Subunit-specific mechanisms and proton sensitivity of NMDA receptor channel block
Subunit-specific mechanisms and proton sensitivity of NMDA receptor channel block
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DOI：
10.1113/jphysiol.2006.124958
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发表时间：
2007-05-15
影响因子：
5.5
通讯作者：
Traynelis, Stephen F.
中科院分区：
文献类型：
--
作者：
Dravid, Shashank M.;Erreger, Kevin;Traynelis, Stephen F.
我们比较了结构不同的通道阻滞剂对重组 NR1/NR2A、NRI/NR2B、NR1/NR2C 和 NR1/NR2D 受体的效力。 IC50 值随立体化学和亚基组成而变化，表明设计亚基选择性通道阻断剂是可能的。对于地佐西平 (MK-801)，在重组 NMDA 受体上测定的 MK-801 立体异构体的差异效力在体外和体内天然受体上得到了证实。由于质子传感器在结构和功能上都与通道门控紧密相连，因此我们研究了在通道孔中与门控机制相互作用的阻断分子是否可以差异化地感知受体的质子化。能够在激动剂解离过程中保留在孔中的阻滞剂表现出对细胞外 pH 值的最强依赖性，在促进通道关闭的酸性 pH 值下显得更有效。通道阻滞剂的 pK(α) 值的测定表明，氯胺酮的电离（而非其他阻滞剂）可以影响其 pH 依赖性效力。动力学模型和单通道研究表明，(-)MK-801 对 NR1/NR2A 的 pH 依赖性阻断反映了 MK-801 结合率的增加，而 (-)MK-801 则不然，尽管质子降低了通道开放概率，从而降低了 MK-801 对其结合位点的访问。改变 pH 敏感性的变构调节剂会改变 MK-801 的效力，支持这样的解释：MK-801 结合的 pH 敏感性反映了质子传感器的变化，而不是 pH 的二次影响。这些数据表明质子传感器和离子通道门之间的紧密耦合以及通道阻断的独特的亚基特异性机制。
We have compared the potencies of structurally distinct channel blockers at recombinant NR1/NR2A, NRI/NR2B, NR1/NR2C and NR1/NR2D receptors. The IC50 values varied with stereochemistry and subunit composition, suggesting that it may be possible to design subunit-selective channel blockers. For dizocilpine (MK-801), the differential potency of MK-801 stereoisomers determined at recombinant NMDA receptors was confirmed at native receptors in vitro and in vivo. Since the proton sensor is tightly linked both structurally and functionally to channel gating, we examined whether blocking molecules that interact in the channel pore with the gating machinery can differentially sense protonation of the receptor. Blockers capable of remaining trapped in the pore during agonist unbinding showed the strongest dependence on extracellular pH, appearing more potent at acidic pH values that promote channel closure. Determination of pK(alpha) values for channel blockers suggests that the ionization of ketamine but not of other blockers can influence its pH-dependent potency. Kinetic modelling and single channel studies suggest that the pH-dependent block of NR1/NR2A by (-)MK-801 but not (+)MK-801 reflects an increase in the MK-801 association rate even though protons reduce channel open probability and thus MK-801 access to its binding site. Allosteric modulators that alter pH sensitivity alter the potency of MK-801, supporting the interpretation that the pH sensitivity of MK-801 binding reflects the changes at the proton sensor rather than a secondary effect of pH. These data suggest a tight coupling between the proton sensor and the ion channel gate as well as unique subunit-specific mechanisms of channel block.