Protons Regulate Vesicular Glutamate Transporters through an Allosteric Mechanism

Eriksen, Jacob; Chang, Roger; McGregor, Matt; Silm, Kätlin; Suzuki, Toshiharu; Edwards, Robert H.

doi:10.1016/j.neuron.2016.03.026

Cited by 65 publications

(145 citation statements)

References 56 publications

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“…The remainder of the pH difference (∼0.2 pH units) remains elusive, but it may be because of vesicle acidification as a result of glutamate transport (7) or the Cl -conductance that is intrinsic to VGLUTs (22,(35)(36)(37). Therefore, our results support the notion that, despite the similarity in molecular composition between glutamatergic and GABAergic SVs, SVs acquire unique properties because of the expression of their respective neurotransmitter transporters (5,6,21).…”

Section: Discussionsupporting

confidence: 76%

Unique pH dynamics in GABAergic synaptic vesicles illuminates the mechanism and kinetics of GABA loading

Egashira

Miki

Watanabe

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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GABA acts as the major inhibitory neurotransmitter in the mammalian brain, shaping neuronal and circuit activity. For sustained synaptic transmission, synaptic vesicles (SVs) are required to be recycled and refilled with neurotransmitters using an H + electrochemical gradient. However, neither the mechanism underlying vesicular GABA uptake nor the kinetics of GABA loading in living neurons have been fully elucidated. To characterize the process of GABA uptake into SVs in functional synapses, we monitored luminal pH of GABAergic SVs separately from that of excitatory glutamatergic SVs in cultured hippocampal neurons. By using a pH sensor optimal for the SV lumen, we found that GABAergic SVs exhibited an unexpectedly higher resting pH (∼6.4) than glutamatergic SVs (pH ∼5.8). Moreover, unlike glutamatergic SVs, GABAergic SVs displayed unique pH dynamics after endocytosis that involved initial overacidification and subsequent alkalization that restored their resting pH. GABAergic SVs that lacked the vesicular GABA transporter (VGAT) did not show the pH overshoot and acidified further to ∼6.0. Comparison of luminal pH dynamics in the presence or absence of VGAT showed that VGAT operates as a GABA/H + exchanger, which is continuously required to offset GABA leakage. Furthermore, the kinetics of GABA transport was slower (τ > 20 s at physiological temperature) than that of glutamate uptake and may exceed the time required for reuse of exocytosed SVs, allowing reuse of incompletely filled vesicles in the presence of high demand for inhibitory transmission.synaptic vesicle | VGAT | inhibitory neuron

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Section: Discussionsupporting

confidence: 76%

Unique pH dynamics in GABAergic synaptic vesicles illuminates the mechanism and kinetics of GABA loading

Egashira

Miki

Watanabe

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…In agreement with this notion, our recent single‐vesicle imaging approach showed significant K + /H + exchange in glutamatergic vesicles . Most recently, electrophysiological recordings demonstrated that luminal protons allosterically stimulate VGLUTs .…”

Section: Neurotransmitter Uptake Machinerysupporting

confidence: 76%

“…Prospects & Overviews .... exchange in glutamatergic vesicles [49]. Most recently, electrophysiological recordings demonstrated that luminal protons allosterically stimulate VGLUTs [68].…”

Section: Glutamate and Atpmentioning

confidence: 99%

Proton electrochemical gradient: Driving and regulating neurotransmitter uptake

2017

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Accumulation of neurotransmitters in the lumen of synaptic vesicles (SVs) relies on the activity of the vacuolar-type H -ATPase. This pump drives protons into the lumen, generating a proton electrochemical gradient (Δμ ) across the membrane. Recent work has demonstrated that the balance between the chemical (ΔpH) and electrical (ΔΨ) components of Δμ is regulated differently by some distinct vesicle types. As different neurotransmitter transporters use ΔpH and ΔΨ with different relative efficiencies, regulation of this gradient balance has the potential to influence neurotransmitter uptake. Nevertheless, the underlying mechanisms responsible for this regulation remain poorly understood. In this review, we provide an overview of current neurotransmitter uptake models, with a particular emphasis on the distinct roles of the electrical and chemical gradients and current hypotheses for regulatory mechanisms.

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“…Interestingly, Cl − substitution with gluconate, a VGLUT-impermeant anion, significantly delayed the time course of hyperacidification. This delay may be explained by previous studies showing that Cl − modulates VGLUT activity, where decreasing external Cl − concentrations significantly reduces VGLUT2-associated currents (Eriksen et al, 2016). Thus, it is possible that under low Cl − conditions, VGLUT-dependent hyperacidification is delayed because glutamate transport by VGLUT is slowed.…”

Section: Discussionmentioning

confidence: 83%

“…Since there are multiple routes for vesicular Cl − flux besides ClCs (Eriksen et al, 2016), we examined Cl − ’s potential contribution to depolarization-induced DA vesicle hyperacidification more generally. We halved the extracellular Cl − present during high K + neuronal stimulation by isosmotically substituting Cl − with gluconate (20 mM Cl − ; Figure 3C).…”

Section: Resultsmentioning

confidence: 99%

Neuronal Depolarization Drives Increased Dopamine Synaptic Vesicle Loading via VGLUT

Aguilar

Dunn

Mingote

et al. 2017

Neuron

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SUMMARY The ability of presynaptic dopamine terminals to tune neurotransmitter release to meet the demands of neuronal activity is critical to neurotransmission. Although vesicle content has been assumed to be static, in vitro data increasingly suggest that cell activity modulates vesicle content. Here, we use a coordinated genetic, pharmacological, and imaging approach in Drosophila to study the presynaptic machinery responsible for these vesicular processes in vivo. We show that cell depolarization increases synaptic vesicle dopamine content prior to release via vesicular hyperacidification. This depolarization-induced hyperacidification is mediated by the vesicular glutamate transporter (VGLUT). Remarkably, both depolarization-induced dopamine vesicle hyperacidification and its dependence on VGLUT2 are seen in ventral midbrain dopamine neurons in the mouse. Together, these data suggest that in response to depolarization, dopamine vesicles utilize a cascade of vesicular transporters to dynamically increase the vesicular pH gradient, thereby increasing dopamine vesicle content.

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Protons Regulate Vesicular Glutamate Transporters through an Allosteric Mechanism

Cited by 65 publications

References 56 publications

Unique pH dynamics in GABAergic synaptic vesicles illuminates the mechanism and kinetics of GABA loading

Unique pH dynamics in GABAergic synaptic vesicles illuminates the mechanism and kinetics of GABA loading

Proton electrochemical gradient: Driving and regulating neurotransmitter uptake

Neuronal Depolarization Drives Increased Dopamine Synaptic Vesicle Loading via VGLUT

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