The pathophysiological significanse and mechanism of activation of key enzyme responsible for adenosine production in ischemic preconditioning.

我们已经报道了化学预适应（IP）中的心脏保护作用可归因于外5′-核苷酸酶（ecto-5′nt）的激活，外5′-核苷酸酶是犬心肌中负责腺苷产生的关键酶，并且外5′- nt被蛋白激酶C （PKC）激活。在开胸犬中，通过4次5分钟的冠状动脉闭塞产生IP，间隔5分钟。心肌外泌素-5′nt活性和腺苷释放增加，但外泌素-5′nt抑制剂（AMP-CP）使两者钝化。AMP-CP对梗死面积的限制作用也减弱。此外，短暂给予甲氧沙明（α 1-肾上腺素受体的刺激剂）和PMA （PKC的激活剂）4次，每次5分钟，间隔5分钟，模拟了IP后ecto-5'NT活性的增加和梗死面积的限制作用。接下来，我们验证了缺血预适应（IP）归因于α - pkc激活的假设。IP激活Ca^<2+>-依赖的PKC。免疫印迹（IB）显示，与对照心肌相比，α - pkc含量增加，但β -、δ -和epsilon-PKC含量不变。在相同的膜组分中，ecto-5'NT活性增加。然后，我们检测了PKC是否在犬预处理心肌中磷酸化外5′T。免疫沉淀的ecto-5'NT为IB，有抗磷酸化抗体。我们观察到免疫沉淀的ecto-5'NT的丝氨酸-茶氨酸磷酸化。此外，PKC和ecto-5'NT因IP而增加的活性被减弱，免疫沉淀的ecto-5'NT的丝氨酸-苏氨酸磷酸化未被GY109203X（蛋白激酶C的特异性抑制剂）检测到。我们得出结论，心肌中的ecto-5'NT被PKC磷酸化并激活，以增加腺苷的释放。体外5′nt磷酸化激活是心肌梗死的重要机制。少

We have reported that cardioprotection in is chemic preconditining (IP) is attributable to activation of ecto-5'-nucleotidase (ecto-5'NT), akey enzyme responsible for adenosine production in the canine myocadium, and that ecto-5'NT is activated by protein kinase C (PKC). In the open chest dogs, IP was produced by 4 times of 5-min coronary occlusion with a 5-min interval. Myocardial ecto-5'NT activity and adenosine release were increased after IP,but both were blunted by an inhibitor of ecto-5'NT (AMP-CP). The infarct size-limiting effect was also blunted by AMP-CP.Futhermore, transient administration (4 times of 5-min coronary infusion with a 5-min interval) of methoxamine (an stimulator of alpha 1-adrenoceptor) and PMA (an activator of PKC) mimicked the increase in ecto-5'NT activity and the infarct size-limiting effect after IP.Next, we tested the hypothesis that ischemic preconditining (IP) is attributable to activation of alpha-PKC.IP activated Ca^<2+>-dependent PKC of the membrane … More faction. Immunoblotting (IB) of the membrane fraction revealed the increases in the contents of alpha-PKC without changing the contents of beta-, delta-, and epsilon-PKC compared with the control myocardium. In the same membrane fractions, ecto-5'NT activity increased. And then, we examined whether PKC phospholylates ecto-5' T in the canine preconditioned myocardium. Immunoprecipitated ecto-5'NT was IB with antiphosphorylation antibodies. We observed the serine-theonine phosphorylation of immunoprecipitated ecto-5'NT due to the IP procedure. Futhermore, the increases in the activities of PKC and ecto-5'NT due to IP were blunted and the serine-threonine phosphorylation of immunoprecipitated ecto-5'NT was not detected by GY109203X (a specific inhibitor of protein kinase C). We conclude that ecto-5'NT in the myocardium is phosphorylated and activated by PKC in the IP to increase the adenosine relase. Activation of ecto-5'NT by phosphorylation is an important mechanism for cadioprotection in IP. Less