Effects of Ca2+ channel blocker neurotoxins on transmitter release and presynaptic currents at the mouse neuromuscular junction
Effects of Ca2+ channel blocker neurotoxins on transmitter release and presynaptic currents at the mouse neuromuscular junction
复制标题
DOI：
10.1038/sj.bjp.0701290
复制
发表时间：
1997-08-01
影响因子：
7.3
通讯作者：
Uchitel, OD
中科院分区：
文献类型：
--
作者：
Katz, E;Protti, DA;Uchitel, OD
1观察电压依赖性钙通道阻断剂omega-agatoxin IVA(omega-agatoxin IVA)、omega-conooxoxgGVIA(omega-CgTx)、omega-conooxoxinMVIIC(omega-MVIIC)和omega-conooxoxinMVIID(omega-MVIID)对小鼠膈肌神经递质释放的影响。我们还观察了omega-AgaIVA和omega-MVIIC对小鼠提肌耳廓准备过程中神经膜钙电流和钙依赖钾电流的影响。3释放过程对omega-MVIIC(IC50=39 nM)比对omega-MVIID(IC50=1.4mM)敏感得多。在用3亩M omega-MVIIC几乎完全阻断递质释放(量子含量接近其控制值的0.3%)后，将外部[Ca~(2+)]从2 mM提高到10 mM，终板电位的量子含量(E.P.P.)增加了近20倍。4低钙高镁介质(低释放率，量子含量=2+/-0.1)对omega-AgaIVA的敏感性与生理盐水相同(IC50=16.8 nM)。此外，K+诱发的递质释放对该毒素的作用也高度敏感(IC50=11.5 nM；100 nM>；95%阻断)。如果实验在31-33℃进行，omega-AgaIVA对递质释放的作用可以被毒素清洗逆转。相反，即使在室温下毒素清洗两小时后，omega-AgaIVA的作用仍然存在。5钙和钙依赖的钾突触前电流I-Ca和I-K(Ca)对低浓度(10-30 nM)的omega-AgaIVA高度敏感。1亩M omega-MVIIC还显著降低了I-Ca和I-K(Ca)。这两种毒素作用之间最显著的差异是与omega-MVIIC达到最大效果所需的较长孵化时间。6综上所述，这些结果提供了更多证据，表明哺乳动物神经肌肉接头的突触传递是通过P-和/或Q-型钙通道的钙离子进入而介导的。
1 The effects of the voltage-dependent calcium channel (VDCC) blockers omega-agatoxin IVA (omega-AgaIVA), omega-conotoxin GVIA (omega-CgTx), omega-conotoxin MVIIC (omega-MVIIC) and omega-conotoxin MVIID (omega-MVIID) were evaluated on transmitter release in the mouse diaphragm preparation. The effects of omega-AgaIVA and omega-MVIIC were also evaluated on the perineurial calcium and calcium-dependent potassium currents, I-Ca and I-K(Ca), respectively, in the mouse levator auris preparation.2 The P- and Q-type VDCC blocker omega-AgaIVA (100 nM) and P-Q-and N-type channel blockers omega-MVIIC (1 mu M) and omega-MVIID (3 mu M) strongly reduced transmitter release (> 80-90% blockade) whereas the selective N-type channel blocker omega-CgTx (5 mu M) was ineffective.3 The process of release was much more sensitive to omega-MVIIC (IC50=39 nM) than to omega-MVIID (IC50=1.4 mu M). After almost completely blocking transmitter release (quantal content similar to 0.3% of its control value) with 3 mu M omega-MVIIC, elevating the external [Ca2+] from 2 to 10 mM induced an increase of similar to 20 fold on the quantal content of the endplate potential (e.p.p.) (from 0.2+/-0.04 to 4.8+/-1.4).4 Nerve-evoked transmitter release in a low Ca2+-high Mg2+ medium (low release probability, quantal content = 2+/-0.1) had the same sensitivity to omega-AgaIVA (IC50=16.8 nM) as that in normal saline solutions. In addition, K+-evoked transmitter release was also highly sensitive to the action of this toxin (IC50=11.5 nM; 100 nM >95% blockade). The action of omega-AgaIVA on transmitter release could be reversed by toxin washout if the experiments were carried out at 31-33 degrees C. Conversely, the effect of omega-AgaIVA persisted even after two hours of toxin washout at room temperature.5 Both the calcium and calcium-dependent potassium presynaptic currents, I-Ca and I-K(Ca), respectively, were highly sensitive to low concentrations (10-30 nM) of omega-AgaIVA. The I-Ca and the I-K(Ca) were also strongly reduced by 1 mu M omega-MVIIC. The most marked difference between the action of these two toxins was the long incubation times required to achieve maximal effects with omega-MVIIC.6 In summary these results provide more evidence that synaptic transmission at the mammalian neuromuscular junction is mediated by Ca2+ entry through P- and/or Q-type calcium channels.