钙离子通道阻滞剂神经毒素对小鼠神经肌肉接头处递质释放和突触前电流的影响。

Effects of Ca2+ channel blocker neurotoxins on transmitter release and presynaptic currents at the mouse neuromuscular junction.

作者信息

Katz E, Protti D A, Ferro P A, Rosato Siri M D, Uchitel O D

机构信息

Instituto de Biología Celular, Facultad de Medicina, Universidad de Buenos Aires, Paraguay, Argentina.

出版信息

Br J Pharmacol. 1997 Aug;121(8):1531-40. doi: 10.1038/sj.bjp.0701290.

DOI:10.1038/sj.bjp.0701290

PMID:9283685

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC1564850/

Abstract

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, ICa and IK(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 microM) and omega-MVIID (3 microM) strongly reduced transmitter release (> 80-90% blockade) whereas the selective N-type channel blocker omega-CgTx (5 microM) was ineffective. 3. The process of release was much more sensitive to omega-MVIIC (IC50 = 39 nM) than to omega-MVIID (IC50 = 1.4 microM). After almost completely blocking transmitter release (quantal content approximately 0.3% of its control value) with 3 microM omega-MVIIC, elevating the external [Ca2+] from 2 to 10 mM induced an increase of approximately 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 Ca(2+)-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, ICa and IK(Ca), respectively, were highly sensitive to low concentrations (10-30 nM) of omega-AgaIVA. The ICa and the IK(Ca) were also strongly reduced by 1 microM 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.

摘要

评估了电压依赖性钙通道（VDCC）阻滞剂ω-阿加毒素IVA（ω-AgaIVA）、ω-芋螺毒素GVIA（ω-CgTx）、ω-芋螺毒素MVIIC（ω-MVIIC）和ω-芋螺毒素MVIID（ω-MVIID）对小鼠膈膜标本中递质释放的影响。还评估了ω-AgaIVA和ω-MVIIC分别对小鼠耳上肌标本中神经束膜钙电流和钙依赖性钾电流（ICa和IK(Ca)）的影响。2. P型和Q型VDCC阻滞剂ω-AgaIVA（100 nM）以及P型、Q型和N型通道阻滞剂ω-MVIIC（1 μM）和ω-MVIID（3 μM）强烈降低递质释放（>80 - 90%阻断），而选择性N型通道阻滞剂ω-CgTx（5 μM）无效。3. 释放过程对ω-MVIIC（IC50 = 39 nM）比ω-MVIID（IC50 = 1.4 μM）更敏感。用3 μM ω-MVIIC几乎完全阻断递质释放（量子含量约为其对照值的0.3%）后，将细胞外[Ca2+]从2 mM提高到10 mM可使终板电位（e.p.p.）的量子含量增加约20倍（从0.2±0.04增加到4.8±1.4）。4. 在低钙高镁培养基中（释放概率低，量子含量 = 2±0.1）神经诱发的递质释放对ω-AgaIVA的敏感性（IC50 = 16.8 nM）与在生理盐溶液中相同。此外，钾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℃下进行，ω-AgaIVA对递质释放的作用可通过毒素洗脱逆转。相反，即使在室温下洗脱毒素两小时后，ω-AgaIVA的作用仍持续存在。5. 钙和钙依赖性钾突触前电流，即ICa和IK(Ca)，分别对低浓度（10 - 30 nM）的ω-AgaIVA高度敏感。1 μM ω-MVIIC也能强烈降低ICa和IK(Ca)。这两种毒素作用最显著的差异在于ω-MVIIC达到最大效应所需的孵育时间长。6. 总之，这些结果提供了更多证据表明哺乳动物神经肌肉接头处的突触传递是由Ca2+通过P型和/或Q型钙通道内流介导的。