Characterization of presynaptic calcium channels with omega-conotoxin MVIIC and omega-grammotoxin SIA: role for a resistant calcium channel type in neurosecretion.
Characterization of presynaptic calcium channels with omega-conotoxin MVIIC and omega-grammotoxin SIA: role for a resistant calcium channel type in neurosecretion.
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发表时间：
1995-02
影响因子：
3.6
通讯作者：
T. Turner;R. A. Lampe;K. Dunlap
中科院分区：
文献类型：
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作者：
T. Turner;R. A. Lampe;K. Dunlap
本文研究了肽类Ca ~（2+）通道拮抗剂ω-芋螺毒素（omega-CTX）MVIIC和ω-格拉姆毒素（omega-GTX）SIA对大鼠脑突触体[~ 3 H]谷氨酸释放的影响。相对于ω-GTX SIA（3.6 x 10（5）M-1 sec-1），ω-CTX MVIIC（1.1 x 10（4）M-1 sec-1）的伪一级缔合常数较小。平衡实验表明，omega-CTX MVIIC阻断了30 mM KCl诱发的约70%的Ca（2+）依赖性谷氨酸释放（IC 50约为200 nM），而omega-GTX SIA几乎消除了释放，效力较低（IC 50约为700 nM）。在较强的去极化（60 mM KCl）下，两种毒素（1 μ M）均未显示出显著的释放阻断，但当这些或其他Ca 2+通道拮抗剂（ω-CTX GVIA或ω-蛇曲霉毒素IVA）组合使用时，大部分释放被阻断。对ω-CTX MVIIC具有抗性的[3 H]谷氨酸释放的特征在于其对ω-GTX SIA和无机阻滞剂Ni 2+阻滞的敏感性。ω-GTX SIA和Ni ~（2+）都是相对较弱的耐药释放阻滞剂。这些结果表明，以前未表征的Ca 2+通道存在于神经末梢中，并且可以根据其对ω-CTX MVIIC的抗性和其对ω-GTX SIA和Ni 2+的弱敏感性来区分。因此，至少有三种通道类型（P，N和“抗性”型）有助于神经末梢中的兴奋-分泌偶联。
The peptide Ca2+ channel antagonists omega-conotoxin (omega-CTX) MVIIC and omega-grammotoxin (omega-GTX) SIA were studied by measuring their effects on the release of [3H]glutamate from rat brain synaptosomes. The pseudo-first-order association constant for omega-CTX MVIIC (1.1 x 10(4) M-1 sec-1) was small, relative to that for omega-GTX SIA (3.6 x 10(5) M-1 sec-1). Equilibrium experiments showed that omega-CTX MVIIC blocked approximately 70% of Ca(2+)-dependent glutamate release evoked by 30 mM KCl (IC50 approximately 200 nM), whereas omega-GTX SIA virtually eliminated release, with lower potency (IC50 approximately 700 nM). At stronger depolarizations (60 mM KCl), neither toxin (at 1 microM) showed significant block of release, but when these or other Ca2+ channel antagonists (omega-CTX GVIA or omega-agatoxin IVA) were used in combination a substantial fraction of release was blocked. [3H]Glutamate release that was resistant to omega-CTX MVIIC was characterized with respect to its sensitivity to block by omega-GTX SIA and the inorganic blocker Ni2+. Both omega-GTX SIA and Ni2+ were relatively weak blockers of the resistant release. These results suggest that a previously uncharacterized Ca2+ channel exists in nerve terminals and can be distinguished on the basis of its resistance to omega-CTX MVIIC and its weak sensitivity to omega-GTX SIA and Ni2+. Thus, at least three channel types (P, N, and a "resistant" type) contribute to excitation-secretion coupling in nerve terminals.