Varoqui Helene, Schäfer Martin K H, Zhu Heming, Weihe Eberhard, Erickson Jeffrey D
Neuroscience Center and Department of Opthalmology, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112, USA.
J Neurosci. 2002 Jan 1;22(1):142-55. doi: 10.1523/JNEUROSCI.22-01-00142.2002.
Glutamate transport into synaptic vesicles is a prerequisite for its regulated neurosecretion. Here we functionally identify a second isoform of the vesicular glutamate transporter (VGLUT2) that was previously identified as a plasma membrane Na+-dependent inorganic phosphate transporter (differentiation-associated Na+/P(I) transporter). Studies using intracellular vesicles from transiently transfected PC12 cells indicate that uptake by VGLUT2 is highly selective for glutamate, is H+ dependent, and requires Cl- ion. Both the vesicular membrane potential (Deltapsi) and the proton gradient (DeltapH) are important driving forces for vesicular glutamate accumulation under physiological Cl- concentrations. Using an antibody specific for VGLUT2, we also find that this protein is enriched on synaptic vesicles and selective for a distinct class of glutamatergic nerve terminals. The pathway-specific, complementary expression of two different vesicular glutamate transporters suggests functional diversity in the regulation of vesicular release at excitatory synapses. Together, the two isoforms may account for the uptake of glutamate by synaptic vesicles from all central glutamatergic neurons.
谷氨酸转运到突触小泡中是其受调控的神经分泌的前提条件。在此，我们从功能上鉴定出了囊泡谷氨酸转运体（VGLUT2）的第二种亚型，该亚型先前被鉴定为质膜Na⁺依赖性无机磷酸转运体（分化相关Na⁺/P(i)转运体）。使用来自瞬时转染PC12细胞的细胞内小泡进行的研究表明，VGLUT2对谷氨酸的摄取具有高度选择性，依赖于H⁺，并且需要Cl⁻离子。在生理Cl⁻浓度下，囊泡膜电位（Δψ）和质子梯度（ΔpH）都是囊泡谷氨酸积累的重要驱动力。使用针对VGLUT2的特异性抗体，我们还发现该蛋白在突触小泡上富集，并且对一类独特的谷氨酸能神经末梢具有选择性。两种不同的囊泡谷氨酸转运体在途径特异性上的互补表达表明，在兴奋性突触处囊泡释放的调节中存在功能多样性。这两种亚型共同作用，可能解释了所有中枢谷氨酸能神经元的突触小泡对谷氨酸的摄取。
