title: Refractoriness of the sheep superior vena cava myocardial sleeve.
abstract: The cardiomyocytes in the superior vena cava (SVC) myocardial sleeve have distinct action potentials and ionic current profiles, but the refractoriness of these cells has not been reported. Using standard intracellular microelectrode techniques, we demonstrated in sheep that the effective refractory period (ERP) of the cardiomyocytes in the SVC (114.7 +/- 6.5 ms) is shorter than that in the inferior vena cava (IVC) (166.7 +/- 6.2 ms), right atrial free wall (RAFW) (201.0 +/- 6.0 ms) and right atrial appendage (RAA) (203.1 +/- 5.8 ms) (P < 0.05). The right atrial cardiomyocyte ERP was heterogeneously shortened by acetylcholine, a muscarinic type 2 receptor (M(2)R) agonist. After perfusion with 15 microM acetylcholine, the shortest ERP occurred in the SVC (the ERP in the SVC, IVC, RAFW and RAA was 53.6 +/- 2.7, 98.9 +/- 2.2, 121.8 +/- 6.0 and 109.7 +/- 5.1 ms, respectively; P < 0.05). Carbachol (1 microM), another M(2)R agonist, produced a similar effect as acetylcholine. Furthermore, we used methoctramine, a M(2)R blocker, 4-DAMP, a muscarinic type 3 receptor (M(3)R) blocker, and tropicamide, a muscarinic type 4 receptor (M(4)R) blocker to inhibit the acetylcholine-induced ERP shortening of SVC cardiomyocytes, and found that the 50% inhibitory concentration for methoctramine, 4-DAMP and tropicamide was 5.91, 45.72 and 80.34 nM, respectively. Therefore, we conclude that the sheep SVC myocardial sleeve is a unique electrophysiological region of the right atrium with the shortest ERP both under physiological condition and under cholinergic agonist stimulation. M(2)R might play a major role in the response of the SVC myocardial sleeve to parasympathetic nerve tone. The association between the distinct refractoriness in SVC and atrial fibrillation originating from the region deserves further investigation.
authors.affiliation: Department of Cardiology, Tongji Hospital, Tongji University, Shanghai 200065, China.
authors.forename: Cuimei
authors.initials: C
authors.lastname: Zhao
authors.forename: Jie
authors.initials: J
authors.lastname: Qi
authors.forename: Xingyuan
authors.initials: X
authors.lastname: Liu
authors.forename: Huaizhi
authors.initials: H
authors.lastname: Chen
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.forename: Yi
authors.initials: Y
authors.lastname: Liu
authors.forename: Lei
authors.initials: L
authors.lastname: Liang
authors.forename: Yangyang
authors.initials: Y
authors.lastname: Zhang
authors.forename: Junjie
authors.initials: J
authors.lastname: Xiao
authors.forename: Li
authors.initials: L
authors.lastname: Li
authors.forename: Luying
authors.initials: L
authors.lastname: Peng
authors.forename: Jiahong
authors.initials: J
authors.lastname: Xu
authors.forename: Jun
authors.initials: J
authors.lastname: Ma
authors.forename: Ying
authors.initials: Y
authors.lastname: Yang
authors.forename: Xianzheng
authors.initials: X
authors.lastname: Wu
authors.forename: Yi-Han
authors.initials: YH
authors.lastname: Chen
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D003959:Diamines / Q000494:pharmacology; D022062:Electrophysiologic Techniques, Cardiac; D066298:In Vitro Techniques; D008839:Microelectrodes; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009206:Myocardium / Q000166:cytology*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000502:physiology*; D010880:Piperidines / Q000494:pharmacology; D012031:Refractometry; D012756:Sheep / Q000033:anatomy & histology*; D014331:Tropicamide / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology; D014683:Vena Cava, Superior / Q000166:cytology* / Q000187:drug effects
chemical_list: D018679:Cholinergic Agonists; D003959:Diamines; D018727:Muscarinic Antagonists; D010880:Piperidines; D014665:Vasodilator Agents; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium; D002217:Carbachol; D014331:Tropicamide; D000109:Acetylcholine; C054938:methoctramine