Pozzo Miller L D, Petrozzino J J, Connor J A
Roche Institute of Molecular Biology, Roche Research Center, Nutley, New Jersey 07110-1199, USA.
J Neurosci. 1995 Dec;15(12):8320-30. doi: 10.1523/JNEUROSCI.15-12-08320.1995.
Synaptic activation in the presence of competitive (D,L-APV,CNQX) and noncompetitive (MK-801,GYKI-52466) ionotropic glutamate receptor antagonists induced fast (10-90% rise time of 15-30 msec) postsynaptic responses in CA3 pyramidal neurons from acute and cultured hippocampal slices. Postsynaptic currents were studied extensively in slice cultures, and displayed a linear current-voltage relationship, with a reversal potential between 0 mV and +10 mV, suggesting the activation of a nonselective cationic conductance. Inhibition of the GTPase cycle by intracellular perfusion with the nonhydrolyzable analog of GDP, GDP beta S, blocked the fast postsynaptic responses evoked in ionotropic antagonists, as well as baclofen-mediated outward K+ currents, known to be mediated by G protein-coupled GABAB receptors. Intracellular perfusion with GDP beta S did not affect the AMPA/kainate component of the synaptic currents. Irreversible activation of G proteins by intracellular perfusion with the nonhydrolyzable analog of GTP, GMP-PNP, occluded the baclofen responses, and evoked an inward current, consistent with the synaptically mediated conductance. Incubation of the slice cultures in pertussis toxin for 72 hr blocked baclofen-induced outward K+ currents, while the fast postsynaptic currents remained. The metabotropic glutamate receptor (mGluR) agonists 1S,3R-ACPD and 1S,3S-ACPD induced an inward current in the presence of the ionotropic antagonists, and occluded the fast EPSCs. The fast EPSCs were partially blocked by the mGluR antagonists L-AP3 and (+)MCPG, but there was differential antagonists sensitivity in two pathways stimulated (CA3 stratum radiatum vs CA3 stratum oriens). These data suggest that fast postsynaptic responses evoked in the presence of ionotropic glutamate receptor antagonists are mediated by G protein-coupled mGluRs linked to nonselective cationic channels.
在竞争性（D，L - APV，CNQX）和非竞争性（MK - 801，GYKI - 52466）离子型谷氨酸受体拮抗剂存在的情况下，突触激活在急性和培养的海马切片的CA3锥体神经元中诱导了快速（10 - 90%上升时间为15 - 30毫秒）的突触后反应。在切片培养物中对突触后电流进行了广泛研究，其显示出线性电流 - 电压关系，反转电位在0 mV和 + 10 mV之间，表明激活了非选择性阳离子电导。通过细胞内灌注不可水解的GDP类似物GDPβS抑制GTP酶循环，阻断了离子型拮抗剂诱发的快速突触后反应以及已知由G蛋白偶联的GABAB受体介导的巴氯芬介导的外向K +电流。用GDPβS进行细胞内灌注不影响突触电流的AMPA/海人藻酸成分。通过细胞内灌注不可水解的GTP类似物GMP - PNP不可逆地激活G蛋白，阻断了巴氯芬反应，并诱发了内向电流，这与突触介导的电导一致。将切片培养物在百日咳毒素中孵育72小时可阻断巴氯芬诱导的外向K +电流，而快速突触后电流仍然存在。代谢型谷氨酸受体（mGluR）激动剂1S，3R - ACPD和1S，3S - ACPD在离子型拮抗剂存在的情况下诱导了内向电流，并阻断了快速兴奋性突触后电流（fast EPSCs）。快速兴奋性突触后电流被mGluR拮抗剂L - AP3和（+）MCPG部分阻断，但在两条受刺激的通路（CA3辐射层与CA3原层）中存在拮抗剂敏感性差异。这些数据表明，在离子型谷氨酸受体拮抗剂存在的情况下诱发的快速突触后反应是由与非选择性阳离子通道相连的G蛋白偶联mGluR介导的。
