Regular mild exercise is recommended to the general population as beneficial to health. Regular exercise typically leads to structural and electrical remodelling of the heart but in human studies it is difficult to relate the extrinsic and intrinsic influences on intact hearts to changes seen at the single cell level. In this study we wished to test whether changes in electrical activity in intact hearts, in response to voluntary wheel running exercise training, were consistent with our previous observations in single cardiac myocytes and whether these changes resulted in altered susceptibility to arrhythmic stimuli. Female rats performed 5 weeks of voluntary wheel running. Implanted telemetry transmitters were used to measure electrocardiograms (ECGs) and determine heart rate variability (HRV) in conscious, unrestrained, trained (TRN) and sedentary (SED) animals. In isolated hearts, left ventricular epicardial monophasic action potentials (MAPs) were recorded and the responses to potentially arrhythmic interventions were assessed. Exercise training caused cardiac hypertrophy, as indexed by a significantly greater heart weight to body weight ratio. Consistent with previous measurements of action potential duration in single myocytes, MAPs were significantly longer at 50%, 75% and 90% repolarization. Arrhythmic susceptibility was not different between SED and TRN hearts. Trained animals displayed significantly altered HRV by week 5, in a manner consistent with reduced sympathetic tone, however resting ECG parameters, including those most associated with repolarisation duration, were unaltered. We conclude that intrinsic changes to cellular cardiac electrophysiology, induced by mild voluntary exercise, are not attenuated by the electronic loading that occurs in intact hearts. However, in vivo, extrinsic neuro-hormonal control of the heart may minimize the effects of intrinsic alterations in electrical activity.

中文翻译：

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雌性大鼠自愿运动诱发的离体心脏和体内心脏电活动变化的比较

建议普通人群定期进行轻度运动，因为这对健康有益。定期运动通常会导致心脏的结构和电重构，但是在人体研究中，很难将对完整心脏的外在和内在影响与单细胞水平的变化联系起来。在这项研究中，我们希望测试完整的心脏在自愿轮式运动训练后的电活动变化是否与我们先前在单个心肌细胞中的观察结果一致，以及这些变化是否导致对心律不齐刺激的敏感性改变。雌性大鼠进行5周的自愿轮转。植入式遥测变送器用于测量心电图（ECG）并确定有意识的，不受约束的，受训（TRN）和久坐（SED）的动物。在离体心脏中，记录左心室心外膜单相动作电位（MAPs）并评估对潜在心律不齐干预的反应。运动训练引起心脏肥大，其通过明显更大的心脏重量与体重比来指示。与先前对单个肌细胞动作电位持续时间的测量结果一致，MAP在50％，75％和90％复极化时明显更长。SED和TRN心脏之间的心律失常敏感性没有差异。受过训练的动物在第5周时表现出明显的HRV改变，与交感神经张力降低相一致，但是静止的ECG参数（包括与复极化持续时间最相关的那些参数）并未改变。我们得出结论，细胞心脏电生理的内在变化，轻度的自愿运动引起的心电图不能被完整心脏中发生的电子负载减弱。然而，在体内，心脏的外在神经激素控制可以使电活动中内在改变的影响最小化。