Essential role of diastolic oscillatory potentials in adrenergic control of guinea pig sino-atrial node discharge
<p>Abstract</p> <p>Background</p> <p>The diastolic oscillatory after-potential V<sub>os </sub>and pre-potential ThV<sub>os </sub>play an essential role in the pacemaker mechanism of sino-atrial node (SAN). The aim of this study was to investigate...
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| Format: | Article |
| Language: | English |
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BMC
2009-01-01
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| Series: | Journal of Biomedical Science |
| Online Access: | http://www.jbiomedsci.com/content/16/1/101 |
| _version_ | 1811277575205421056 |
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| author | Vassalle Mario Catanzaro John Nett Michael Rota Marcello |
| author_facet | Vassalle Mario Catanzaro John Nett Michael Rota Marcello |
| author_sort | Vassalle Mario |
| collection | DOAJ |
| description | <p>Abstract</p> <p>Background</p> <p>The diastolic oscillatory after-potential V<sub>os </sub>and pre-potential ThV<sub>os </sub>play an essential role in the pacemaker mechanism of sino-atrial node (SAN). The aim of this study was to investigate whether these oscillatory potentials are also involved in adrenergic control of SAN discharge.</p> <p>Methods</p> <p>V<sub>os </sub>and ThV<sub>os </sub>were visualized by superfusing guinea pig SAN in high [K<sup>+</sup>]<sub>o</sub>. The actions of adrenergic agonists on oscillatory potentials were studied by means of a microelectrode technique. Statistical significance was determined by means of Student's paired <it>t</it>-test.</p> <p>Results</p> <p>In non-spontaneous SAN, norepinephrine (NE) decreased the resting potential into a voltage range ("oscillatory zone") where increasingly larger ThV<sub>os </sub>appeared and initiated spontaneous discharge. In slowly discharging SAN, NE gradually increased the rate by increasing the amplitude and slope of earlier-occurring ThV<sub>os </sub>and of V<sub>os </sub>until these oscillations fused with initial diastolic depolarization (DD<sub>1</sub>). In the presence of NE, sudden fast rhythms were initiated by large V<sub>os </sub>that entered a more negative oscillatory zone and initiated a large ThV<sub>os</sub>. Recovery from NE exposure involved the converse changes. The β-adrenergic agonist isoproterenol had similar actions. Increasing calcium load by decreasing high [K<sup>+</sup>]<sub>o</sub>, by fast drive or by recovery in Tyrode solution led to growth of V<sub>os </sub>and ThV<sub>os </sub>which abruptly fused when a fast sudden rhythm was induced. Low [Ca<sup>2+</sup>]<sub>o </sub>antagonized the adrenergic actions. Cesium (a blocker of I<sub>f</sub>) induced spontaneous discharge in quiescent SAN through ThV<sub>os</sub>. In spontaneous SAN, Cs<sup>+</sup>increased V<sub>os </sub>and ThV<sub>os</sub>, thereby increasing the rate. Cs<sup>+ </sup>did not hinder the positive chronotropic action of NE. Barium increased the rate, as Cs<sup>+ </sup>did.</p> <p>Conclusion</p> <p>Adrenergic agonists: (i) initiate SAN discharge by decreasing the resting potential and inducing ThV<sub>os</sub>; (ii) gradually accelerate SAN rate by predominantly increasing size and slope of earlier and more negative ThV<sub>os</sub>; (iii) can induce sudden fast rhythms through the abrupt fusion of large V<sub>os </sub>with large ThV<sub>os</sub>; (iv) increase V<sub>os </sub>and ThV<sub>os</sub>by increasing cellular calcium; and (v) do not modify the oscillatory potentials by means of the hyperpolarization-activated current I<sub>f</sub>. The results provide evidence for novel mechanisms by which the SAN dominant pacemaker activity is initiated and enhanced by adrenergic agonists.</p> |
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| id | doaj.art-982ce11eb45441e7b446deb46b228b78 |
| institution | Directory Open Access Journal |
| issn | 1021-7770 1423-0127 |
| language | English |
| last_indexed | 2024-04-13T00:19:16Z |
| publishDate | 2009-01-01 |
| publisher | BMC |
| record_format | Article |
| series | Journal of Biomedical Science |
| spelling | doaj.art-982ce11eb45441e7b446deb46b228b782022-12-22T03:10:50ZengBMCJournal of Biomedical Science1021-77701423-01272009-01-01161101Essential role of diastolic oscillatory potentials in adrenergic control of guinea pig sino-atrial node dischargeVassalle MarioCatanzaro JohnNett MichaelRota Marcello<p>Abstract</p> <p>Background</p> <p>The diastolic oscillatory after-potential V<sub>os </sub>and pre-potential ThV<sub>os </sub>play an essential role in the pacemaker mechanism of sino-atrial node (SAN). The aim of this study was to investigate whether these oscillatory potentials are also involved in adrenergic control of SAN discharge.</p> <p>Methods</p> <p>V<sub>os </sub>and ThV<sub>os </sub>were visualized by superfusing guinea pig SAN in high [K<sup>+</sup>]<sub>o</sub>. The actions of adrenergic agonists on oscillatory potentials were studied by means of a microelectrode technique. Statistical significance was determined by means of Student's paired <it>t</it>-test.</p> <p>Results</p> <p>In non-spontaneous SAN, norepinephrine (NE) decreased the resting potential into a voltage range ("oscillatory zone") where increasingly larger ThV<sub>os </sub>appeared and initiated spontaneous discharge. In slowly discharging SAN, NE gradually increased the rate by increasing the amplitude and slope of earlier-occurring ThV<sub>os </sub>and of V<sub>os </sub>until these oscillations fused with initial diastolic depolarization (DD<sub>1</sub>). In the presence of NE, sudden fast rhythms were initiated by large V<sub>os </sub>that entered a more negative oscillatory zone and initiated a large ThV<sub>os</sub>. Recovery from NE exposure involved the converse changes. The β-adrenergic agonist isoproterenol had similar actions. Increasing calcium load by decreasing high [K<sup>+</sup>]<sub>o</sub>, by fast drive or by recovery in Tyrode solution led to growth of V<sub>os </sub>and ThV<sub>os </sub>which abruptly fused when a fast sudden rhythm was induced. Low [Ca<sup>2+</sup>]<sub>o </sub>antagonized the adrenergic actions. Cesium (a blocker of I<sub>f</sub>) induced spontaneous discharge in quiescent SAN through ThV<sub>os</sub>. In spontaneous SAN, Cs<sup>+</sup>increased V<sub>os </sub>and ThV<sub>os</sub>, thereby increasing the rate. Cs<sup>+ </sup>did not hinder the positive chronotropic action of NE. Barium increased the rate, as Cs<sup>+ </sup>did.</p> <p>Conclusion</p> <p>Adrenergic agonists: (i) initiate SAN discharge by decreasing the resting potential and inducing ThV<sub>os</sub>; (ii) gradually accelerate SAN rate by predominantly increasing size and slope of earlier and more negative ThV<sub>os</sub>; (iii) can induce sudden fast rhythms through the abrupt fusion of large V<sub>os </sub>with large ThV<sub>os</sub>; (iv) increase V<sub>os </sub>and ThV<sub>os</sub>by increasing cellular calcium; and (v) do not modify the oscillatory potentials by means of the hyperpolarization-activated current I<sub>f</sub>. The results provide evidence for novel mechanisms by which the SAN dominant pacemaker activity is initiated and enhanced by adrenergic agonists.</p>http://www.jbiomedsci.com/content/16/1/101 |
| spellingShingle | Vassalle Mario Catanzaro John Nett Michael Rota Marcello Essential role of diastolic oscillatory potentials in adrenergic control of guinea pig sino-atrial node discharge Journal of Biomedical Science |
| title | Essential role of diastolic oscillatory potentials in adrenergic control of guinea pig sino-atrial node discharge |
| title_full | Essential role of diastolic oscillatory potentials in adrenergic control of guinea pig sino-atrial node discharge |
| title_fullStr | Essential role of diastolic oscillatory potentials in adrenergic control of guinea pig sino-atrial node discharge |
| title_full_unstemmed | Essential role of diastolic oscillatory potentials in adrenergic control of guinea pig sino-atrial node discharge |
| title_short | Essential role of diastolic oscillatory potentials in adrenergic control of guinea pig sino-atrial node discharge |
| title_sort | essential role of diastolic oscillatory potentials in adrenergic control of guinea pig sino atrial node discharge |
| url | http://www.jbiomedsci.com/content/16/1/101 |
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