J Hypertens 1999; 17:1239-48. [PMID: 10489100 DOI: 10.1097/00004872-199917090-00002] [Citation(s) in RCA: 121] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVE Epidemiological studies suggest that intrauterine growth restriction (IUGR) due to maternal undernutrition during pregnancy represents a major risk factor for hypertension and diabetes in adult age. However, placental insufficiency, rather than maternal malnutrition, is the main cause of IUGR in the Western world. We therefore studied the relationship between birth weight and adult blood pressure and glucose tolerance in an established animal model of placental insufficiency. DESIGN IUGR was induced by uterine artery ligation in pregnant rats and the offspring were studied at 3-4 months of age. METHODS In one subgroup of animals (n = 41, birth weight range 3.2-6.6 g) blood pressure was recorded over 72 h using telemetry and hypothalamic tissue levels of noradrenaline was measured. In another subgroup (n = 30, birth weight range 3.0-6.8 g) the activity of the sympathetic nervous system (SNS) was assessed by noradrenaline isotope dilution techniques and glucose tolerance determined by an intravenous glucose load. RESULTS Adult blood pressure was independent of birth weight Haemodynamic responses of IUGR rats to moderate sound stress was unaltered. In male rats neither SNS activity, hypothalamic noradrenaline concentrations nor glucose tolerance was associated with birth weight In contrast, IUGR in female rats was associated with increased SNS activity, elevated fasting blood glucose as well as lower insulin and higher glucose levels in response to a glucose load. CONCLUSION IUGR is not linked to an elevated blood pressure at 3-4 months of age in this model. However, in female rats, IUGR is associated with increased SNS activity and impaired glucose tolerance in adult life.
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Affiliation(s)
- T Jansson
- Perinatal Center, Department of Physiology and Pharmacology, Göteborg University, Sweden.
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Linz KW, Meyer R. Control of L-type calcium current during the action potential of guinea-pig ventricular myocytes. J Physiol 1998; 513 ( Pt 2):425-42. [PMID: 9806993 PMCID: PMC2231304 DOI: 10.1111/j.1469-7793.1998.425bb.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. During an action potential the L-type Ca2+ current (ICa,L) activates rapidly, then partially declines leading to a sustained inward current during the plateau phase. The reason for the sustained part of ICa,L has been investigated here. 2. In the present study the mechanisms controlling the ICa,L during an action potential were investigated quantitatively in isolated guinea-pig ventricular myocytes by whole-cell patch clamp. To measure the actual time courses of ICa,L and the corresponding L-type channel inactivation (fAP) during an action potential, action potential-clamp protocols combined with square pulses were applied. 3. Within the first 10 ms of the action potential the ICa,L rapidly inactivated by about 50 %; during the plateau phase inactivation proceeded to 95 %. Later, during repolarization, the L-type channels recovered up to 25 %. 4. The voltage-dependent component of inactivation during an action potential was determined from measurements of L-type current carried by monovalent cations. This component of inactivation proceeded rather slowly and contributed only a little to fAP. ICa,L during an action potential is thus mainly controlled by Ca2+-dependent inactivation. 5. In order to investigate the source of the Ca2+ controlling fAP, internal Ca2+ homeostasis was manipulated by the use of Ca2+ buffers (EGTA, BAPTA), by blocking Na+-Ca2+ exchange, or by blocking Ca2+ release from the sarcoplasmic reticulum (SR). Internal BAPTA markedly reduced the L-type channel inactivation during the entire action potential, whereas EGTA affected fAP only during the middle and late plateau phases. Inhibition of Na+-Ca2+ exchange markedly increased inactivation of L-type channels. Although blocking SR Ca2+ release decreased the fura-2-measured cytoplasmic Ca2+ concentration ([Ca2+]i) transient by about 90 %, it reduced L-type channel inactivation only during the initial 50 ms of the action potential. Thus, it is Ca2+ entering the cell through the L-type channels that controls the inactivation process for the majority of the action potential. Nevertheless, SR Ca2+-release contributes 40-50 % to L-type channel inactivation during the initial period of the action potential. However, the maximum extent of inactivation reached during the plateau is independent of Ca2+ released from the SR. 6. For the first time, the actual time course of L-type channel inactivation has been directly determined during an action potential under various defined [Ca2+]i conditions. Thereby, the relative contribution to ICa,L inactivation of voltage, Ca2+ entering through L-type channels, and Ca2+ being released from the SR could be directly demonstrated.
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Affiliation(s)
- K W Linz
- Physiological Institute, University of Bonn, Wilhelmstrasse 31, D-53111 Bonn, Germany
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Hove-Madsen L, Tort L. L-type Ca2+ current and excitation-contraction coupling in single atrial myocytes from rainbow trout. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:R2061-9. [PMID: 9843898 DOI: 10.1152/ajpregu.1998.275.6.r2061] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have examined the contribution of L-type Ca2+ current (ICa) to the activation of contraction in trout atrial myocytes under basal and phosphorylating conditions. The average myocyte length was 197 +/- 14 micrometer, width was 5.5 +/- 0.2 micrometer, and cell capacitance was 36.2 +/- 2.2 pF. With 25 microM EGTA in the patch pipette and a stimulation frequency of 0.125 Hz, ICa was 2.6 +/- 0.4 pA/pF and it carried a total charge of 0.10 +/- 0.01 pC/pF, giving rise to a contraction of 15.2 +/- 2.8% of the resting cell length. With a cell volume of 2.4 +/- 0.3 pl, the charge carried by ICa corresponded to 14.7 +/- 2.2 micromol Ca2+/l nonmitochondrial cell volume (microM). This can account for only 30-40% of the Ca2+ binding to the myofilaments during a contraction. Increasing the stimulation frequency from 0.25 to 2 Hz decreased ICa amplitude and charge by 66 +/- 5 and 80 +/- 3%, respectively. Elevating the pipette EGTA concentration from 25 microM to 5 mM increased ICa amplitude and charge by approximately 290%. Both isoproterenol and cAMP increased ICa by approximately 230%. The total charge carried by the isoproterenol- or cAMP-stimulated current was increased by 170%. We conclude that the use of high-EGTA concentration may overestimate the total Ca2+ carried by ICa under physiological conditions. Furthermore, the results suggest that, in contrast to previous reports from other lower vertebrates, Ca2+ flux through L-type Ca2+ channels alone is not sufficient to fully activate contraction in trout atrial myocytes at room temperature.
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Affiliation(s)
- L Hove-Madsen
- Department of Physiology and Cell Biology, Faculty of Science, Universitat Autonoma de Barcelona, 08193 Cerdanyola, Barcelona, Spain
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Wahn H, Hammerschmidt S. Inhibition of PMN- and HOC1-induced vascular injury in isolated rabbit lungs by acetylsalicylic acid: a possible link between neutrophil-derived oxidative stress and eicosanoid metabolism? BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1408:55-66. [PMID: 9784604 DOI: 10.1016/s0925-4439(98)00055-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Neutrophils are involved in the pathogenesis of acute lung injury. The neutrophil-derived enzyme myeloperoxidase (MPO) catalyzes the formation of the oxidant hypochlorous acid (HOCl). This study characterizes the effects of (A) continuous HOCl infusion, and (B) stimulated neutrophils on pulmonary circulation in an isolated rabbit lung model. Furthermore, the effect of cyclooxygenase inhibition by acetylsalicylic acid (ASA, 0.5 mM) on these effects was investigated. (A) Infusion of HOCl (in nmol min-1, groups: 0, 0+ASA, 1000, 1000+ASA, 2000, and 2000+ASA) into the isolated organ was started after a 45-min steady-state period (t=0). (B) Neutrophils (PMN group: 1480+/-323 and ASA group 1294+/-320 microliter-1) were added into the perfusate between (t=-45 min) and stimulated with FMLP (1 microM) after two 45-min steady-state periods (t=0). Perfusate MPO activity was measured at t=-90, -45, 0, 1, 2, 3, 5, 10, 15, 30, 60, and 90 min. For both groups, pulmonary artery pressure (PAP) and lung weight were continuously recorded and the capillary filtration coefficient (Kf,c in 10(-4) cm(3) s(-1) cm H2O(-1) g(-1) was calculated from the slope of weight gain after a hydrostatic challenge at t=-45, -15, 30, 60 and 90 min. (A) Continuous HOCl infusion (1000/2000 nmol min-1) evoked a significant increase in DeltaPAP and an up to 10-fold increase in Kf,c reaching the maximum extent of the observed effects significant earlier in the 2000 nmol min-1 group. ASA reduced DeltaPAPmax significantly to about 50% in corresponding groups and the increase in PAP and Kf,c occurred later in the ASA groups. (B) Neutrophil stimulation (PMN group/ASA group) evoked a rapid increase in DeltaPAP and MPO activity, while the changes in vascular permeability were rather moderate, but still significant. The release of MPO activity was similar in both groups. ASA significantly reduced the increase in DeltaPAP without affecting the release of MPO activity. Compared to baseline values, the preventive effects on vascular permeability increase reached level of significance as well. In summary, the described changes in pulmonary circulation caused by HOCl infusion or by neutrophil stimulation are significantly reduced by ASA. An involvement of cyclooxygenase products in the mediation of neutrophil-derived oxidative stress could be concluded.
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Affiliation(s)
- H Wahn
- Department of Cardiology and Pulmonology, University Göttingen, Göttingen, Germany.
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Affiliation(s)
- J G Borst
- Abteilung Zellphysiologie, Max-Planck Institut für Medizinische Forschung, Heidelberg, Germany
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Muller CA, Opie LH, McCarthy J, Hofmann D, Pineda CA, Peisach M. Effects of mibefradil, a novel calcium channel blocking agent with T-type activity, in acute experimental myocardial ischemia: maintenance of ventricular fibrillation threshold without inotropic compromise. J Am Coll Cardiol 1998; 32:268-74. [PMID: 9669280 DOI: 10.1016/s0735-1097(98)00182-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
OBJECTIVES We tested whether mibefradil, a selective T-type calcium channel blocking agent, could differentially inhibit experimental ventricular arrhythmogenesis more than contractility during acute regional ischemia and reperfusion compared with that during L-channel blockade by verapamil. BACKGROUND T-type calcium channels are found in nodal and conduction tissue and in vascular smooth muscle, but in much lower density in contractile myocardium. The potential role of mibefradil in ventricular arrhythmogenesis remains unclear. METHODS Mibefradil (Ro 40-5967, 1 mg/kg body weight intravenously [i.v.]) was given as a bolus 30 min before anterior descending coronary artery ligation, followed by 2 mg/kg per h i.v. during 20 min of ischemia and 25 min of reperfusion in open chest pigs. In a second group, mibefradil was given in a dose twice as high. A third group received verapamil (0.3 mg/kg i.v.), followed by an infusion of 0.6 mg/kg per h. RESULTS During the ischemic period, the low (clinically relevant) dose of mibefradil prevented the fall of the ventricular fibrillation threshold, without depressing the maximal rate of pressure development of the left ventricle (LVmax dP/dt). This low dose increased left ventricular blood flow, whereas peripheral arterial pressure remained unchanged. The higher dose of both mibefradil and verapamil was antiarrhythmic during ischemia, at the cost of depressed contractile activity. During reperfusion, only the higher dose of mibefradil and verapamil was antiarrhythmic but both depressed contractile activity. CONCLUSIONS Mibefradil is antiarrhythmic, without inotropic compromise. Speculatively, both T-type and L-type calcium channel blockade are involved in these effects.
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Affiliation(s)
- C A Muller
- Medical Research Council Heart Research Group, Cape Heart Centre, University of Cape Town, South Africa.
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Greene JG, Sheu SS, Gross RA, Greenamyre JT. 3-Nitropropionic acid exacerbates N-methyl-D-aspartate toxicity in striatal culture by multiple mechanisms. Neuroscience 1998; 84:503-10. [PMID: 9539220 DOI: 10.1016/s0306-4522(97)00389-8] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We examined the effects of 3-nitropropionic acid-induced succinate dehydrogenase inhibition on neuronal ATP content, N-methyl-D-aspartate-induced neuronal death, resting membrane potential, and N-methyl-D-aspartate-induced changes in cytosolic calcium concentration ([Ca2+]c) in cultured rat striatal neurons. Exposure of cultures to 3 mM 3-nitropropionic acid for 3 h did not cause overt toxicity, but reduced ATP content by 35%. Treatment with 3-nitropropionic, or removal of Mg2+ from the medium, enhanced subsequent N-methyl-D-aspartate toxicity, reducing the LC50 from 250 microM to 12 microM or 30 microM, respectively. Even after Mg2+ removal, enhancement of N-methyl-D-aspartate toxicity by 3-nitropropionic acid remained pronounced, with the LC50 further decreasing to 3 microM. The mean resting membrane potential of neurons treated with 3-nitropropionic acid was -37 mV, while that in control neurons was -61 mV. Treatment with 3-nitropropionic did not affect baseline [Ca2+]c as determined by fura-2 microfluorimetry. N-methyl-D-aspartate (30 microM) caused a rapid rise in [Ca2+]c, the initial magnitude of which was not affected by 3-nitropropionic acid. However, after a 1-h treatment, [Ca2+]c was dramatically higher in 3-nitropropionic acid-treated neurons. This increased calcium load was washed out slowly and only partially, although calcium in control neurons washed out rapidly and almost completely. These results suggest that in striatal neurons, the enhancement of N-methyl-D-aspartate toxicity caused by succinate dehydrogenase inhibition may be due to synergism between partial relief of the Mg2+ blockade of the N-methyl-D-aspartate receptor and other mechanisms, including disruption of neuronal calcium regulation. This synergism may be relevant to the neuronal death observed in neurodegenerative disorders.
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Affiliation(s)
- J G Greene
- Department of Neurobiology and Anatomy, University of Rochester Medical Center, NY 14642, USA
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Abstract
Calcium ions are key intracellular messengers in the cardiovascular system. Calcium homeostasis is regulated by an extracellular cycle, which controls the entry and removal of calcium between the cytosol and extracellular space, and an intracellular cycle, which controls calcium fluxes between the cytosol and intracellular stores in the sarcoplasmic reticulum. Several protein families mediate these calcium fluxes including those that (1) regulate the entry of calcium into the cytosol; (2) recognize calcium within the cytosol; and (3) remove calcium from the cytosol. Intracellular calcium binding proteins (the "E-F hand" proteins) recognize the appearance of calcium in the cytosol; in the heart and vascular smooth muscle, these proteins initiate excitation-contraction coupling. Calcium efflux occurs via adenosine triphosphate (ATP)-dependent calcium pumps and sodium-calcium exchangers, while two families of channels--intracellular release calcium channels and plasma membrane calcium channels--regulate calcium entry into the cytosol. The plasma membrane calcium channels, which include the L- and T-type channels, are of the greatest clinical interest because they are targets for pharmacologic therapy. T-type calcium channels, which activate contraction in vascular smooth muscle but have little or no role in cardiac excitation-contraction coupling, appear to be involved in signal transduction pathways that promote cell growth and proliferation. Calcium channel blockers that selectively block T-type calcium channels, therefore, offer a novel approach to cardiovascular drug therapy.
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Affiliation(s)
- A M Katz
- Cardiology Division, University of Connecticut Health Center, Farmington 06030-1305, USA
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