McDonough S I, Swartz K J, Mintz I M, Boland L M, Bean B P
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA.
J Neurosci. 1996 Apr 15;16(8):2612-23. doi: 10.1523/JNEUROSCI.16-08-02612.1996.
Inhibition of voltage-dependent calcium channels by omega-conotoxin MVIIC (omega-CTx-MVIIC) was studied in various types of rat neurons. When studied with 5 mM Ba2+ as charge carrier, omega-CTx-MVIIC block of N-type calcium channels in sympathetic neurons was potent, with half-block at 18 nM. Block of N-type channels had a rapid onset (tau approximately 1 sec at 1 microM omega-CTx-MVIIC) and quick reversibility (tau approximately 30 sec). The rate of block was proportional to toxin concentration, consistent with 1:1 binding of toxin to channels, with a rate constant (k on) of approximately 1 X 10(6) M-1. sec-1. Both potency and rate of block were reduced dramatically with increasing concentrations of extracellular Ba2+ omega-CTx-MVIIC also blocked P-type calcium channels in cerebellar Purkinje neurons, but both development and reversal of block were far slower than for N-type channels. The rate of block was proportional to toxin concentration, with k on -1.5 x 10(3) M-1. sec-1 at 5 mM Ba2+. From this value and an unblocking time constant of approximately 200 min, a dissociation constant of approximately 50 nM was estimated. Thus, block of P-type channels is potent but very slow. In hippocampal CA3 pyramidal neurons, omega-CTx-MVIIC blocked approximately 50% of the high-threshold calcium channel current; one component (approximately 20%) was blocked with the rapid kinetics expected for N-type channels, whereas the other component was blocked slowly. The component blocked slowly was reduced but not eliminated by preexposure to 200 nM or 1 microM omega-Aga-IVA.
在多种类型的大鼠神经元中研究了ω-芋螺毒素MVIIC（ω-CTx-MVIIC）对电压依赖性钙通道的抑制作用。当以5 mM Ba2+作为电荷载体进行研究时，ω-CTx-MVIIC对交感神经元中N型钙通道的阻断作用很强，半数阻断浓度为18 nM。N型通道的阻断起效迅速（在1 μM ω-CTx-MVIIC时τ约为1秒）且可逆性快（τ约为30秒）。阻断速率与毒素浓度成正比，这与毒素与通道的1:1结合一致，结合速率常数（kon）约为1×10(6) M-1·sec-1。随着细胞外Ba2+浓度的增加，阻断的效力和速率均显著降低。ω-CTx-MVIIC还可阻断小脑浦肯野神经元中的P型钙通道，但阻断的形成和逆转均比N型通道慢得多。阻断速率与毒素浓度成正比，在5 mM Ba2+时kon为-1.5×10(3) M-1·sec-1。根据该值和约200分钟的解阻断时间常数，估计解离常数约为50 nM。因此，P型通道的阻断作用很强但非常缓慢。在海马CA3锥体神经元中，ω-CTx-MVIIC阻断了约50%的高阈值钙通道电流；其中一个成分（约20%）以N型通道预期的快速动力学被阻断，而另一个成分被缓慢阻断。预先暴露于200 nM或1 μM ω-Aga-IVA可使缓慢被阻断的成分减少但未消除。
