Moores T S, Hasdemir B, Vega-Riveroll L, Deuchars J, Parson S H
School of Biomedical Sciences, Worsley Building, University of Leeds, LS2 9JT Leeds, UK.
Brain Res. 2005 Feb 9;1034(1-2):40-50. doi: 10.1016/j.brainres.2004.12.001.
Adenosine triphosphate is released into the synaptic cleft of the neuromuscular junction during normal synaptic transmission, and in much greater quantities following injury and ischaemia. There is much data to suggest roles for presynaptic P2 receptors but little to demonstrate which specific receptor subunits are present. Here we show P2X7 receptor subunits on presynaptic motor nerve terminals from birth, but no evidence for P2X1, P2X2, P2X3, P2X4, P2X5 or P2X6 receptor subunits. Further, P2X receptor subunits are present as multimeric, membrane-inserted receptors. A selective agonist, 2'-3'-O-(4-benzoylbenzoyl)-adenosine 5'-triphosphate (BzATP: 100 microM), triggers vesicle release from motor nerve terminals, which is blocked by P2X7RS-specific concentrations of periodate oxidised ATP (OxATP: 100 microM) and brilliant blue G (BBG: 1 microM), but not by suramin (100 microM). Vesicle release is enhanced in the absence of extracellular divalent cations and occurs through activation of the ion channel and not any associated large pore, as we failed to label nerve terminals with large membrane-impermeant molecules after addition of BzATP. We conclude that a P2X7-like receptor is present at mouse motor nerve terminals, and that their activation promotes vesicle release.
在正常突触传递过程中，三磷酸腺苷会释放到神经肌肉接头的突触间隙中，而在损伤和缺血后释放量会大幅增加。有大量数据表明突触前P2受体发挥了作用，但几乎没有证据表明存在哪些特定的受体亚基。在此我们发现，从出生起突触前运动神经末梢就存在P2X7受体亚基，但没有证据表明存在P2X1、P2X2、P2X3、P2X4、P2X5或P2X6受体亚基。此外，P2X受体亚基以多聚体形式存在，且插入细胞膜。一种选择性激动剂，2'-3'-O-(4-苯甲酰苯甲酰)-腺苷5'-三磷酸（BzATP：100微摩尔），可触发运动神经末梢的囊泡释放，该释放被P2X7受体特异性浓度的高碘酸盐氧化ATP（OxATP：100微摩尔）和亮蓝G（BBG：1微摩尔）阻断，但不被苏拉明（100微摩尔）阻断。在没有细胞外二价阳离子的情况下，囊泡释放会增强，并且是通过离子通道的激活而非任何相关的大孔实现的，因为在添加BzATP后，我们未能用大的膜不透性分子标记神经末梢。我们得出结论，小鼠运动神经末梢存在一种类似P2X7的受体，其激活可促进囊泡释放。
