title: Regulation of [gamma-3H]aminobutyric acid transport by Ca2+ in isolated synaptic plasma membrane vesicles.
abstract: We studied the effect of Ca2+ on the transport of the gamma-aminobutyric acid (GABA) by synaptic plasma membrane (SPM) vesicles isolated from sheep brain cortex and observed that intravesicular Ca2+ inhibits the [3H]GABA accumulation in a concentration-dependent manner. This inhibitory effect of Ca2+ exhibited two distinct components: one in the micromolar range of Ca2+ concentration, and the other in the millimolar range. Previous EGTA washing of the membranes, or incorporation of trifluoperazine into the vesicular space reduced the inhibitory action of Ca2+, particularly at low Ca2+ (1-5 microM). Okadaic acid (1 microM) also relieved the Ca2+ inhibition at low, but not at high Ca2+ concentrations (1 mM), whereas the calpain inhibitor I did not alter the effect of the low Ca2+, but it partially reduced (approximately 28%) the effect of Ca2+ in the millimolar range. The results indicate that the GABA transporter is regulated by low Ca2+ concentration (microM) and probably its effect is mediated by the (Ca2+ x calmodulin)-stimulated phosphatase 2B (calcineurin). In contrast, the GABA uptake inhibition observed at high Ca2+ concentrations (1 mM) is less specific, and probably it is partially related to the proteolytic activity of membrane bound calpain II.
authors.affiliation: Departamento de Biologia, Universidade de Aveiro, Portugal.
authors.forename: P P
authors.initials: PP
authors.lastname: Gonçalves
authors.forename: A P
authors.initials: AP
authors.lastname: Carvalho
authors.forename: M G
authors.initials: MG
authors.lastname: Vale
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism*; D002540:Cerebral Cortex / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D050485:GABA Plasma Membrane Transport Proteins; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism*; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; D012756:Sheep; D013570:Synaptic Membranes / Q000187:drug effects / Q000378:metabolism*; D014268:Trifluoperazine / Q000494:pharmacology; D014316:Tritium; D014634:Valinomycin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*; D003189:p-Methoxy-N-methylphenethylamine / Q000494:pharmacology
chemical_list: D002147:Calmodulin; D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; D014316:Tritium; D014634:Valinomycin; D014268:Trifluoperazine; D003189:p-Methoxy-N-methylphenethylamine; D004533:Egtazic Acid; D005680:gamma-Aminobutyric Acid; D015759:Ionomycin; D002118:Calcium