Pacemaker actions in the turtle heart

Lange, Gertrude; Hh, Lu; Tsumuraya, Y; Brooks, CM

doi:10.1152/ajplegacy.1966.210.6.1375

Cited by 5 publications

(3 citation statements)

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“…Based on [4,10,20,27,28,30,[39][40][41][42][43][44][45][46][47][48][49][50] Most studies in ectothermic vertebrates show that the dominant pacemaker activity is located at the sinuatrial junction, albeit that an anatomical sinus node is absent [20,21,35,37,55,56]. In addition, some studies report pacemaking upstream of the sinuatrial junction at variable positions [53,57], and the dominant pacemaker activity of the heart of man may shift within the sinus node region [29,58,59]. This resembles the embryonic stages of mouse and chicken, where dominant pacemaker activity is not yet confined to the sinus node, as underlined by the broad expression of the sodium channels related to spontaneous depolarization, like Hcn4 [60][61][62][63][64][65].…”

Section: The Dominant Pacemaker Generally Is Located At the Sinuatriamentioning

confidence: 99%

Evolution of the Sinus Venosus from Fish to Human

Jensen

Boukens

Wang

et al. 2014

JCDD

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The sinus venosus, the cardiac chamber upstream of the (right) atrium, is a severely underinvestigated structure. Yet, its myocardium harbors the cardiac pacemaker in all vertebrates. In human, ectopic pacemaking and subsequent pathologies may originate from sinus venosus-derived myocardium surrounding the coronary sinus and the superior caval vein. In ectothermic vertebrates, i.e., fishes, amphibians and reptiles, the sinus venosus aids atrial filling by contracting prior to the atrium (atria). This is facilitated by the sinuatrial delay of approximately the same duration as the atrioventricular delay, which facilitates atrial filling of the ventricles. In mammals, the sinuatrial delay is lost, and the sinus venosus-derived myocardium persists as an extensive myocardial sheet surrounding the caval veins, which is activated in synchrony with the myocardium of the atria. The caval vein myocardium is hardly of significance in the healthy formed heart, but we suggest that the sinus venosus functions as a chamber during development when cardiac output, heart rate, blood pressure and architecture is much more like that of ectothermic vertebrates. The remodeling of the sinus venosus in mammals may be an adaptation associated with the high heart rates necessary for postnatal endothermy. If so, the endothermic birds should exhibit a similar remodeling as mammals, which remains to be investigated.

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Section: The Dominant Pacemaker Generally Is Located At the Sinuatriamentioning

confidence: 99%

Evolution of the Sinus Venosus from Fish to Human

Jensen

Boukens

Wang

et al. 2014

JCDD

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“…The heartbeat of ectothermic vertebrates is driven by a pacemaker within the sinus venosus, the myocardium upstream of the right atrium 1 . This pacemaker is not anatomically identifiable and electrophysiological studies suggest that the position of the pacemaker within the sinus venosus may differ between species 2 – 5 . In mammals and birds, the pacemaker resides within an anatomically distinguishable structure, the sinus node, positioned at the sinuatrial junction 6 , 7 .…”

Section: Introductionmentioning

confidence: 99%

Morpho-functional characterization of the systemic venous pole of the reptile heart

Jensen

Vesterskov

Boukens

et al. 2017

Sci Rep

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Mammals evolved from reptile-like ancestors, and while the mammalian heart is driven by a distinct sinus node, a sinus node is not apparent in reptiles. We characterized the myocardial systemic venous pole, the sinus venosus, in reptiles to identify the dominant pacemaker and to assess whether the sinus venosus remodels and adopts an atrium-like phenotype as observed in mammals. Anolis lizards had an extensive sinus venosus of myocardium expressing Tbx18. A small sub-population of cells encircling the sinuatrial junction expressed Isl1, Bmp2, Tbx3, and Hcn4, homologues of genes marking the mammalian sinus node. Electrical mapping showed that hearts of Anolis lizards and Python snakes were driven from the sinuatrial junction. The electrical impulse was delayed between the sinus venosus and the right atrium, allowing the sinus venosus to contract and aid right atrial filling. In proximity of the systemic veins, the Anolis sinus venosus expressed markers of the atrial phenotype Nkx2-5 and Gja5. In conclusion, the reptile heart is driven by a pacemaker region with an expression signature similar to that of the immature sinus node of mammals. Unlike mammals, reptiles maintain a sinuatrial delay of the impulse, allowing the partly atrialized sinus venosus to function as a chamber.

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“…The internal architecture of the atrium was remarkable in the presence of pectinate muscles attaching to the SA valve. It has been shown that pacemaker cells are located adjacent to the SA valve in the vertebrate heart (Keith and Flack, 1907;Lange et al, 1966;van Mierop, 1967;Komuro et al, 1986;Haverinen and Vornanen, 2007;Tessadori et al, 2012). Furthermore, pectinate muscles in the chick embryo form the conduction pathway (Sedmera et al, 2006).…”

Section: Architecture Of the Atriummentioning

confidence: 99%

Heart Anatomy of Rhincodon typus: Three‐Dimensional X‐Ray Computed Tomography of Plastinated Specimens

Hirasaki

Tomita

Yanagisawa

et al. 2018

The Anatomical Record

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In this study, we examined the structure of the heart of the whale shark, Rhincodon typus, using a plastination technique and three‐dimensional X‐ray computer tomography (3DCT). Inspection of the atrium revealed a symmetric distribution of the pectinate muscles attached to the commissures of the sino‐atrial valve, suggesting some functional advantages. The majority of the ventricular wall comprised spongiosa, and compacta accounted for only ~3% of the entire thickness. There were three major fiber orientations in the spongiosa: the fibers on the endocardial side formed trabeculae that were aligned with the blood flow tract, whereas those on the epicardial side formed a circular pattern around the flow tract. Transmural myofibers connected the inner and outer layers in the spongiosa, which may serve as an intraventricular conduction pathway. Plastination and 3DCT is a powerful combination that allowed for multifaceted visualization of the internal structure of rare heart specimens in a nondestructive manner. Anat Rec, 301:1801–1808, 2018. © 2018 Wiley Periodicals, Inc.

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Pacemaker actions in the turtle heart

Cited by 5 publications

References 0 publications

Evolution of the Sinus Venosus from Fish to Human

Evolution of the Sinus Venosus from Fish to Human

Morpho-functional characterization of the systemic venous pole of the reptile heart

Heart Anatomy of Rhincodon typus: Three‐Dimensional X‐Ray Computed Tomography of Plastinated Specimens

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