Jordi Heijman1, Dorit Kirchner2, Franziska Kunze2, Eva Maria Chrétien2, Martina B Michel-Reher3, Niels Voigt4, Michael Knaut5, Martin C Michel3, Ursula Ravens6, Dobromir Dobrev7. 1. Institute of Pharmacology, West German Heart and Vascular Center, Faculty of Medicine, University Duisburg-Essen, Essen, Germany; Department of Cardiology, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands. 2. Department of Pharmacology and Toxicology, Carl Gustav Carus Medical Faculty, Dresden University of Technology, Dresden, Germany. 3. Department of Pharmacology, Johannes Gutenberg University, Mainz, Germany. 4. Institute of Pharmacology, West German Heart and Vascular Center, Faculty of Medicine, University Duisburg-Essen, Essen, Germany. 5. Heart Surgery, Heart Center Dresden, Carl Gustav Carus Medical Faculty, Dresden University of Technology, Dresden, Germany. 6. Department of Pharmacology and Toxicology, Carl Gustav Carus Medical Faculty, Dresden University of Technology, Dresden, Germany; Institute of Experimental Cardiovascular Medicine, University Heart Center Freiburg-Bad Krozingen, Freiburg, Germany. 7. Institute of Pharmacology, West German Heart and Vascular Center, Faculty of Medicine, University Duisburg-Essen, Essen, Germany; Department of Pharmacology and Toxicology, Carl Gustav Carus Medical Faculty, Dresden University of Technology, Dresden, Germany. Electronic address: Dobromir.Dobrev@uk-essen.de.
Abstract
BACKGROUND: Basal and acetylcholine-gated inward-rectifier K+-currents (IK1 and IK,ACh, respectively) are altered in atrial fibrillation (AF). Gi-protein-coupled muscarinic (M) receptors type-2 are considered the predominant receptors activating IK,ACh. Although a role for Gq-coupled non-M2-receptor subtypes has been suggested, the precise regulation of IK,ACh by multiple M-receptor subtypes in the human atrium is unknown. Here, we investigated M1-receptor-mediated IK,ACh regulation and its remodeling in chronic AF (cAF). METHODS AND RESULTS: M1-receptor mRNA and protein abundance were increased in atrial cardiomyocyte fractions and atrial homogenates from cAF patients, whereas M2-receptor levels were unchanged. The regulation of IK,ACh by M1-receptors was investigated in right-atrial cardiomyocytes using two applications of the M-receptor agonist carbachol (CCh, 2μM), with pharmacological interventions during the second application. CCh application produced a rapid current increase (Peak-IK,ACh), which declined to a quasi-steady-state level (Qss-IK,ACh). In sinus rhythm (Ctl) the selective M1-receptor antagonists pirenzepine (10nM) and muscarinic toxin-7 (MT-7, 10nM) significantly inhibited CCh-activated Peak-IK,ACh, whereas in cAF they significantly reduced both Peak- and Qss-IK,ACh, with no effects on basal inward-rectifier currents in either group. Conversely, the selective M1-receptor agonist McN-A-343 (100μM) induced a current similar to the CCh-activated current in Ctl atrial cardiomyocytes pretreated with pertussis toxin to inhibit M2-receptor-mediated Gi-protein signaling, which was abolished by MT-7. Computational modeling indicated that M1- and M2-receptors redundantly activate IK,ACh to abbreviate APD, albeit with predominant effects of M2-receptors. CONCLUSION: Our data suggest that Gq-coupled M1-receptors also regulate human atrial IK,ACh and that their relative contribution to IK,ACh activation is increased in cAF patients. We provide novel insights about the role of non-M2-receptors in human atrial cardiomyocytes, which may have important implications for understanding AF pathophysiology.
BACKGROUND: Basal and acetylcholine-gated inward-rectifier K+-currents (IK1 and IK,ACh, respectively) are altered in atrial fibrillation (AF). Gi-protein-coupled muscarinic (M) receptors type-2 are considered the predominant receptors activating IK,ACh. Although a role for Gq-coupled non-M2-receptor subtypes has been suggested, the precise regulation of IK,ACh by multiple M-receptor subtypes in the human atrium is unknown. Here, we investigated M1-receptor-mediated IK,ACh regulation and its remodeling in chronic AF (cAF). METHODS AND RESULTS: M1-receptor mRNA and protein abundance were increased in atrial cardiomyocyte fractions and atrial homogenates from cAFpatients, whereas M2-receptor levels were unchanged. The regulation of IK,ACh by M1-receptors was investigated in right-atrial cardiomyocytes using two applications of the M-receptor agonist carbachol (CCh, 2μM), with pharmacological interventions during the second application. CCh application produced a rapid current increase (Peak-IK,ACh), which declined to a quasi-steady-state level (Qss-IK,ACh). In sinus rhythm (Ctl) the selective M1-receptor antagonists pirenzepine (10nM) and muscarinic toxin-7 (MT-7, 10nM) significantly inhibited CCh-activated Peak-IK,ACh, whereas in cAF they significantly reduced both Peak- and Qss-IK,ACh, with no effects on basal inward-rectifier currents in either group. Conversely, the selective M1-receptor agonist McN-A-343 (100μM) induced a current similar to the CCh-activated current in Ctl atrial cardiomyocytes pretreated with pertussis toxin to inhibit M2-receptor-mediated Gi-protein signaling, which was abolished by MT-7. Computational modeling indicated that M1- and M2-receptors redundantly activate IK,ACh to abbreviate APD, albeit with predominant effects of M2-receptors. CONCLUSION: Our data suggest that Gq-coupled M1-receptors also regulate human atrial IK,ACh and that their relative contribution to IK,ACh activation is increased in cAFpatients. We provide novel insights about the role of non-M2-receptors in human atrial cardiomyocytes, which may have important implications for understanding AF pathophysiology.
Authors: Magdolna Levay; Kurt Allen Krobert; Karola Wittig; Niels Voigt; Marcel Bermudez; Gerhard Wolber; Dobromir Dobrev; Finn Olav Levy; Thomas Wieland Journal: J Pharmacol Exp Ther Date: 2013-07-25 Impact factor: 4.030
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