Wang C T, Peters-Golden M, Loch-Caruso R
Department of Environmental Health Sciences, University of Michigan, Ann Arbor 48109, USA.
Life Sci. 2001 Dec 14;70(4):453-70. doi: 10.1016/s0024-3205(01)01426-6.
Arachidonic acid release is an important regulatory component of uterine contraction and parturition, and previous studies showed that lindane stimulates arachidonic acid release from myometrium. The present study partially characterized the enzyme activity responsible for lindane-induced arachidonic acid release in myometrial cells. Lindane released arachidonic acid from cultured rat myometrial cells in concentration- and time-dependent manners. This release was primarily from phosphatidylcholine and phosphatidylinositol, and was independent of intracellular and extracellular calcium. In cells prelabeled with [3H]arachidonic acid, 85% of radiolabel was recovered as free arachidonate and only 5% was recovered as eicosanoids. Pretreatment with the antioxidants Cu, Zn-superoxide dismutase, alpha-tocopherol or Trolox did not significantly modify lindane-induced arachidonic acid release. Pretreatment of cells with the phosphatidylcholine-specific phospholipase C inhibitor D609, phosphatidylinositol-specific phospholipase C inhibitor ET-18-OCH3, or an interrupter of the phospholipase D pathway (ethanol) did not suppress lindane-induced arachidonic acid release. Although these results are consistent with calcium-independent phospholipase A2 activation by lindane, the calcium-independent phospholipase A2 inhibitor bromoenol lactone failed to inhibit lindane-induced arachidonic acid release in myometrial cells, even though bromoenol lactone effectively blocked arachidonic acid release in neutrophils. These results suggest that myometrial cells express a novel, previously unidentified phospholipase that is arachidonate-specific, calcium-independent, insensitive to bromoenol lactone, insensitive to reactive oxygen species activation, shows substrate preference for phosphatidylcholine and phosphatidylinositol, and is stimulated by lindane. Moreover, the data show that the overwhelming majority of arachidonic acid released remains as arachidonate, but that lindane does not significantly inhibit metabolism of arachidonate to eicosanoids.
花生四烯酸的释放是子宫收缩和分娩的一个重要调节成分，先前的研究表明林丹可刺激子宫肌层释放花生四烯酸。本研究部分表征了负责林丹诱导子宫肌层细胞释放花生四烯酸的酶活性。林丹以浓度和时间依赖性方式从培养的大鼠子宫肌层细胞中释放花生四烯酸。这种释放主要来自磷脂酰胆碱和磷脂酰肌醇，且与细胞内和细胞外钙无关。在用[3H]花生四烯酸预标记的细胞中，85%的放射性标记物以游离花生四烯酸盐形式回收，只有5%以类花生酸形式回收。用抗氧化剂铜锌超氧化物歧化酶、α-生育酚或曲洛昔芬预处理并没有显著改变林丹诱导的花生四烯酸释放。用磷脂酰胆碱特异性磷脂酶C抑制剂D609、磷脂酰肌醇特异性磷脂酶C抑制剂ET-18-OCH3或磷脂酶D途径阻断剂（乙醇）预处理细胞并没有抑制林丹诱导的花生四烯酸释放。尽管这些结果与林丹激活不依赖钙的磷脂酶A2一致，但不依赖钙的磷脂酶A2抑制剂溴苯醇内酯未能抑制林丹诱导的子宫肌层细胞花生四烯酸释放，尽管溴苯醇内酯有效地阻断了中性粒细胞中的花生四烯酸释放。这些结果表明子宫肌层细胞表达一种新型的、以前未鉴定的磷脂酶，该酶对花生四烯酸具有特异性、不依赖钙、对溴苯醇内酯不敏感、对活性氧激活不敏感、对磷脂酰胆碱和磷脂酰肌醇表现出底物偏好，并受林丹刺激。此外，数据表明释放的绝大多数花生四烯酸仍以花生四烯酸盐形式存在，但林丹并没有显著抑制花生四烯酸向类花生酸的代谢。
