Heemskerk J W, Farndale R W, Sage S O
Department of Human Biology and Biochemistry, University of Limburg, Maastricht, The Netherlands.
Biochim Biophys Acta. 1997 Jan 10;1355(1):81-8. doi: 10.1016/s0167-4889(96)00113-9.
We have investigated the actions of the PLC inhibitor, U73122, and its close analogue, U73343, which does not inhibit PLC, in Fura-2-loaded human platelets. Rises in [Ca2+]i evoked by thrombin and collagen, and the TxA2-dependent rise in [Ca2+]i evoked by thapsigargin, were abolished by U73122, indicating that it inhibits the activity of both beta and gamma isoforms of PLC. The supposed control compound U73343, was found to inhibit TxA2 formation; it therefore partially inhibited the rise in [Ca2+]i evoked by low concentrations of thrombin, by thapsigargin or by collagen. U73343 had a greater effect than aspirin on the action of collagen, indicating an action on the TxA2-independent component of the signal, via PLC gamma-U73343 lowered TxA2 production by inhibiting the activation of cPLA2, probably at a tyrosine phosphorylation step. U73343 seems to inhibit only the tyrosine kinases involved in the activation of PLC gamma and the generation of TxA2. In contrast, U73122 increased tyrosine phosphorylation of platelet proteins, perhaps by inhibiting receptor independent tyrosine phosphatases, but inhibited all further tyrosine phosphorylation on addition of thrombin or other agonists.
我们研究了磷脂酶C（PLC）抑制剂U73122及其不抑制PLC的类似物U73343对负载Fura-2的人血小板的作用。凝血酶和胶原引发的细胞内钙离子浓度（[Ca2+]i）升高，以及毒胡萝卜素引发的依赖血栓素A2（TxA2）的[Ca2+]i升高，均被U73122消除，这表明它抑制了PLC的β和γ亚型的活性。人们发现，所谓的对照化合物U73343可抑制TxA2的形成；因此，它部分抑制了低浓度凝血酶、毒胡萝卜素或胶原引发的[Ca2+]i升高。U73343对胶原作用的影响比阿司匹林更大，这表明它通过PLCγ作用于信号的不依赖TxA2的成分——U73343可能在酪氨酸磷酸化步骤通过抑制胞质磷脂酶A2（cPLA2）的激活来降低TxA2的产生。U73343似乎仅抑制参与PLCγ激活和TxA2生成的酪氨酸激酶。相比之下，U73122可能通过抑制非受体依赖性酪氨酸磷酸酶增加血小板蛋白的酪氨酸磷酸化，但在加入凝血酶或其他激动剂后抑制所有进一步的酪氨酸磷酸化。
