Okabe E, Fujimaki R, Murayama M, Ito H
Department of Pharmacology, Kanagawa Dental College, Japan.
Jpn Circ J. 1989 Sep;53(9):1132-7. doi: 10.1253/jcj.53.1132.
It has been proposed that a major target organelles damaged by the ischemic process, probably by the oxygen free radicals generated, is the portion of the excitation-contraction coupling system that regulates Ca2+ delivery (the sarcoplasmic reticulum and sarcolemma) to the contractile proteins. We tested this hypothesis by studying the effect of in vitro generation of oxygen free radicals from xanthine-xanthine oxidase system or dihydroxyfumarate (DHF)/Fe3+-ADP system on Ca2+ flux behavior of canine cardiac sarcoplasmic reticulum (SR); sarcolemmal (Na+, K+)-ATPase and Na+-Ca2+ exchange activities; and myofibrillar (Ca2+, Mg2+)-ATPase activity. Generation of oxygen free radicals by xanthine oxidase acting on xanthine as a substrate increased the passive Ca2+ efflux and decreased intravesicular Ca2+ with no effect on active Ca2+ influx (Ca2+-ATPase) of SR vesicles. Similar exposure of sarcolemmal vesicles to xanthine plus xanthine oxidase stimulated Na+-Ca2+ exchange activity. When sarcolemmal vesicles were incubated with DHF plus Fe3+-ADP, (Na+, K+)-ATPase activity was decreased. It is postulated that the SR Ca2+ efflux pathways but not catalytic activity of the Ca2+ pump and sarcolemmal (Na+, K+)-ATPase involving Na+-Ca2+ exchange activity are altered by oxygen free radicals, and such changes may partly account for the occurrence of intracellular Ca2+ overload during the course of myocardial ischemia. Interestingly, oxygen free radicals from xanthine-xanthine oxidase system had no effect on myofibrillar pCa-ATPase curve. From this set of observations we would hypothesize that the SR and sarcolemma may be the principal target organelles of oxygen free radicals attack in the ischemic injury and not the contractile proteins per se.
有人提出，缺血过程中主要受损的靶细胞器，可能是由所产生的氧自由基导致的，是兴奋 - 收缩偶联系统中调节Ca2+输送（肌浆网和肌膜）至收缩蛋白的部分。我们通过研究黄嘌呤 - 黄嘌呤氧化酶系统或二羟基富马酸（DHF）/Fe3+-ADP系统体外产生氧自由基对犬心肌肌浆网（SR）的Ca2+通量行为、肌膜（Na+，K+）-ATP酶和Na+-Ca2+交换活性以及肌原纤维（Ca2+，Mg2+）-ATP酶活性的影响，来验证这一假设。以黄嘌呤为底物，黄嘌呤氧化酶产生氧自由基增加了SR囊泡的被动Ca2+外流并降低了囊泡内Ca2+，而对SR囊泡的主动Ca2+内流（Ca2+-ATP酶）无影响。将肌膜囊泡类似地暴露于黄嘌呤加黄嘌呤氧化酶刺激了Na+-Ca2+交换活性。当肌膜囊泡与DHF加Fe3+-ADP一起孵育时，（Na+，K+）-ATP酶活性降低。据推测，氧自由基改变了SR的Ca2+外流途径，但不影响Ca2+泵和涉及Na+-Ca2+交换活性的肌膜（Na+，K+）-ATP酶的催化活性，并且这种变化可能部分解释了心肌缺血过程中细胞内Ca2+过载的发生。有趣的是，来自黄嘌呤 - 黄嘌呤氧化酶系统的氧自由基对肌原纤维pCa-ATP酶曲线没有影响。从这一系列观察结果我们推测，SR和肌膜可能是缺血损伤中氧自由基攻击的主要靶细胞器，而不是收缩蛋白本身。
