Résumé
Catecholamines increase the amplitudes of oscillatory afterpotentials (OAP) and peak magnitude of the transient inward current (Iti) responsible for OAP. The objectives of this study were to determine whether β-adrenoceptor stimulation can induce Iti, and to determine the mechanism by which β-adrenoceptor stimulation increases the magnitude of Iti. Experiments were performed using standard two electrode voltage-clamp techniques in isolated rabbit Purkinje fibers. Holding potential was either -50 or -80 mV. The Iti was elicited by repolarizing steps, following 1.5 or 3 s activating steps to potentials near 0 mV. Isoproterenol (ISO) failed to induce the Iti at concentrations from 10-8 to 10-6 m. However, ISO (10-7 m) significantly increased peak magnitude of spontaneously occurring Iti (P < 0.05), or Iti induced by acetylstrophanthidin (AS) (P < 0.05). ISO also shifted the minimum activation voltage 10 mV more negative (P < 0.05). The currentvoltage relationship demonstrated that ISO significantly increased the range of potentials over which Iti≥5 nA occurred, but did not significantly shift the voltage at which maximum peak current was observed. Effects of ISO on Iti were blocked by 10-7m propranolol or atenolol. Mn2+ (2 mm) or verapamil (2 μm) blocked the slow inward current (Isi) more than 80% before substantially decreasing peak Iti. Either agent blocked stimulation of Isi but not Iti by ISO at 10-7m. In contrast, quinacrine (20 μm), an inhibitor of Na+Ca2+ exchange, abolished stimulation of Iti by ISO while having no significant effect on Isi. Our results indicate that β-adrenoceptor stimulation cannot induce Iti in rabbit Purkinje fibers, but can enhance the Iti induced by other means, by stimulating Na+Ca2+ exchange.
Langue d'origine | English |
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Pages (de-à) | 551-562 |
Nombre de pages | 12 |
Journal | Journal of Molecular and Cellular Cardiology |
Volume | 23 |
Numéro de publication | 5 |
DOI | |
Statut de publication | Published - mai 1991 |
Note bibliographique
Funding Information:Please address all correspondence and reprint requests to: Gregory R. Ferrier, Department of Pharmacology, Charles Tupper medical building, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7 This study was supported in part by a grant from the Medical Research Council of Canada. X. Han is fellow of the Medical Research Council of Canada
ASJC Scopus Subject Areas
- Molecular Biology
- Cardiology and Cardiovascular Medicine
PubMed: MeSH publication types
- Journal Article
- Research Support, Non-U.S. Gov't