Abstract：
Amphibians are a classical object for physiological studies, and they are of great value for developmental studies owing to their transition from an aquatic larval form to an adult form with a terrestrial lifestyle. Axolotls (Ambystoma mexicanum) are of special interest for such studies because of their neoteny and facultative pedomorphosis, as in these animals, metamorphosis can be induced and fully controlled in laboratory conditions. It has been suggested that their metamorphosis, associated with gross anatomical changes in the heart, also involves physiological and electrical remodeling of the myocardium. We used whole-cell patch clamp to investigate possible changes caused by metamorphosis in electrical activity and major ionic currents in cardiomyocytes isolated from paedomorphic and metamorphic axolotls. T4-induced metamorphosis caused shortening of atrial and ventricular action potentials (APs), with no changes in resting membrane potential or maximum velocity of AP upstroke, favoring higher heart rate possible in metamorphic animals. Potential-dependent potassium currents in axolotl myocardium were represented by delayed rectifier currents IKr and IKs, and upregulation of IKs caused by metamorphosis probably underlies AP shortening. Metamorphosis was associated with downregulation of inward rectifier current IK1, probably serving to increase the excitability of myocardium in metamorphic animals. Metamorphosis also led to a slight increase in fast sodium current INa with no changes in its steady-state kinetics and to a significant upregulation of ICa in both atrial and ventricular cells, indicating stronger Ca2+ influx for higher cardiac contractility in metamorphic salamanders. Taken together, these changes serve to increase cardiac reserve in metamorphic animals.
摘要：
两栖动物是生理研究的经典对象，由于它们从水生幼虫形式过渡到具有陆生生活方式的成虫形式，因此对发育研究具有重要价值。Axolotls（Ambystomamexicanum）由于其新生性和兼性性花样形态而对此类研究特别感兴趣，就像这些动物一样，在实验室条件下可以诱导和完全控制变态。有人认为它们的变态，与心脏的大体解剖变化有关，还涉及心肌的生理和电重塑。我们使用全细胞膜片钳研究了从拟态和变态轴突中分离出的心肌细胞的电活动和主要离子电流的变态引起的可能变化。T4引起的变态导致心房和心室动作电位（AP）缩短，静息膜电位或AP上冲程的最大速度没有变化，有利于变态动物的心率更高。axolotl心肌中的电位依赖性钾电流由延迟整流电流IKr和IKs表示，变态引起的IKs上调可能是AP缩短的基础。变态与向内整流电流IK1的下调有关，可能有助于增加变态动物心肌的兴奋性。变态还导致快速钠电流INa的轻微增加，其稳态动力学没有变化，并且在心房和心室细胞中ICa的显着上调。表明在变态sal中，Ca2流入越强，心脏收缩力越高。一起来看,这些变化有助于增加变态动物的心脏储备。
