Mode of Action of Oxygen Free Radicals in Excitation-Contraction Coupling System of Masseter Muscle

在本研究计划中，我们希望利用离体肌浆网（SR）、肌原纤维、肌细胞膜和肌细胞膜研究1）Ca ^<2+>动力学，2）Ca ^<2 +>渗透途径的特征，3）钙调蛋白在Ca^<2+>流行为中的作用，4）酸中毒对兴奋-收缩偶联系统的影响，5）自由氧自由基的作用，或犬咬肌的未分级匀浆。咬肌SR释放Ca^2+的能力强于股肌和心肌SR。被动的Ca^2+流出不是载体介导的，也不是兴奋-收缩偶联过程中Ca^2+释放的可能途径.为了观察到大量的被动Ca^2+流出，可能需要一定的最小Ca^2+梯度。这一系列的研究假设，在SR囊泡中Ca^<2+>积累过程中的被动外排途径相对较小.钙调素依赖性过程通过调节SR膜上的Ca^2+释放通道，在ATP水解和Ca^2+积累的偶联中发挥功能性作用.酸中毒使肌浆网中的Ca^2+转运与ATP水解显著分离，并显著改变肌原纤维ATP酶活性。据推测，这些缺陷可以解释在缺血期间观察到的骨骼肌细胞功能的抑制。咬肌的损伤是由于唾液腺素合成增加而产生的自由基超氧阴离子以及在低pH下由超氧阴离子转化为更致命的羟基自由基而引起的。酸中毒可通过氧自由基机制抑制咬肌匀浆中SR Ca^2+转运。

In this research project, we wished to investigate 1) Ca^<2+> kinetics, to characterize 2) the route of Ca^<2+> permeability, to define 3) the role of calmodulin in Ca^<2+> fluxes behavior, and to detrmine 4) the effect of acidosis on the excitation-contraction coupling system and 5) the effect of free oxygen radicals using isolated sarcoplasmic reticulum (SR), myofibrils, or the unfractionated homogenate of canine masseter muscle.1. The SR from masseter muscle has greater capability of Ca^<2+> release than that from femoral muscle or heart muscle. The passive Ca^<2+> efflux is not carrier mediated, and is not a likely route of Ca^<2+> release during excitation-contraction coupling.2. Some minimal Ca^<2+> gradient may be required in order to observe a substantial passive Ca^<2+> efflux. It is postulated in this series of research that passive route of efflux during Ca^<2+> accumulation in the SR vesicles is relatively small.3. Calmodulin-dependent process plays a functional role in the coupling of ATP hydrolysis and Ca^<2+> accumulation through regulation of Ca^<2+> release channels in the SR membrane.4. Acidosis significantly uncouples Ca^<2+> transport from ATP hydrolysis in the SR and significantly alters myofibrillar ATPase activity. It is hypothesized that these defects may explain an observed depression in skeletal muscle cell function during ischemia.5. Damage to the masseter muscle is caused by a free radical superoxide anion generated as a result of increased prostaglandins synthesis, and by the production of more lethal hydroxyl radical switched from the production of superoxide anion at low pH.Acidosis can depress SR Ca^<2+> transport in the homogenate of masseter muscle by an oxygen free radical mechanism.