title: High-affinity GABA uptake by neuronal GAT1 transporters provokes release of [(3)H]GABA by homoexchange and through GAT1-independent Ca(2+)-mediated mechanisms.
abstract: High-affinity uptake of GABA into nerve terminals may have functions other than recapture of the neurotransmitter. Synaptosomes purified from mouse cerebellum were prelabelled with [(3)H]GABA and then superfused with GABA and drugs selective for some presynaptic targets. Influx of GABA through GAT1 transporters stimulated efflux of [(3)H]GABA in a concentration-dependent manner (EC50 ∼ 3 μM). The efflux of the transmitter occurred in part by GAT1 reversal through the so called homoexchange. The ion fluxes (particularly Na(+) influx) accompanying GABA uptake triggered intraterminal Ca(2+) signals through both plasmalemmal Na(+)/Ca(2+) exchangers, sensitive to KB-R7943 or to ifenprodil and mitochondrial Na(+)/Ca(2+) exchangers, sensitive to CGP37157. These Ca(2+) signals likely facilitated GABA release from nerve terminals via niflumic acid- and NPPB-sensitive anion channels. The results show that GABA, at concentrations corresponding to the high-affinity uptake, can evoke GABA release which occurs in part by the expected GAT1-mediated homoexchange, while the transporter-independent component of the GABA uptake-evoked GABA release takes place by hitherto unsuspected mechanisms which include Na(+)/Ca(2+) exchangers and anion channels. The significance of the novel function of the GABA high-affinity uptake here identified deserves further multidisciplinary investigation.
authors.affiliation: Department of Pharmacy, Pharmacology and Toxicology Section, University of Genoa, Genoa, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Romei
authors.affiliation: Department of Pharmacy, Pharmacology and Toxicology Section, University of Genoa, Genoa, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Sabolla
authors.affiliation: Department of Pharmacy, Pharmacology and Toxicology Section, University of Genoa, Genoa, Italy; Center of Excellence for Biomedical Research, University of Genoa, Genoa, Italy; National Institute of Neuroscience, Genoa, Italy. Electronic address: lraiter@pharmatox.unige.it.
authors.forename: Luca
authors.initials: L
authors.lastname: Raiteri
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002412:Cations / Q000378:metabolism; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism; D050485:GABA Plasma Membrane Transport Proteins / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism; D008297:Male; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D002412:Cations; D050485:GABA Plasma Membrane Transport Proteins; D007473:Ion Channels; C493414:Slc6a1 protein, mouse; D019831:Sodium-Calcium Exchanger; D014316:Tritium; D005680:gamma-Aminobutyric Acid; D012964:Sodium; D002118:Calcium
keywords: Anion channels; GABA GAT1 transporter; GABA homoexchange; GABA release; Mitochondrial Na(+)/Ca(2+) exchanger; Plasmalemmal Na(+)/Ca(2+) exchanger