Yang Tsung-Tair, Wang Su-Jane
Department of Psychiatry, Cardinal Tien Hospital, Taipei, Taiwan.
J Pharmacol Exp Ther. 2009 Oct;331(1):244-54. doi: 10.1124/jpet.109.155176. Epub 2009 Jul 23.
Pyridoxine (vitamin B(6)) protects neurons against neurotoxicity. An excessive release of glutamate is widely considered to be one of the molecular mechanisms of neuronal damage in several neurological diseases. We investigated whether pyridoxine affected glutamate release in rat cerebral cortex nerve terminals (synaptosomes). Pyridoxine inhibited the release of glutamate that was evoked by exposing synaptosomes to the K(+) channel blocker 4-aminopyridine (4-AP), and this phenomenon was concentration-dependent. Inhibition of glutamate release by pyridoxine was prevented by the vesicular transporter inhibitor bafilomycin A1, or by chelating intraterminal Ca(2+), but was insensitive to DL-threo-beta-benzyl-oxyaspartate, a glutamate transporter inhibitor. Pyridoxine did not alter the resting synaptosomal membrane potential or 4-AP-mediated depolarization. Examination of the effect of pyridoxine on cytosolic [Ca(2+)] revealed that diminution of glutamate release could be attributed to a reduction in voltage-dependent Ca(2+) influx. Consistent with this, the pyridoxine-mediated inhibition of glutamate release was completely prevented by blocking the N- and P/Q-type Ca(2+) channels, but not by blocking intracellular Ca(2+) release or Na(+)/Ca(2+) exchange. Furthermore, the pyridoxine effect on 4-AP-evoked glutamate release was abolished by the protein kinase C (PKC) inhibitors bisindolylmaleimide I (GF109203X) or bisindolylmaleimide IX (Ro318220), and pyridoxine significantly decreased the 4-AP-induced phosphorylation of PKC, PKCalpha, and myristoylated alanine-rich C kinase substrate. Together, these results suggest that pyridoxine inhibits glutamate release from rat cortical synaptosomes, through the suppression of presynaptic voltage-dependent Ca(2+) entry and PKC activity.
吡哆醇（维生素B6）可保护神经元免受神经毒性。谷氨酸的过度释放被广泛认为是几种神经疾病中神经元损伤的分子机制之一。我们研究了吡哆醇是否会影响大鼠大脑皮层神经末梢（突触体）中谷氨酸的释放。吡哆醇抑制了将突触体暴露于钾离子通道阻滞剂4-氨基吡啶（4-AP）所诱发的谷氨酸释放，且这种现象呈浓度依赖性。吡哆醇对谷氨酸释放的抑制作用可被囊泡转运体抑制剂巴弗洛霉素A1或通过螯合末梢内的钙离子所阻止，但对谷氨酸转运体抑制剂DL-苏式-β-苄氧基天冬氨酸不敏感。吡哆醇不会改变静息突触体膜电位或4-AP介导的去极化。对吡哆醇对胞质钙离子浓度影响的研究表明，谷氨酸释放的减少可归因于电压依赖性钙离子内流的减少。与此一致的是，通过阻断N型和P/Q型钙离子通道可完全阻止吡哆醇介导的谷氨酸释放抑制作用，但阻断细胞内钙离子释放或钠/钙交换则不能。此外，蛋白激酶C（PKC）抑制剂双吲哚马来酰亚胺I（GF109203X）或双吲哚马来酰亚胺IX（Ro318220）可消除吡哆醇对4-AP诱发的谷氨酸释放的作用，且吡哆醇可显著降低4-AP诱导的PKC、PKCα和富含肉豆蔻酰化丙氨酸的C激酶底物的磷酸化。总之，这些结果表明，吡哆醇通过抑制突触前电压依赖性钙离子内流和PKC活性来抑制大鼠皮层突触体中谷氨酸的释放。
