Rat α6β2δ GABAA receptors exhibit two distinct and separable agonist affinities
Rat α6β2δ GABAA receptors exhibit two distinct and separable agonist affinities
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DOI：
10.1113/jphysiol.2007.132886
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发表时间：
2007-06-15
影响因子：
5.5
通讯作者：
Amin, Jahanshah
中科院分区：
文献类型：
--
作者：
Hadley, Stephen H.;Amin, Jahanshah
大鼠运动学习的开始与小脑颗粒神经元中含有α（6）和δ亚单位的GABA（A）受体的排他性表达相一致。这种发展在时间上与通过含α（6）的GABA（A）受体的自发活性氯电流的存在相关，称为紧张性抑制。在这里，我们报告说，α（6），β（2）和δ亚基的共表达产生的受体通道，具有两个不同的和可分离的激动剂亲和力的状态，一个表现出微摩尔和其他纳摩尔的GABA亲和力。高亲和力状态与显著水平的自发通道活性相关。增加表达水平或β（2）与α（6）和δ亚基的比例增加了高亲和力状态的流行。在相同表达水平下对α（6）β（2）δ、α（1）β（2）δ、α（6）β（2）γ（2）、α（1）β（2）γ（2）和α（4）β（2）δ受体的比较研究表明，自发通道活性的显著水平唯一地归因于α（6）β（2）δ受体。由α（6）β（2）δ受体表达引起的自发通道活动的药理学与强直性抑制相对应。例如，GABA（A）受体拮抗剂，包括呋塞米，阻断了自发电流。此外，神经活性类固醇5 α-THDOC和经典的甘氨酸受体激动剂β-丙氨酸和牛磺酸以高效力直接激活α（6）β（2）δ受体。GABA依赖性激活结构域（β（Y157 F））内的特定突变损害α（6）β（Y157 F）δ受体中GABA激动剂活性的低亲和力和高亲和力组分，但不减弱自发电流。相比之下，位于δ亚基的第二和第三跨膜区段之间的突变（δ（R287 M））显著减少了纳摩尔组分和自发活性。α（6）β（2）δ受体的高亲和力状态调节颗粒神经元活动的可能性以及影响其表达的潜在机制进行了讨论。
The onset of motor learning in rats coincides with exclusive expression of GABA(A) receptors containing alpha(6) and delta subunits in the granule neurons of the cerebellum. This development temporally correlates with the presence of a spontaneously active chloride current through alpha(6)-containing GABA(A) receptors, known as tonic inhibition. Here we report that the coexpression of alpha(6), beta(2), and delta subunits produced receptor-channels which possessed two distinct and separable states of agonist affinity, one exhibiting micromolar and the other nanomolar affinities for GABA. The high-affinity state was associated with a significant level of spontaneous channel activity. Increasing the level of expression or the ratio of beta(2) to alpha(6) and delta subunits increased the prevalence of the high-affinity state. Comparative studies of alpha(6)beta(2)delta, alpha(1)beta(2)delta, alpha(6)beta(2)gamma(2), alpha(1)beta(2)gamma(2) and alpha(4)beta(2)delta receptors under equivalent levels of expression demonstrated that the significant level of spontaneous channel activity is uniquely attributable to alpha(6)beta(2)delta receptors. The pharmacology of spontaneous channel activity arising from alpha(6)beta(2)delta receptor expression corresponded to that of tonic inhibition. For example, GABA(A) receptor antagonists, including furosemide, blocked the spontaneous current. Further, the neuroactive steroid 5 alpha-THDOC and classical glycine receptor agonists beta-alanine and taurine directly activated alpha(6)beta(2)delta receptors with high potency. Specific mutation within the GABA-dependent activation domain (beta(Y157F)) impaired both low- and high-affinity components of GABA agonist activity in alpha(6)beta(Y157F)delta receptors, but did not attenuate the spontaneous current. In comparison, a mutation located between the second and third transmembrane segments of the delta subunit (delta(R287M)) significantly diminished the nanomolar component and the spontaneous activity. The possibility that the high affinity state of the alpha(6)beta(2)delta receptor modulates the granule neuron activity as well as potential mechanisms affecting its expression are discussed.