Diffee Gary M, Nagle Daniel F
Department of Kinesiology, University of Wisconsin, Madison, WI 53706, USA.
J Appl Physiol (1985). 2003 Jul;95(1):35-42. doi: 10.1152/japplphysiol.00951.2002. Epub 2003 Jan 24.
Myocardial function is enhanced by endurance exercise training, but the cellular mechanisms underlying this improved function remain unclear. A number of studies have shown that the characteristics of cardiac myocytes vary across the width of the ventricular wall. We have previously shown that endurance exercise training alters the Ca2+ sensitivity of tension as well as contractile protein isoform expression in rat cardiac myocytes. We tested the hypothesis that these effects of training are not uniform across the ventricular wall but are more pronounced in the subendocardial (Endo) region of the myocardium. Female Sprague-Dawley rats were divided into sedentary control (C) and exercise trained (T) groups. T rats underwent 11 wk of progressive treadmill exercise. Myocytes were isolated from the Endo region of the myocardium and from the subepicardial (Epi) region of both T and C hearts. We found an increase in the Ca2+ sensitivity of tension in T cells compared with C cells, but this difference was larger in the Endo cells than in the Epi cells. In addition, we found a training-induced increase in atrial myosin light chain 1 (aMLC1) expression that was larger in the Endo compared with Epi samples. We conclude that effects of exercise training on myocyte contractile and biochemical properties are greater in myocytes from the Endo region of the myocardium than those from the Epi region. In addition, these results provide evidence that the increase in aMLC1 expression may be responsible for some of the training-induced increase in myocyte Ca2+ sensitivity of tension.
耐力运动训练可增强心肌功能，但其功能改善背后的细胞机制仍不清楚。多项研究表明，心肌细胞的特性在心室壁宽度上存在差异。我们之前已经表明，耐力运动训练会改变大鼠心肌细胞中张力的Ca2+敏感性以及收缩蛋白亚型的表达。我们检验了这样一个假设，即训练的这些效应在心室壁上并非均匀一致，而是在心肌的内膜下（Endo）区域更为显著。将雌性Sprague-Dawley大鼠分为久坐对照组（C）和运动训练组（T）。T组大鼠进行了11周的递增式跑步机运动。从T组和C组心脏的心肌内膜下（Endo）区域以及心外膜下（Epi）区域分离出心肌细胞。我们发现，与C组细胞相比，T组细胞中张力的Ca2+敏感性增加，但这种差异在内膜下（Endo）细胞中比在心外膜下（Epi）细胞中更大。此外，我们发现训练诱导的心房肌球蛋白轻链1（aMLC1）表达增加，内膜下（Endo）样本中的增加幅度比心外膜下（Epi）样本中的更大。我们得出结论，运动训练对心肌细胞收缩和生化特性的影响在心肌内膜下（Endo）区域的细胞中比在心外膜下（Epi）区域的细胞中更大。此外，这些结果提供了证据，表明aMLC1表达的增加可能是训练诱导的心肌细胞张力Ca2+敏感性增加的部分原因。
