FUNCTIONAL CHANGES IN DIAPHRAGMATIC FATIGUE

本申请中提出的实验的目的是提供一种 对减少的细胞机制有更清晰的理解 由于横隔膜暴露于酸中毒而产生的收缩力量。 最近，一些临床文献表明，慢性阻塞性肺疾病患者 高碳酸血症的阻塞性肺病患者不能发展为 吸气压力与同样受阻的优势症患者相同。 此外，最近在正常人身上进行的一项研究表明 人工诱导的高碳酸血症不仅减少了横隔膜 为给定的电输入产生的压力，但也设置了 更容易出现横隔膜疲劳。我们已经证明了这些 在体犬和体外大鼠的隔膜中相同的现象 横隔膜。 这项提议的总体假设是，急性和长期 细胞外酸中毒致大鼠体外机械功能障碍 通过以下一种或多种机制：抑制 细胞阳离子(Na-H)和阴离子(HCO3-C1)泵的调节能力 细胞内pH；通过抑制糖酵解消耗高能磷酸盐 或有氧酶；调节肌膜或细胞器钙的运输 或改变细胞内钙结合部位；引起去极化 静息的膜电位；改变乙酰胆碱的模式 在隔膜的神经肌肉交界处释放。其中一些 机制可能会非常负责，而其他机制可能会在一段时间后变得如此 时间的流逝。 该提案描述了四组将测试这些特性的实验 机械装置。31P核磁共振实验 将检验涉及酸中毒对隔膜影响的假说 胞内pH和高能磷酸盐含量。实验 使用基于14C和~3H标记葡萄糖的方法将 研究酸中毒对糖酵解和有氧代谢的影响。 对45个钙外流数据进行完整的动力学分析将允许 细胞钙转运过程的定量以及细胞内钙离子的变化 这些过程是由酸中毒引起的。最后是标准电生理 记录静息膜电位的技术将被使用 和微型端板电势。

The purpose of the experiment proposed in this application is to provide a clearer understanding of cellular mechanisms responsible for the decreased force of contraction developed by the diaphragm exposed to acidosis. Recently, some clinical literature has suggested that patients with chronic obstructive pulmonary disease who are hypercapnic are unable to develop the same inspiratory pressures as equally obstructed eucapnic patients. Furthermore, a recent study in normal human subjects showed that artificially induced hypercapnia not only decreased the transdiaphragmatic pressure generated for a given electrical input, but also disposed the subjects to diaphragmatic fatigue more readily. We have demonstrated these same phenomena in the in vivo dog diaphragm and in the in vitro rat diaphragm. The overall hypothesis of this proposal is that acute and long term extracellular acidosis provokes mechanical dysfunction in the in vitro rat diaphragm by one or more of the following mechanisms: inhibiting the ability of cellular cation (Na-H) and anion (HCO3-C1) pumps to regulate intracellular pH; depleting high energy phosphates by inhibiting glycolytic or aerobic enzymes; modulating sarcolemmal or organellar calcium transport or altering intracellular calcium binding sites; provoking a depolarization of the resting membrane potential; changing the pattern of acetylcholine release at the neuromuscular junction of the diaphragm. Some of these mechanisms may be responsible acutely while others become so after a period of time. The proposal describes four sets of experiments which will test these mechanisms. Experiments using 31 phosphorus nuclear magnetic resonance will test hypotheses involving the effectos of acidosis on diaphragmatic intracellular pH and content of high energy phosphates. Experiments employing methods based on the use of 14C and 3H labelled glucoses will investigate the effects of acidosis on glycolytic and aerobic metabolism. Complete kinetic analysis of 45 calcium efflux data will permit quantitation of cellular calcium transport processes as well as changes in these processes caused by acidosis. Finally standard electrophysiological techniques will be used for the recording of resting membrane potentials and miniature end plate potentials.