Simpson Jeremy A, Van Eyk Jennifer, Iscoe Steve
Department of Physiology, Queen's University, Kingston, Ontario, Canada K7L 3N6.
J Physiol. 2004 Feb 1;554(Pt 3):891-903. doi: 10.1113/jphysiol.2003.051318. Epub 2003 Dec 12.
To evaluate injury to respiratory muscles of rats breathing against an inspiratory resistive load, we measured the release into blood of a myofilament protein, skeletal troponin I (sTnI), and related this release to the time course of changes in arterial blood gases, respiratory drive (phrenic activity), and pressure generation. After approximately 1.5 h of loading, hypercapnic ventilatory failure occurred, coincident with a decrease in the ratio of transdiaphragmatic pressure to integrated phrenic activity (P(di)/ integral Phr) during sighs. This was followed at approximately 1.9 h by a decrease in the P(di)/ integral Phr ratio during normal loaded breaths (diaphragmatic fatigue). Loading was terminated at pump failure (a decline of P(di) to half of steady-state loaded values), approximately 2.4 h after load onset. During 30 s occlusions post loading, rats generated pressure profiles similar to those during occlusions before loading, with comparable blood gases, but at a higher neural drive. In a second series of rats, we tested for sTnI release using Western blot-direct serum analysis of blood samples taken before and during loading to pump failure. We detected only the fast isoform of sTnI, release beginning midway through loading. Differential detection with various monoclonal antibodies indicated the presence of modified forms of fast sTnI. The release of fast sTnI is consistent with load-induced injury of fast glycolytic fibres of inspiratory muscles, probably the diaphragm. Characterization of released fast sTnI may provide insights into the molecular basis of respiratory muscle dysfunction; fast sTnI may also prove useful as a marker of impending respiratory muscle fatigue.
为评估大鼠在对抗吸气性阻力负荷呼吸时呼吸肌的损伤情况，我们测量了肌丝蛋白——骨骼肌肌钙蛋白I（sTnI）释放入血的情况，并将这种释放与动脉血气、呼吸驱动（膈神经活动）和压力产生的变化时间进程相关联。负荷约1.5小时后，出现高碳酸血症性通气衰竭，同时叹气时跨膈压与膈神经活动积分的比值（P(di)/膈神经活动积分）下降。约1.9小时后，正常负荷呼吸时的P(di)/膈神经活动积分比值下降（膈肌疲劳）。在泵衰竭（P(di)降至稳态负荷值的一半）时终止负荷，负荷开始后约2.4小时出现泵衰竭。在负荷后30秒的阻塞期间，大鼠产生的压力曲线与负荷前阻塞期间相似，血气相当，但神经驱动更高。在第二组大鼠中，我们在负荷至泵衰竭前和期间采集血样，通过蛋白质印迹法直接分析血清来检测sTnI的释放情况。我们仅检测到sTnI的快速异构体，释放始于负荷过程的中途。用各种单克隆抗体进行差异检测表明存在快速sTnI的修饰形式。快速sTnI的释放与吸气肌（可能是膈肌）的快速糖酵解纤维的负荷诱导损伤一致。对释放的快速sTnI进行表征可能有助于深入了解呼吸肌功能障碍的分子基础；快速sTnI也可能被证明是即将发生的呼吸肌疲劳的有用标志物。
