FUNCTIONAL CHANGES IN DIAPHRAGMATIC FATIGUE

在本申请中提出的实验的目的是提供一种 更清楚地了解细胞机制负责减少 由于酸中毒而产生的收缩力。 最近，一些临床文献表明， 高碳酸血症的阻塞性肺病患者不能发展成 与同等阻塞的正常碳酸血症患者相同的吸气压力。 此外，最近对正常人的一项研究表明， 人工诱导的高碳酸血症不仅降低了 对于给定的电输入产生的压力，但也布置成 更容易出现脑疲劳。 我们已经证明了这些 在体内狗横膈膜和体外大鼠中的现象相同 隔膜 这一建议的总体假设是， 细胞外酸中毒引起离体大鼠的机械功能障碍 通过以下机制中的一个或多个来控制隔膜： 细胞阳离子（Na-H）和阴离子（HCO 3-C1）泵调节 细胞内pH;通过抑制糖酵解消耗高能磷酸盐 或需氧酶;调节肌膜或细胞器钙转运 或改变细胞内钙结合位点;引起去极化 静息膜电位;改变乙酰胆碱的模式 在隔膜的神经肌肉接头处释放。 其中一些 机制可能是急性责任，而其他人成为一段时间后， 时间了 该提案描述了四组实验，将测试这些 机制等 使用31磷核磁共振的实验 将测试假设，包括酸中毒对糖尿病的影响， 细胞内pH和高能磷酸盐含量。 实验 采用基于使用14 C和3 H标记的葡萄糖的方法将 研究酸中毒对糖酵解和有氧代谢的影响。 对45个钙外排数据进行完整的动力学分析， 定量细胞钙转运过程以及 这些过程由酸中毒引起。 最后，标准电生理 技术将用于记录静息膜电位 和微型终板电位。

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.