The inverse relationship between muscle stress and cross-sectional area in cardiac preparations has repeatedly been reported in intact twitching muscles. However, the critical muscle size at which diffusion-limited delivery of oxygen begins to compromise muscle stress development is smaller than what is predicted by a mathematical model of muscle oxygenation. In a twitching muscle, while oxygenation is vital, muscle stress production is modulated by a number of other cellular processes including contractile activation and mitochondrial respiration. The objective of this study is to investigate whether these two factors can reconcile the discrepancy between predicted and observed critical muscle sizes. In a paired experimental design, we have subjected intact rat right-ventricular trabeculae of various sizes to electrical stimulation at 2 Hz followed by either barium contracture to maximise contractile activation, or calcium contracture following muscle permeabilisation to directly supply ATP in order to obviate mitochondrial respiration. We found that the inverse relationship between muscle stress and cross-sectional area was preserved in both of these contracture modes. While, in both cases, the stresses were higher than those from twitching trabeculae, owing to higher levels of muscle activation, there was only a small increase in the critical muscle size at which stress begins to decline. Our findings show that neither contractile activation nor mitochondrial respiration contributes significantly to the discrepancy between predicted and reported critical muscle sizes. Nevertheless, what is revealing is that the inverse relation between stress and muscle size in intact twitching muscles was also obtained in muscles subjected to barium and calcium contracture.

中文翻译：

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在 Ba2+ 挛缩和化学渗透性 Ca2+ 挛缩中保留心脏肌肉应力与横截面积之间的反比关系

在完整的抽搐肌肉中反复报道了心脏制剂中肌肉应力与横截面积之间的反比关系。然而，扩散限制的氧气输送开始损害肌肉压力发展的临界肌肉尺寸小于肌肉氧合数学模型预测的尺寸。在抽搐的肌肉中，虽然氧合作用至关重要，但肌肉压力的产生受到许多其他细胞过程的调节，包括收缩激活和线粒体呼吸。本研究的目的是调查这两个因素是否可以调和预测和观察到的临界肌肉尺寸之间的差异。在配对实验设计中，我们已经对不同大小的完整大鼠右心室小梁进行了 2 Hz 的电刺激，然后是钡挛缩以最大化收缩激活，或在肌肉透化后钙挛缩以直接供应 ATP 以消除线粒体呼吸。我们发现，在这两种挛缩模式中，肌肉应力与横截面积之间的反比关系得以保留。虽然在这两种情况下，压力都高于抽动小梁的压力，但由于肌肉激活水平较高，压力开始下降的临界肌肉尺寸仅略有增加。我们的研究结果表明，收缩激活和线粒体呼吸都不会显着导致预测和报告的关键肌肉尺寸之间的差异。