Nakahata N, Matsuoka I, Ono T, Nakanishi H
Department of Pharmacology, Fukushima Medical College, Japan.
Eur J Pharmacol. 1989 Mar 29;162(3):407-17. doi: 10.1016/0014-2999(89)90331-2.
The properties of thromboxane A2 (TXA2) receptors were examined in 1321N1 human astrocytoma cells. 9,11-Epithio-11,12-methanothromboxane A2 (STA2), a stable analogue of TXA2, stimulated the accumulation of inositol phosphates (IPs) with an EC50 of about 50 nM. The STA2-induced accumulation of IPs was inhibited concentration dependently by ONO3708, a TXA2 receptor antagonist, with an inhibition constant (Ki) of about 10 nM. Inositol trisphosphate (IP3) was accumulated more rapidly than inositol bisphosphate (IP2) in response to STA2. HPLC analysis indicated that inositol 1,4,5-trisphosphate accumulated in the presence of STA2. STA2 alone had no effect on the accumulation of IPs in membrane preparations but it potentiated the accumulation induced by GTP gamma S. [3H]SQ29548, a TXA2 receptor antagonist, bound specifically to TXA2 receptors, expressing a single binding site with a dissociation constant (Kd) of 10.9 nM. The competition curve for STA2 inhibition of [3H]SQ29548 binding was shifted to the right and was steeper in the presence of GTP gamma S. Pertussis toxin (IAP) elicited ADP-ribosylation of 41KD protein but had no effect on the sensitivity to GTP of the STA2 inhibition of SQ29548 binding or of STA2-induced accumulation of IPs. It is concluded from these results that the stimulation of TXA2 receptors results in activation of phospholipase C via a GTP binding protein and that the protein is not a substrate for IAP.
在1321N1人星形细胞瘤细胞中检测了血栓素A2（TXA2）受体的特性。9,11-环氧-11,12-甲撑血栓素A2（STA2）是TXA2的稳定类似物，它刺激肌醇磷酸（IPs）的积累，其半数有效浓度（EC50）约为50 nM。TXA2受体拮抗剂ONO3708浓度依赖性地抑制STA2诱导的IPs积累，抑制常数（Ki）约为10 nM。响应STA2时，肌醇三磷酸（IP3）的积累比肌醇二磷酸（IP2）更快。高效液相色谱分析表明，在STA2存在下积累了肌醇1,4,5-三磷酸。单独的STA2对膜制剂中IPs的积累没有影响，但它增强了由GTPγS诱导的积累。TXA2受体拮抗剂[3H]SQ29548特异性结合TXA2受体，表现出单一结合位点，解离常数（Kd）为10.9 nM。在GTPγS存在下，STA2抑制[3H]SQ29548结合的竞争曲线向右移动且更陡峭。百日咳毒素（IAP）引起41KD蛋白的ADP核糖基化，但对STA2抑制SQ29548结合或STA2诱导的IPs积累的GTP敏感性没有影响。从这些结果得出结论，TXA2受体的刺激通过GTP结合蛋白导致磷脂酶C的激活，并且该蛋白不是IAP的底物。
