Pharmacological studies on toxins from marine organism

Maitotoxin （MTX）是一种水溶性毒素，是从钩鞭毛虫甘比铁饼毒中分离出来的。我们首次报道了MTX激活心脏质膜上电压无关的Ca^<2+>通道。甲氨蝶呤引起家兔洗涤血小板聚集。细胞内Ca^<2+>浓度（[Ca^<2+>] i）也因MTX的存在而升高。在不含Ca^<2+>的溶液中，mtx诱导的血小板聚集和[Ca^<2+>] i升高完全被消除。这些结果表明，mtx诱导的血小板活化是由Ca^<2+>-内流增强引起的，可能是通过电压无关的Ca^<2+>通道。从一种共生海藻中分离得到Zooxanthellatoxin-A (ZT-A)，确定其结构为62元内酯。ZT-A在兔血小板中引起聚集，但在不含Ca^<2+>的溶液中不引起血小板聚集或升高[Ca^<2+>] i。吲哚美辛和SQ-29548抑制血小板聚集和[Ca^<2+>]升高，ZT-A的作用更明显。这些结果表明ZT-A引起血小板质膜Ca^<2+>-内流。由此导致的[Ca^<2+>] i的增加随后刺激血小板中TXA_2的二次释放。在血小板中，ZT-A在1mM Ca^<2+>存在下引起42kDa的浓度依赖性蛋白酪氨酸磷酸化。染料木黄酮抑制蛋白酪氨酸磷酸化。42kDa蛋白通过抗丝裂原活化蛋白激酶（mapk）抗体免疫沉淀鉴定为p42^<mapk>。ZT-A释放血栓素（TX） B_2，促进花生四烯酸的释放。吲哚美辛完全抑制zt - a诱导的TXB_2释放，部分抑制MARK激活。这些结果表明ZT-A可能在外部Ca^<2+>存在的情况下激活蛋白酪氨酸激酶。被激活的酪氨酸激酶随后激活MAPK。MAPK的激活反过来通过磷脂酶A_2释放花生四烯酸，导致血小板释放TXA_2。详细的药理研究表明，磷脂酶A_2的活化与一种蛋白酪氨酸激酶有关。少

Maitotoxin (MTX) is a water-soluble toxin isolated from the dinoflagellate Gambierdiscus toxicus. We reported for the first time that MTX activates voltage-independent Ca^<2+> channels on the cardiac plasma membrane. MTX caused aggregation of rabbit washed platelets. The cytosolic Ca^<2+> concentration ([Ca^<2+>] i) was also increased by the presence of MTX.The MTX-induced platelet aggregation and [Ca^<2+>] i-increase were totally abolished in a Ca^<2+>-free solution. These results suggest that the MTX-induced platelet activation is caused by an enhanced Ca^<2+>-influx presumably through voltage-independent Ca^<2+> channels.Zooxanthellatoxin-A (ZT-A) was isolated from a symbiotic marine alga, and the structure of ZT-A was determined to be a 62-membered lactone. ZT-A caused aggregation in rabbit platlets, but did not cause platelet aggregation or infcrease [Ca^<2+>] i in a Ca^<2+>-free solution. Indomethacin and SQ-29548 inhibited platelet aggregation and the increase in [Ca^<2+>] i ind … More uced by ZT-A.These results suggest that ZT-A elicited Ca^<2+>-influx from platelet plasma membranes. The resulting increase in [Ca^<2+>] i subsequently stimulates the secondary release of TXA_2 from platelets.In platlets ZT-A caused concentration-dependent protein tyrosine phosphorylation of 42kDa in the presence of 1mM Ca^<2+>. The protein tyrosine phosphorylation was inhibited by genistein. The 42kDa protein was identified as p42^<mapk> by immunoprecipitation with an anti-mitogen-activated protein kinase (MAPK) antibody. ZT-A released thromboxame (TX) B_2 and stimulated the liberation of arachidonic acid. ZT-A-induced TXB_2 release was completely inhibited by indomethacin, while the MARK activation was partially inhibited by it. These results suggest that ZT-A may activate a protein tyrosine kinase in the presence of external Ca^<2+>. The activated protein tyrosin kinase subsequently activates MAPK.The activation of MAPK in turn causes the liberation of arachidonic acid via phospholipase A_2, resulting in the release of TXA_2 from platelets. The detailed pharmacological studies suggest that the phospolipase A_2 activation is relevant to a protein tyrosine kinase. Less