ENZYME REGULATION IN MYOCARDIAL ADENOSINE PRODUCTION DURING ISCHEMIA & HYPOXIA

阐明AMP-腺苷代谢的生理作用 细胞周期及AMP与腺苷的关系 豚鼠离体心的形成、供氧不同 (95-10%O2)。净腺苷形成率(AMP-腺苷)和 测定冠状静脉流出物腺苷释放率；游离 胞内AMP用31P核磁共振仪测定。从95%O2切换到40%O2 胞浆游离时，游离AMP和腺苷形成增加4倍 腺苷和静脉腺苷的释放增加了15-20倍。在AMP中 在200~3000nmol/L范围内呈线性相关 游离AMP和腺苷形成；然而，腺苷释放增加 几倍于队形。而在95%的氧气中，只有6%的 形成的腺苷被释放，这一比例已经增加到22% 在40%氧气下，腺苷回收减少。选择性封锁 腺苷脱氨酶和激酶的活性表明通过 腺苷激酶在腺苷形成中所占比例从85%降至35% 缺氧。数学模型分析表明，这一明显 酶活性的下降不是由于饱和，而是由于 将腺苷激酶活性抑制到基础水平的6%。这个 数据显示a)腺苷的形成与AMP成正比 底物浓度和b)低氧降低腺苷激酶 活性；从而将心肌腺苷从抢救中分流出来 静脉释放的途径。总而言之，由于正常的高水平 低氧诱导的AMP-腺苷代谢循环的周转 抑制腺苷激酶导致小分子的扩增 游离AMP的变化主要是腺苷的上升。这一机制 在心脏的高敏感性中起着重要的作用 腺苷系统对氧合功能的损害。

To elucidate the physiological role of the AMP-adenosine metabolic cycle and to investigate the relation between AMP and adenosine formation, oxygen supply of isolated guinea pig hearts was varied (95-10% O2). Net adenosine formation rate (AMP - adenosine) and coronary venous effluent adenosine release rate were measured; free cytosolic AMP was determined by 31P NMR. Switching from 95 to 40% O2 increased free AMP and adenosine formation 4-fold while free cytosolic adenosine and venous adenosine release rose 15-20 fold. In the AMP range from 200 to 3000 nmol/L there was a linear correlation between free AMP and adenosine formation; however, adenosine release increased several-fold more than formation. While at 95% O2 only 6% of adenosine formed were released, this fraction increased to 22% already at 40% O2 demonstrating reduced adenosine salvage. Selective blockade of adenosine deaminase and kinase indicated that flux through adenosine kinase decreased from 85 to 35% of adenosine formation in hypoxia. Mathematical model analysis indicated that this apparent decrease in enzyme activity was not due to saturation but to the inhibition of adenosine kinase activity to 6% of basal levels. The data show a) that adenosine formation is proportional to the AMP substrate concentration and b) that hypoxia decreases adenosine kinase activity; thereby shunting myocardial adenosine from the salvage pathway to venous release. In conclusion, because of the normal high turnover of the AMP-adenosine metabolic cycle, hypoxia-induced inhibition of adenosine kinase causes the amplification of small changes in free AMP into a major rise in adenosine. This mechanism plays an important role in the high sensitivity of the cardiac adenosine system to impaired oxygenation.