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

在这个研究项目中，我们希望研究1)Ca^<2+>动力学，表征2)Ca^<2+>渗透性的途径，定义3)钙调素在Ca^<2+>通量行为中的作用，确定4)酸中毒对兴奋-收缩耦合系统的影响，5)自由基的影响，使用分离的肌浆网（SR），肌原纤维，或未分离的犬咬肌匀浆。咬肌SR释放Ca^<2+>的能力高于股肌和心肌。Ca^<2+>的被动外排不是载体介导的，也不是兴奋-收缩耦合过程中Ca^<2+>释放的可能途径。为了观察到大量的被动Ca^<2+>外流，可能需要一些最小的Ca^<2+>梯度。本系列研究推测，Ca^<2+>在SR囊泡积累过程中的被动外排途径相对较小。钙调素依赖过程通过调节SR膜内Ca^<2+>释放通道，在ATP水解和Ca^<2+>积累的偶联中发挥功能作用。酸中毒使SR中ATP水解中的Ca^<2+>转运偶联，并显著改变肌纤维ATP酶活性。据推测，这些缺陷可能解释了在缺血期间观察到的骨骼肌细胞功能下降。咬肌的损伤是由于前列腺素合成增加而产生的自由基超氧阴离子和低ph下超氧阴离子产生的更致命的羟基自由基的产生引起的，酸中毒可以通过氧自由基机制抑制咬肌均质液中SR Ca^<2+>的运输。

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.