Yano M, el-Hayek R, Ikemoto N
Boston Biomedical Research Institute, Massachusetts 02114, USA.
Biochemistry. 1995 Oct 3;34(39):12584-9. doi: 10.1021/bi00039a013.
Perchlorate is one of the most potent activators of skeletal muscle excitation-contraction (E-C) coupling reported in the literature, but the detailed mechanism of its action remains to be elucidated. In an attempt to further resolve the mode of perchlorate action, the effects of increasing concentrations of perchlorate on the voltage-dependent (T-tubule-mediated) and voltage-independent portions of Ca2+ release were investigated using the isolated triad model. Low concentrations of perchlorate (< or = 10 mM) activated SR Ca2+ release only when the T-tubule moiety was chemically depolarized. Higher concentrations of perchlorate (30-100 mM), on the other hand, produced significant activation of SR Ca2+ release, regardless of whether or not the T-tubule was depolarized. In order to gain further insights, we monitored the conformational change in the junctional foot protein (JFP), which presumably is an important intermediate step in E-C coupling [Yano, M., El-Hayek, R., & Ikemoto, N. (1995) J. Biol. Chem. 270, 3017-3021], using the fluorescently labeled triad preparation. Again, low concentrations of perchlorate (< or = 10 mM) produced a preferential activation of voltage-dependent protein conformational change, while higher concentrations of perchlorate produced significant activation of voltage-independent protein conformational change. An increase in the ryanodine binding by perchlorate occurred only in the higher concentration range where the voltage-independent protein conformational change was activated. These results suggest that perchlorate activates E-C coupling by acting on at least two different steps: at lower concentrations, on the T-tubule-to-JFP signal transmission step; at higher concentrations, on the JFP directly.
高氯酸盐是文献报道的最有效的骨骼肌兴奋-收缩（E-C）偶联激活剂之一，但其详细作用机制仍有待阐明。为了进一步解析高氯酸盐的作用模式，我们使用分离的三联体模型研究了不断增加浓度的高氯酸盐对电压依赖性（T小管介导）和电压非依赖性Ca2+释放部分的影响。低浓度的高氯酸盐（≤10 mM）仅在T小管部分发生化学去极化时才激活肌浆网Ca2+释放。另一方面，较高浓度的高氯酸盐（30 - 100 mM）则会显著激活肌浆网Ca2+释放，无论T小管是否去极化。为了深入了解，我们使用荧光标记的三联体制剂监测连接足蛋白（JFP）的构象变化，推测这可能是E-C偶联中的一个重要中间步骤[矢野，M.，埃尔-哈耶克，R.，& 池本，N.（1995年）《生物化学杂志》270，3017 - 3021]。同样，低浓度的高氯酸盐（≤10 mM）优先激活电压依赖性蛋白构象变化，而较高浓度的高氯酸盐则显著激活电压非依赖性蛋白构象变化。高氯酸盐引起的兰尼碱结合增加仅发生在激活电压非依赖性蛋白构象变化的较高浓度范围内。这些结果表明，高氯酸盐通过作用于至少两个不同步骤来激活E-C偶联：在较低浓度下，作用于T小管到JFP的信号传递步骤；在较高浓度下，直接作用于JFP。
