Abdel-Latif A A, Zhang Y, Yousufzai S Y
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta 30912-2100.
Curr Eye Res. 1991 Mar;10(3):259-65. doi: 10.3109/02713689109003448.
We have investigated the effects of endothelin-1 (ET1) on phospholipid hydrolysis and 3H-arachidonic acid (AA) release and prostaglandin synthesis in the rabbit iris sphincter smooth muscle. ET1 actions are concentration- and time dependent with an EC50 for AA release of 1 nM and t1/2 value of 1.5 min. We have identified the AA metabolites released by ET1, employing HPLC, as both cyclooxygenase and lipoxygenase products. The AA released by ET1 appears to derive mainly from the phosphoinositides through phospholipase A2, rather than phospholipase C activation. A key role for phospholipase A2 in AA release in the sphincter muscle is supported by the following observations. (1) Pretreatment of the labeled sphincter with the phorbol ester, PDBu (100 nM) inhibited ET1-stimulated IP3 formation, but it potentiated ET1-stimulated AA release. (2) Pretreatment of the labeled tissue with isoproterenol (5 M) inhibited ET1-stimulated IP3 production without altering AA release. (3) The potency for ET1-stimulated AA release (EC50 = 1 nM) was much higher than that for IP3 formation (EC50 = 45 nM). (4) There were considerable increases, rather than decreases, in 1, 2-diacyl-glycerol formation (1.2-folds) and its phosphorylated product, phosphatidic acid (2.6-folds) by ET1. It is concluded that in the rabbit iris sphincter ET1 is a potent agonist for AA release and eicosanoid synthesis and that AA is released from phosphoinositides mainly through activation of phospholipase A2.
我们研究了内皮素 -1（ET1）对兔虹膜括约肌平滑肌中磷脂水解、3H - 花生四烯酸（AA）释放以及前列腺素合成的影响。ET1的作用具有浓度和时间依赖性，AA释放的EC50为1 nM，t1/2值为1.5分钟。我们采用高效液相色谱法（HPLC）鉴定了ET1释放的AA代谢产物，它们是环氧化酶和脂氧合酶的产物。ET1释放的AA似乎主要通过磷脂酶A2从磷酸肌醇中释放出来，而不是通过磷脂酶C的激活。以下观察结果支持了磷脂酶A2在括约肌肌肉AA释放中的关键作用。（1）用佛波酯PDBu（100 nM）预处理标记的括约肌可抑制ET1刺激的IP3形成，但增强了ET1刺激的AA释放。（2）用异丙肾上腺素（5 μM）预处理标记组织可抑制ET1刺激的IP3产生，而不改变AA释放。（3）ET1刺激AA释放的效力（EC50 = 1 nM）远高于刺激IP3形成的效力（EC50 = 45 nM）。（4）ET1使1,2 - 二酰甘油的形成增加了1.2倍，其磷酸化产物磷脂酸增加了2.6倍，呈显著增加而非减少。结论是，在兔虹膜括约肌中，ET1是AA释放和类花生酸合成的有效激动剂，且AA主要通过磷脂酶A2的激活从磷酸肌醇中释放出来。
