title: Muscarinic stimulation and pinacidil produce similar facilitation of tachyarrhythmia induction in rat isolated atria.
abstract: Atrial tachyarrhythmias, the most common type of cardiac arrhythmias, are associated with greater stroke risk. Muscarinic cholinergic agonists have been shown to facilitate atrial tachyarrhythmia maintenance in the absence of cardiac disease. This has been attributed to action potential shortening, which enhances myocardial electrical anisotropy, and thus creates a substrate for reentrant excitation. In this study, we describe a similar effect of the ATP-sensitive K(+) channel (KATP) opener pinacidil on tachyarrhythmia induction in isolated rat atria. Pinacidil, which activates a weakly inwardly-rectifying current in isolated atrial myocytes, enhanced arrhythmia induction in the right and left atria. This effect was abolished by the KATP blocker glibenclamide, but not by atropine, which rules out a possible indirect effect due to stimulation of acetylcholine release. However, pinacidil attenuated carbachol-induced tachyarrhythmia facilitation, which may indicate that the action of these agonists converges to a common cellular mechanism. Both agonists caused marked action potential shortening in isolated atrial myocytes. Moreover, during arrhythmia in the presence of pinacidil and carbachol, the atrial vectorelectrographic patterns were similar and consistent with reentrant propagation of the electrical activity. From these results, we conclude that the KATP channel opening is pro-arrhythmic in atrial tissue, which may pose as an additional risk in the scenario of myocardial hypoxia. Moreover, the similarity of the electrophysiological effects of pinacidil and carbachol is suggestive that the sole increase in background K(+) conductance is sufficient for atrial tachyarrhythmia facilitation.
authors.affiliation: Department of Biomedical Engineering/FEEC, University of Campinas, Caixa Postal 6040, 13084-971 Campinas, SP, Brazil. Electronic address: profnivaldo@fiap.com.br.
authors.forename: Nivaldo
authors.initials: N
authors.lastname: Zafalon
authors.forename: Natália F
authors.initials: NF
authors.lastname: Oshiyama
authors.forename: José W M
authors.initials: JW
authors.lastname: Bassani
authors.forename: Rosana A
authors.initials: RA
authors.lastname: Bassani
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D006325:Heart Atria / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000473:pathology / Q000503:physiopathology*; D066298:In Vitro Techniques; D008297:Male; D018721:Muscarinic Agonists / Q000494:pharmacology*; D020110:Pinacidil / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D012849:Sinoatrial Node / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology; D013610:Tachycardia / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D014463:Ultrasonography
chemical_list: D018721:Muscarinic Agonists; D020110:Pinacidil
keywords: 3′-5′ cyclic adenosine monophosphate; ACh; AP; APD; AR; AT; ATP-sensitive K(+) channel; ATP-sensitive K(+) current; Action potential; Atrial tachyarrhythmia; CCh; Electrical propagation; High; I(K(ACh)); I(K(ATP)); Inward rectifier potassium currents; K(ATP) channel; Low; SUR; TI; V(m); acetylcholine; acetylcholine-regulated K(+) current; action potential; action potential duration; atrial tachyarrhythmia; cAMP; carbachol; high-inducibility stimulation protocol; low-inducibility stimulation protocol; membrane potential; right atrial spontaneous rate; sulfonylurea receptor; tachyarrhythmia induction index