Gan S D, Fan M M, He G P
Brain Res. 1986 Mar 26;369(1-2):75-82. doi: 10.1016/0006-8993(86)90514-7.
To verify whether microtubules are involved in the mechanism of axoplasmic transport in vivo, [3H]leucine was injected into ventral horns of rats, and 3 h later Ca2+ or other drugs injected into sciatic nerves. The injection of 50-200 mM Ca2+, raising intra-axoplasmic Ca2+ levels, blocked transport above the intraneural injecting site and decreased microtubular density. Conversely, injection of 10 mM EGTA lowering the intra-axoplasmic Ca2+ induced the same changes. By combining the injection of 50 mM colchicine with 25 mM Ca2+ or 5 mM EGTA, the effects were additive in that transport was weakened further or even blocked and microtubules disappeared. Therefore, microtubules seemed to be a mediator between the injected drug and the blockade of transport and Ca2+ to be a regulator of axoplasmic transport in vivo. Tubulin, a subunit of microtubules, contains SH groups and Cd2+ is a chelate of them. By injection of 50-100 mM Cd2+, transport was weakened or blocked. The sulfhydryl inhibitor, N-ethylmaleimide increased, but the sulfhydryl donor, dimercaptosuccinate, abolished the effect of Cd2+ on transport. N-ethylmaleimide also amplified the Cd2+ effect on decreasing SH group content of sciatic nerve homogenate. There were 8.7 SH groups per tubulin monomer isolated from rabbit brain. The SH groups of tubulin in vitro and microtubular density in vivo were decreased with the increase of Cd2+ concentration. All these results indicated that microtubules play a role in the mechanism of axoplasmic transport.
为了验证微管是否参与体内轴浆运输机制，将[³H]亮氨酸注入大鼠腹角，3小时后将Ca²⁺或其他药物注入坐骨神经。注射50 - 200 mM Ca²⁺以提高轴浆内Ca²⁺水平，可阻断神经内注射部位上方的运输并降低微管密度。相反，注射10 mM乙二醇双四乙酸（EGTA）降低轴浆内Ca²⁺也会引起相同变化。将50 mM秋水仙碱与25 mM Ca²⁺或5 mM EGTA联合注射，其作用是相加的，即运输进一步减弱甚至被阻断，微管消失。因此，微管似乎是注射药物与运输阻断之间的介质，而Ca²⁺是体内轴浆运输的调节因子。微管的亚基微管蛋白含有巯基，而Cd²⁺是它们的螯合剂。注射50 - 100 mM Cd²⁺会使运输减弱或阻断。巯基抑制剂N - 乙基马来酰亚胺增强了这种作用，但巯基供体二巯基丁二酸消除了Cd²⁺对运输的影响。N - 乙基马来酰亚胺还增强了Cd²⁺对降低坐骨神经匀浆巯基含量的作用。从兔脑分离的每个微管蛋白单体有8.7个巯基。随着Cd²⁺浓度增加，体外微管蛋白的巯基和体内微管密度降低。所有这些结果表明微管在轴浆运输机制中起作用。
