Kawaguchi H, Shoki M, Iizuka K, Sano H, Sakata Y, Yasuda H
Department of Cardiovascular Medicine, Hokkaido University School of Medicine, Sapporo, Japan.
Biochim Biophys Acta. 1991 Sep 3;1094(2):161-7. doi: 10.1016/0167-4889(91)90004-h.
We observed that in hypoxic myocardial cells prostacyclin and arachidonic acid release increased and that during hypoxia phospholipid degradation also occurred. In order to clarify the mechanism of phospholipid degradation, we determined the activity of phospholipases A2 and C. We found that phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were markedly decreased and that lysophosphatidylcholine and lysophosphatidylethanolamine were increased. In contrast, there was only slight phosphatidylinositol degradation and no lysophosphatidylinositol elevation was observed. These results show that phospholipase A2 was activated in hypoxic myocytes and had substrate specificity towards PC and PE. To study phospholipase C activity, membrane phospholipids were labeled with [3H]choline, [3H]inositol or [3H]ethanolamine. The release of inositol was observed, but neither choline nor ethanolamine was released. In hypoxia, myocardial-cell phospholipase C has high substrate specificity towards phosphatidylinositol. The activation of phospholipases is closely related to the intracellular Ca2+ concentration; it is though that inositol polyphosphatides may regulate intracellular Ca2+. We determined how Ca2+ influx occurs in hypoxia. beta-Adrenergic blockade and Ca2+ antagonists markedly suppressed Ca2+ influx, phospholipase A2 activity, phospholipase C activity and cell death. However, the alpha 1-adrenergic blockade was less effective in suppressing these phenomena. These results suggest that in hypoxic myocardial cells Ca2+ influx mediated by beta-adrenergic stimulation activates phospholipases A2 and C, and that phospholipid degradation and prostacyclin release then occur.
我们观察到，在缺氧心肌细胞中，前列环素和花生四烯酸释放增加，并且在缺氧期间也发生了磷脂降解。为了阐明磷脂降解的机制，我们测定了磷脂酶A2和C的活性。我们发现磷脂酰胆碱（PC）和磷脂酰乙醇胺（PE）明显减少，而溶血磷脂酰胆碱和溶血磷脂酰乙醇胺增加。相比之下，磷脂酰肌醇只有轻微降解，未观察到溶血磷脂酰肌醇升高。这些结果表明，磷脂酶A2在缺氧心肌细胞中被激活，并且对PC和PE具有底物特异性。为了研究磷脂酶C的活性，用[3H]胆碱、[3H]肌醇或[3H]乙醇胺标记膜磷脂。观察到肌醇的释放，但胆碱和乙醇胺均未释放。在缺氧状态下，心肌细胞磷脂酶C对磷脂酰肌醇具有高底物特异性。磷脂酶的激活与细胞内Ca2+浓度密切相关；据认为肌醇多磷酸可能调节细胞内Ca2+。我们确定了缺氧时Ca2+内流是如何发生的。β-肾上腺素能阻断剂和Ca2+拮抗剂显著抑制Ca2+内流、磷脂酶A2活性、磷脂酶C活性和细胞死亡。然而，α1-肾上腺素能阻断在抑制这些现象方面效果较差。这些结果表明，在缺氧心肌细胞中，由β-肾上腺素能刺激介导的Ca2+内流激活磷脂酶A2和C，然后发生磷脂降解和前列环素释放。
