Abstract

The heart of jawless fish (Cyclostomata; lamprey, hagfish) and jawed fish (Teleostei) is homologous to the heart of higher vertebrates. A study of this organ in archaic Cyclostomata and Teleostei, which are different in their evolutionary “ages”, genetic characteristics and hypoxia tolerance, is of particular interest in the search for the factors that determine myocardial resistance to oxygen deficiency. Cyclostomata and Teleostei share the same branchial type of respiration and the presence of only one circle of blood circulation. The principal contractile organ that provides blood circulation, the branchial heart, consists of two chambers. Hagfish make up the oldest class of extant vertebrates whose circulation is maintained by the non-innervated (aneural) branchial heart and three sets of accessory “hearts”. Lampreys are the first vertebrates whose heart receives innervation from the vagus nerve. In turn, Teleostei are the first to receive sympathetic innervation of the heart from the vagosympathetic trunks. In the heart of Cyclostomata and Teleostei, no signs of the cardiac conduction system similar to that in higher vertebrates were found, which does not negate the existence of a well-coordinated mechanism for the propagation of myocardial excitation–contraction coupling. The mechanism of heart rhythm generation links the electrical processes that arise in the myocardium with the expression of hyperpolarization-activated cyclic nucleotide-gated channels (HCN channels). In the heart of hagfish and teleosts, six isoforms of HCN channels are expressed. The regulated distribution density of HCN channels in the myocardium may be a precursor of the cardiac conduction system which characterizes higher vertebrates. The expression of the three cardiac HCN isoforms (HCN2, HCN3 and HCN4) in such a relict taxon as hagfish suggests their presence in the myocardium of the common ancestor of vertebrates before the divergence with Myxiniformes. This may also suggest a particular significance of HCN2, HCN3 and HCN4 in the formation of cardiac activity at the time of the emergence of a multi-chambered myogenic heart. It is assumed that the evolutionary progress in the archaic groups of primitive vertebrates was aimed at the “creation” of a faster effector system for the regulation of cardiac activity and dual (excitatory/inhibitory) control of myocardial functions.

中文翻译：

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下颚和下颚鱼心脏的解剖和生理特殊性

摘要

无颚鱼（Cyclostomata；七lamp鳗，ha鱼）和颚鱼（Teleostei）的心脏与高级脊椎动物的心脏同源。在古老的Cyclostomata和Teleostei中对该器官的研究，其进化“年龄”，遗传特征和低氧耐受性不同，对于寻找确定心肌对缺氧抵抗力的因素特别感兴趣。Cyclostomata和Teleostei共享相同的分支呼吸形式，并且只有一个循环的血液循环。提供血液循环的主要收缩器官是branch门心脏，由两个腔室组成。g鱼是现存脊椎动物中最古老的一类，其流通由无神经的（神经性的）分支心脏和三组附属的“心脏”维持。七rey鳗是最早接受心脏从迷走神经支配的脊椎动物。反过来，Teleostei是第一个从迷走神经交感神经干接受交感神经支配的人。在Cyclostomata和Teleostei的中心，没有发现与高等脊椎动物相似的心脏传导系统的迹象，这并不排除存在一个协调良好的机制来促进心肌兴奋-收缩耦合的传播。心律发生的机制将心肌中发生的电过程与超极化激活的环状核苷酸门控通道（HCN通道）的表达联系起来。在ha鱼和硬骨鱼的心脏中，表达了六种HCN通道亚型。心肌中HCN通道的调节分布密度可能是心脏传导系统的前兆，其特征是较高等的脊椎动物。三种心脏HCN亚型（HCN2，粘虫形。这也可能表明在多腔成肌心脏出现时，HCN2，HCN3和HCN4在心脏活动形成中具有特殊意义。据推测，原始脊椎动物古体中的进化进展旨在“创造”一个更快的效应器系统，以调节心脏活动和心肌功能的双重（兴奋性/抑制性）控制。