Unitary Properties of AMPA Receptors with Reduced Desensitization.
Unitary Properties of AMPA Receptors with Reduced Desensitization.
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降低脱敏作用的 AMPA 受体的单一特性。
DOI：
10.1016/j.bpj.2017.07.030
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发表时间：
2017
影响因子：
3.4
通讯作者：
Howe,JamesR
中科院分区：
文献类型：
--
作者：
Zhang,Wei;Eibl,Clarissa;Weeks,AutumnM;Riva,Irene;Li,Yan-Jun;Plested,AndrewJR;Howe,JamesR
野生型AMPA受体表现出快速脱敏的表型特征。许多研究指出，细胞外配体结合域对之间的二聚体界面是控制受体脱敏速率的关键区域。然而，在孔形成区域的细胞外端（假定的离子通道门附近）的突变也被证明可以改变脱敏。在这里，我们报道了单个GluA4受体携带两种突变中的一种的行为，这两种突变在集合电流水平上大大降低了脱敏性：二聚体界面突变L484Y和M3（第二个真正的跨膜螺旋）的胞外端urcher突变（A623T, GluA4- lc）。对只有一个活性受体的斑块的单一电流的分析表明，每个突变都大大延长了开放的爆发，而不延长单个开放的表观持续时间。每个突变降低了单个受体访问脱敏状态的频率，但两个突变受体仍然每秒多次脱敏。环噻嗪（CTZ）降低了野生型受体和两种突变型受体的脱敏性。对关闭时间分布的分析揭示了一种对CTZ具有抗性的短暂脱敏形式，对GluA4-Lc受体尤其突出。尽管降低了GluA4 L484Y受体的脱敏作用，但CTZ通过GluA2和GluA4 LY受体突变体降低了集合电流的振幅。对gla2 L483Y配体结合域二聚体与谷氨酸复合物的单通道分析和比较结果表明，CTZ与二聚体界面的结合阻止了LY突变对受体激活的调节作用，导致大电导底态的流行减少，这是导致集合电流振幅下降的原因。总之，研究结果表明，群体电流中相似的非脱敏ampa受体表型可能产生于不同的潜在分子机制，产生不同类型的单一活性。
Wild-type AMPA receptors display a characteristic rapidly desensitizing phenotype. Many studies point to the dimer interface between pairs of extracellular ligand binding domains as the key region controlling the rate at which the receptors desensitize. However, mutations at the extracellular end of the pore-forming regions (near the putative ion channel gate) have also been shown to alter desensitization. Here we report the behavior of single GluA4 receptors carrying one of two mutations that greatly reduce desensitization at the level of ensemble currents: the dimer interface mutation L484Y and theLurchermutation (A623T, GluA4-Lc) in the extracellular end of M3 (the second true transmembrane helix). Analysis of unitary currents in patches with just one active receptor showed that each mutation greatly prolongs bursts of openings without prolonging the apparent duration of individual openings. Each mutation decreases the frequency with which individual receptors visit desensitized states, but both mutant receptors still desensitize multiple times per second. Cyclothiazide (CTZ) reduced desensitization of wild-type receptors and both types of mutant receptor. Analysis of shut-time distributions revealed a form of short-lived desensitization that was resistant to CTZ and was especially prominent for GluA4-Lc receptors. Despite reducing desensitization of GluA4 L484Y receptors, CTZ decreased the amplitude of ensemble currents through GluA2 and GluA4 LY receptor mutants. Single-channel analysis and comparison of the GluA2 L483Y ligand binding domain dimer in complex with glutamate with and without CTZ is consistent with the conclusion that CTZ binding to the dimer interface prevents effects of the LY mutation to modulate receptor activation, resulting in a reduction in the prevalence of large-conductance substates that accounts for the decrease in ensemble current amplitudes. Together, the results show that similar nondesensitizing AMPA-receptor phenotypes of population currents can arise from distinct underlying molecular mechanisms that produce different types of unitary activity.