Sergeeva Marina, Strokin Mikhail, Wang Hong, Ubl Joachim J, Reiser Georg
Institut für Neurobiochemie, Medizinische Fakultät der Otto-von-Guericke-Universität Magdeburg, Germany.
J Neurochem. 2002 Sep;82(5):1252-61. doi: 10.1046/j.1471-4159.2002.01052.x.
Arachidonic (AA) and docosahexaenoic acid (DHA) are the major polyunsaturated fatty acids (PUFAs) in the brain. However, their influence on intracellular Ca2+ signalling is still widely unknown. In astrocytes, the amplitude of thrombin- induced Ca2+ response was time-dependently diminished by AA and DHA, or by the AA tetraynoic analogue ETYA, but not by eicosapentaenoic acid (EPA). Thrombin-elicited Ca2+ response was reduced (20-30%) by 1-min exposure to AA or DHA. Additionally, 1-min application of AA or DHA together with thrombin in Ca2+-free medium blocked Ca2+ influx, which followed after readdition of extracellular Ca2+. EPA and ETYA, however, were ineffective. Long-term treatment of astrocytes with AA and DHA, but not EPA reduced the amplitude of the thrombin-induced Ca2+ response by up to 80%. AA and DHA caused a comparable decrease in intracellular Ca2+ store content. Only DHA and AA, but not EPA or ETYA, caused liberation of endogenous AA by cytosolic phospholipase A2 (cPLA2). Therefore, we reasoned that the suppression of Ca2+ response to thrombin by AA and DHA could be due to release of endogenous AA. Possible participation of AA metabolites, however, was excluded by the finding that specific inhibitors of the different oxidative metabolic pathways of AA were not able to abrogate the inhibitory AA effect. In addition, thrombin evoked AA release via activation of cPLA2. From our data we propose a novel model of positive/negative-feed-back in which agonist-induced release of AA from membrane phospholipids promotes further AA release and then suppresses agonist-induced Ca2+ responses.
花生四烯酸（AA）和二十二碳六烯酸（DHA）是大脑中主要的多不饱和脂肪酸（PUFA）。然而，它们对细胞内Ca2+信号传导的影响仍鲜为人知。在星形胶质细胞中，凝血酶诱导的Ca2+反应幅度随时间被AA、DHA或AA四炔类似物ETYA减弱，但不被二十碳五烯酸（EPA）减弱。凝血酶引发的Ca2+反应在暴露于AA或DHA 1分钟后降低（20 - 30%）。此外，在无Ca2+培养基中1分钟内同时应用AA或DHA与凝血酶可阻断Ca2+内流，在重新添加细胞外Ca2+后Ca2+内流随之发生。然而，EPA和ETYA无效。用AA和DHA而非EPA长期处理星形胶质细胞可使凝血酶诱导的Ca2+反应幅度降低高达80%。AA和DHA导致细胞内Ca2+储存含量出现类似程度的下降。只有DHA和AA而非EPA或ETYA可通过胞质磷脂酶A2（cPLA2）引起内源性AA的释放。因此，我们推断AA和DHA对凝血酶Ca2+反应的抑制可能是由于内源性AA的释放。然而，AA代谢产物的可能参与被以下发现排除：AA不同氧化代谢途径的特异性抑制剂无法消除AA的抑制作用。此外，凝血酶通过激活cPLA2诱发AA释放。根据我们的数据，我们提出了一个正/负反馈的新模型，其中激动剂诱导的膜磷脂中AA释放促进进一步的AA释放，进而抑制激动剂诱导的Ca2+反应。
