Second Messengers, Trafficking-Related Proteins, and Amino Acid Residues that Contribute to the Functional Regulation of the Rat Brain GABA Transporter GAT1

Quick, Michael W.; Corey, Janis L.; Davidson, Norman; Lester, Henry A.

doi:10.1523/jneurosci.17-09-02967.1997

Cited by 135 publications

(120 citation statements)

References 57 publications

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“…5B, E). This rectification is characteristic of GAT-associated currents (Quick et al, 1997). In contrast, the sustained outward current increased at depolarizing values and reversed at Ϫ75 mV (Fig.…”

Section: Effects Of Gaba In Cultured X-organ Cellsmentioning

confidence: 83%

Expression and Functional Characterization of GABA Transporters in Crayfish Neurosecretory Cells

et al. 2002

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The effect of GABA on membrane potential and ionic currents of X-organ neurons isolated from the crayfish eyestalk was investigated. Under voltage-clamp conditions, GABA elicited an inward Na ϩ current followed by a sustained outward chloride current. Sodium current was partially blocked in a dose-dependent manner by antagonists of GABA plasma membrane transporters such as ␤-alanine, nipecotic acid, 1-[2([(diphenylmethylene)imino]oxy)ethyl]-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid hydrochloride (NO 711), and SKF89976-A at concentrations between 1 and 100 M. This current was totally blocked by the combined application of NO 711 (5 M) and ␤-alanine (50 M). We obtained an EC 50 of 5 M and a Hill coefficient of 0.97 for the GABA transport mediated response. These results together with studies of immunolocalization using antibodies against neuronal vertebrate GABA transporters (GATs) indicate the presence of GAT-1-and GAT-3-like proteins in X-organ neurons. To isolate the sustained outward Cl Ϫ current, extracellular free sodium solution was used to minimize the contribution of GAT activity. We concluded that this current was caused by the activation of GABA A -like receptors with an EC 50 of 10 M and a Hill number of 1.7.To assign a functional role to the GATs in the X-organ sinus gland system, we determine the GABA concentration (0.46-0.15 M) in hemolymph samples using HPLC.In summary, our results suggest that a sodium-dependent electrogenic GABA uptake mechanism has a direct influence on the excitability of the X-organ neurons, maintaining an excitatory tone that is dependent on the circulating GABA level.

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Section: Effects Of Gaba In Cultured X-organ Cellsmentioning

confidence: 83%

Expression and Functional Characterization of GABA Transporters in Crayfish Neurosecretory Cells

et al. 2002

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“…To understand the extent of this influence, it is essential to understand the mechanisms underlying subcellular transporter trafficking. We and others have previously isolated transporter-containing synaptic-like vesicles that are potential mediators of transporter trafficking in axon terminals (10), and we have identified many signaling molecules that regulate subcellular transporter redistribution (12,14,15,22,24,28). In this report, by using a modified biotinylation assay to study GAT1 trafficking, (i) we defined an acutely recycling pool of GAT1 in cortical neurons that, in the basal state, comprises approximately one-third of total cellular GAT1; (ii) we measured the exocytosis rate (r exo ϭ 0.7 min Ϫ1 ) and the endocytosis rate (r endo ϭ 1.1 min Ϫ1 ) of acutely recycling GAT1 in the basal state; and (iii) we demonstrated that distinct transporter redistribution signals exert their effects by differentially regulating the recycling pool size or selectively uncoupling rates of exocytosis and endocytosis.…”

Section: Discussionmentioning

confidence: 99%

Trafficking of the Plasma Membrane γ-Aminobutyric Acid Transporter GAT1

Wang¹,

Quick

2005

Journal of Biological Chemistry

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Plasma membrane neurotransmitter transporters rapidly traffic to and from the cell surface in neurons. This trafficking may be important in regulating neuronal signaling. Such regulation will be subject to the number of trafficking transporters and their trafficking rates. In the present study, we define an acutely recycling pool of endogenous ␥-aminobutyric acid transporters (GAT1) in cortical neurons that comprises approximately one-third of total cellular GAT1. Kinetic analysis of this pool estimates exocytosis and endocytosis time constants of 1.6 and 0.9 min, respectively, and thus approximately one-third of the recycling pool is plasma membrane resident in the basal state. Recent evidence shows that GAT1 substrates, second messengers, and interacting proteins regulate GAT1 trafficking. These triggers could act by altering trafficking rates or by changing the recycling pool size. In the present study we examine three GAT1 modulators. Calcium depletion decreases GAT1 surface expression by diminishing the recycling pool size. Sucrose increases GAT1 surface expression by blocking clathrin-and dynamin-dependent endocytosis, but it does not change the recycling pool size. Protein kinase C decreases surface GAT1 expression by increasing the endocytosis rate, but it does not change the exocytosis rate or the recycling pool size. Based upon estimates of GAT1 molecules in cortical boutons, the present data suggest that ϳ1000 transporters comprise the acutely recycling pool, of which 300 are on the surface in the basal state, and five transporters insert into the plasma membrane every second. This insertion could represent the fusion of one transporter-containing vesicle.

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“…Although the difference in sequence between A␤ (1-42) and A␤ (1-40) is only two residues of C terminus, A␤ (1-42) aggregates more rapidly than A␤ (1-40) (28). Like A␤ (1-42), A␤ (25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35), a biologically active, hydrophobic fragment of A␤ (29), is also highly prone to aggregation (30). This subfragment could also reproduce the effect of A␤ (1-42) (data not shown).…”

Section: A␤ Attenuates Glutamatergic Neurotransmission In Neuro-mentioning

confidence: 93%

“…the neuronal glutamate transporter EAAC1 expressed in C6 glioma (21), serotonin transporters expressed in HEK293 cells (33), the ␥-aminobutyric acid transporter GAT1 expressed in Xenopus oocytes (34), and dopamine transporters expressed in PC12 cells (35), it is also possible that the A␤ effect is achieved by an increase in GLAST proteins on the cell surface. This possibility was addressed by a membrane-impermeant biotinylation assay.…”

Section: A␤ Attenuates Glutamatergic Neurotransmission In Neuro-mentioning

confidence: 99%

β-Amyloid Enhances Glial Glutamate Uptake Activity and Attenuates Synaptic Efficacy

Ikegaya¹,

Matsuura²,

Ueno

et al. 2002

Journal of Biological Chemistry

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Although amyloid ␤-protein (A␤) has long been implicated in the pathogenesis of Alzheimer's disease, little is known about the mechanism by which A␤ causes dementia. A␤ leads to neuronal cell death in vivo and in vitro, but recent evidence suggests that the property of the amnesic characteristic of Alzheimer's disease can be explained by a malfunction of synapses rather than a loss of neurons. Here we show that prolonged treatment with A␤ augments the glutamate clearance ability of cultured astrocytes and induces a dramatic decrease in glutamatergic synaptic activity of neurons cocultured with the astrocytes. Biotinylation assay revealed that the enhancement of glutamate uptake activity was associated with an increase in cell-surface expression of GLAST, a subtype of glial glutamate transporters, without apparent changes in the total amount of GLAST. This phenomenon was blocked efficiently by actindisrupting agents. Thus, A␤-induced actin-dependent GLAST redistribution and relevant synaptic malfunction may be a cellular basis for the amnesia of Alzheimer's disease.Amyloid ␤-protein (A␤), 1 a peptide with 40 -42 residues, is a main element of senile plaque, a hallmark of Alzheimer's disease (AD) (1, 2), and is accumulated highly in the forebrain of AD patients, as well as transgenic mice overexpressing mutant ␤-amyloid precursor protein (␤APP), which develop AD-like pathology (3, 4). Although numerous studies showed that exogenously applied or endogenously produced A␤ leads to neuronal cell death, the amnesic feature of AD cannot be explained by the neuronal loss alone (5). Indeed, accumulating evidence indicates that A␤ induces severe impairment of excitatory neurotransmission in the hippocampus (6 -8) and thereby may cause memory deficits (9). In mutant ␤APP transgenic mice, such synaptic malfunction often appears in advance of A␤ plaque formation (10, 11), and cognitive deterioration is also observed without apparent neurodegeneration (4, 12). A␤-induced synaptic deterioration rather than neuronal loss is, therefore, likely to be a main cause of early AD dementia (5, 13). However, the mechanisms by which A␤ causes such synaptic malfunction remain to be elucidated.Excitatory neurotransmission is tightly regulated by a rapid clearance of the neurotransmitter glutamate from the extracellular milieu through Na ϩ -dependent L-glutamate transporters that are expressed on astrocytes, i.e. GLAST and GLT-1 (14, 15). We therefore investigated the effect of A␤ on glutamate uptake activity in cultured cortical astrocytes. Here we show for the first time that A␤ ending at 42 residues (A␤ (1-42)) induces an increase in the activity of GLAST. This work further demonstrates that A␤ (1-42) stimulates actin-dependent GLAST redistribution from subcellular compartment to the cell surface. Such up-regulation of GLAST function may attenuate glutamatergic synaptic efficacy. EXPERIMENTAL PROCEDURESMaterials-Chemically synthesized A␤ (1-40) and A␤ (1-42) were gifts from Dr. T. Shirasawa (Department of Molecular Genetics, Tokyo Metropo...

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Second Messengers, Trafficking-Related Proteins, and Amino Acid Residues that Contribute to the Functional Regulation of the Rat Brain GABA Transporter GAT1

Cited by 135 publications

References 57 publications

Expression and Functional Characterization of GABA Transporters in Crayfish Neurosecretory Cells

Expression and Functional Characterization of GABA Transporters in Crayfish Neurosecretory Cells

Trafficking of the Plasma Membrane γ-Aminobutyric Acid Transporter GAT1

β-Amyloid Enhances Glial Glutamate Uptake Activity and Attenuates Synaptic Efficacy

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