Steady states, charge movements, and rates for a cloned GABA transporter expressed in Xenopus oocytes

Mager, Sela; Naeve, Janis; Quick, Michael W.; Labarca, Cesar; Davidson, Norman; Lester, Henry A.

doi:10.1016/0896-6273(93)90309-f

Cited by 312 publications

(465 citation statements)

References 21 publications

Supporting

Mentioning

399

Contrasting

Unclassified

Order By: Relevance

“…In agreement with previous reports in which the electrogenic uptake of GABA by GAT-1 expressed in Xenopus oocytes was explored (Kavanaugh et al, 1992;Mager et al, 1993), our study demonstrates that the Hill coefficient for GABA transporters in X-organ neurons is correlated with voltage-clamp current measurements, suggesting a stoichiometry of one net positive elementary charge per GABA molecule transported.…”

supporting

confidence: 80%

Expression and Functional Characterization of GABA Transporters in Crayfish Neurosecretory Cells

et al. 2002

View full text Add to dashboard Cite

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.

show abstract

supporting

confidence: 80%

Expression and Functional Characterization of GABA Transporters in Crayfish Neurosecretory Cells

et al. 2002

View full text Add to dashboard Cite

show abstract

“…This observation was in agreement with the result of immunohistochemical staining shown in Fig 3. Since only the elongated spermatids and spermatozoa in testis express GAT1 protein, it is evident that the difference of the staining intensity between lane 2 and 3 in Fig 1 is due to their difference in the relative GAT1 content in protein extracts. The existence of GAT1 can lead to the membrane depolarization which has been demonstrated by other studies [19], [20]. Meanwhile, membrane depolarization is also important for the initiation of the sperm AR [21], so we postulate a possible role of GAT1 in sperm AR.…”

Section: Cellular Localization Of Gat1 In Rat Testis and Spermsupporting

confidence: 52%

Identification of γ-aminobutyric acid transporter (GAT1) on the rat sperm

Yuan

2000

Cell Res

View full text Add to dashboard Cite

Some recent studies indicated that GABAergic system is involved in mammalian sperm acrosome reaction (AR), but direct evidence pertaining to the expression of gat1 in mammalian sperm is not yet demonstrated. In this study, we evaluated the presence of 67kDa GAT1 protein and mRNA in rat testis by Western blotting and reverse transcription-polymerase chain reaction. Meanwhile, immunohistochemical and immunofluorescent analyses also identified GAT1 protein on the elongated spermatid and sperm. These results indicated that rat testis is a novel site of gat1 expression. Further studies should be taken to explore the role of GAT1 protein on sperm acrosome reaction.

show abstract

“…It will be important to explain these observations in terms of the molecular mechanisms of transporter function. The traditional view of the GABA transporter is that it is electrogenic, with a fixed stoichiometry of two sodium ions and one chloride ion transported per GABA molecule (Larsson et al, 1980;Guastella et al, 1990;Borden et al, 1992;Kavanaugh et al, 1992;Mager et al, 1993). However, measurements of current flow through artificially expressed GAT-1 suggest that the stoichiometry actually is not fixed.…”

Section: Functional Role Of the Gaba Transportermentioning

confidence: 99%

“…This approach has a slow response time and is not sensitive to small local concentrations of GABA at sites where it is functionally significant, such as within the synaptic cleft. The GABA transporter also has been studied by measuring current flow directly through the transporter (Malchow and Ripps, 1990;Mager et al, 1993;Cammack et al, 1994;Risso et al, 1996). The time course of these current measurements is fast, but it is difficult to correlate current flow with the functional effect, i.e., GABA receptor activation.…”

Section: Gaba a Receptor Activation As An Assay Of Gaba Releasementioning

confidence: 99%

“…If this were the case, antagonists of the GABA transporter should reduce the tonic GABA A receptor-mediated current induced by vigabatrin. To test this possibility, we used the GABA transporter antagonist SKF-89976a because it blocks influx and efflux through the transporter and has not been reported to cause heteroexchange release of GABA (Mager et al, 1993;Cammack et al, 1994).…”

Section: Tonic Gaba Efflux Was Mediated By the Gaba Transporter Operamentioning

confidence: 99%

See 1 more Smart Citation

GABA Transaminase Inhibition Induces Spontaneous and Enhances Depolarization-Evoked GABA Efflux via Reversal of the GABA Transporter

2001

View full text Add to dashboard Cite

The GABA transporter can reverse with depolarization, causing nonvesicular GABA release. However, this is thought to occur only under pathological conditions. Patch-clamp recordings were made from rat hippocampal neurons in primary cell cultures. Inhibition of GABA transaminase with the anticonvulsant ␥-vinyl GABA (vigabatrin; 0.05-100 M) resulted in a large leak current that was blocked by bicuculline (50 M). This leak current occurred in the absence of extracellular calcium and was blocked by the GABA transporter antagonist SKF-89976a (5 M). These results indicate that vigabatrin induces spontaneous GABA efflux from neighboring cells via reversal of GABA transporters, subsequently leading to the stimulation of GABA A receptors on the recorded neuron. The leak current increased slowly over 4 d of treatment with 100 M vigabatrin, at which time it reached an equivalent conductance of 9.0 Ϯ 4.9 nS. Blockade of glutamic acid decarboxylase with semicarbazide (2 mM) decreased the leak current that was induced by vigabatrin by 47%. In untreated cells, carrier-mediated GABA efflux did not occur spontaneously but was induced by an increase in [K ϩ ] o from 3 to as little as 6 mM. Vigabatrin enhanced this depolarization-evoked nonvesicular GABA release and also enhanced the heteroexchange release of GABA induced by nipecotate. Thus, the GABA transporter normally operates near its equilibrium and can be easily induced to reverse by an increase in cytosolic [GABA] or mild depolarization. We propose that this transporter-mediated nonvesicular GABA release plays an important role in neuronal inhibition under both physiological and pathophysiological conditions and is the target of some anticonvulsants.

show abstract

Steady states, charge movements, and rates for a cloned GABA transporter expressed in Xenopus oocytes

Cited by 312 publications

References 21 publications

Expression and Functional Characterization of GABA Transporters in Crayfish Neurosecretory Cells

Expression and Functional Characterization of GABA Transporters in Crayfish Neurosecretory Cells

Identification of γ-aminobutyric acid transporter (GAT1) on the rat sperm

GABA Transaminase Inhibition Induces Spontaneous and Enhances Depolarization-Evoked GABA Efflux via Reversal of the GABA Transporter

Contact Info

Product

Resources

About