Canepari Marco, Auger Céline, Ogden David
National Institute for Medical Research, London NW7 1AA, United Kingdom.
J Neurosci. 2004 Apr 7;24(14):3563-73. doi: 10.1523/JNEUROSCI.5374-03.2004.
The slow EPSC (sEPSC) of cerebellar parallel fiber --> Purkinje neuron synapses is mediated by metabotropic glutamate receptor type 1 (mGluR1) activation of nonselective cation channels. Here, the channel properties were studied with uniform calibrated photorelease of L-glutamate with ionotropic receptors blocked, allowing isolation of postsynaptic processes, or with parallel fiber stimulation or mGluR1 agonist application. Evoked current and fluorescence from Ca(2+) indicators were recorded. Noise analysis of the mGluR1 current gave a single-channel conductance of 0.6 pS and showed low open probability at maximal mGluR1 activation. Similar small single-channel conductances were obtained with the mGluR1 agonist (S)-dihydroxyphenylglycine, with parallel fiber or climbing fiber stimulation. The mGluR1 current fluctuations were unaffected by potassium channel blockers. Photoreleased L-glutamate triggered a Ca(2+) concentration increase in the distal dendrites with a time course similar to that of the mGluR1 current. The proximal dendritic and somatic Ca(2+) changes were delayed with respect to the current. Ca(2+) channel blockers and the phospholipase Cdelta inhibitor 1-[6-[((17delta)-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl]-1H-pyrrole-2,5-dione, which inhibits mGluR1-activated intracellular Ca(2+) release, did not prevent the dendritic Ca(2+) concentration increase. Polyamine naphthylacetyl spermine and cationic adamantanes that block the pore of the channel were used to vary the mGluR1 current over a wide range in each cell but still at maximal mGluR1 activation. The Ca(2+) influx was inhibited in parallel with the current. The results show that the mGluR1-activated current and the sEPSC are attributable to small-conductance, low-open probability Ca(2+)-permeable cation channels that will mediate spine-specific Ca(2+) influx during the parallel fiber sEPSP.
小脑平行纤维与浦肯野神经元突触的慢兴奋性突触后电流（sEPSC）由代谢型谷氨酸受体1（mGluR1）激活非选择性阳离子通道介导。在此，通过在离子型受体被阻断的情况下均匀校准光释放L-谷氨酸来研究通道特性，从而分离突触后过程，或者通过平行纤维刺激或应用mGluR1激动剂来进行研究。记录诱发电流和来自Ca(2+)指示剂的荧光。对mGluR1电流的噪声分析得出单通道电导为0.6 pS，并显示在最大mGluR1激活时开放概率较低。使用mGluR1激动剂（S）-二羟基苯甘氨酸、平行纤维或攀缘纤维刺激也获得了类似的小单通道电导。mGluR1电流波动不受钾通道阻滞剂的影响。光释放的L-谷氨酸触发远端树突中Ca(2+)浓度升高，其时间进程与mGluR1电流相似。近端树突和体细胞的Ca(2+)变化相对于电流有所延迟。Ca(2+)通道阻滞剂和磷脂酶Cδ抑制剂1-[6-[((17δ)-3-甲氧基雌甾-1,3,5[10]-三烯-17-基)氨基]己基]-1H-吡咯-2,5-二酮可抑制mGluR1激活的细胞内Ca(2+)释放，但并不能阻止树突中Ca(2+)浓度升高。用于阻断通道孔的多胺萘乙酰精胺和阳离子金刚烷被用于在每个细胞中广泛改变mGluR1电流，但仍处于最大mGluR1激活状态。Ca(2+)内流与电流平行受到抑制。结果表明，mGluR1激活的电流和sEPSC归因于小电导、低开放概率的Ca(2+)通透阳离子通道，这些通道将在平行纤维sEPSP期间介导棘突特异性Ca(2+)内流。
