Two distinct mechanisms, differentially affected by excitatory amino acids, trigger GABA release from fetal mouse striatal neurons in primary culture.
The mechanisms leading to Ca2+-dependent and Ca2+-independent GABA release were studied on highly purified striatal neurons developed in primary culture. Ca2+-dependent GABA release, which represents about 75% of the 56 mM K+ effect was totally inhibited when striatal neurons were first exposed to tetanus toxin (TnTx) (10 micrograms/ml) for 24 hr. The K+ effect was potentiated when 1 mM nipecotic acid (an inhibitor of the GABA uptake system) was added during the stimulation period or when Na+ was replaced by Li+. However, no difference in the GABA release measured under high-K+ conditions was observed after a 22 min preincubation of the neurons in a medium containing nipecotic acid or Li+. Replacement of Cl- ions by SO4(2-) did not modify K+-evoked GABA release. Ca2+-independent GABA release was stimulated by veratridine (20 microM), ouabain (3 mM), and monensin (20 microM), as well as the excitatory amino acids glutamate (100 microM), N-methyl-D-aspartate (100 microM), quisqualate (10 microM), and kainate (1 mM), drugs known to increase intracellular Na+ concentration. The veratridine- or glutamate-evoked GABA release was neither inhibited when intracellular Ca2+ content was reduced by more than 90% nor by treatment of the neurons to TnTx. However, the Ca2+-independent GABA release elicited by veratridine was inhibited by preincubation of the neurons in a medium containing 1 mM nipectotic acid and in a medium containing Li+ instead of Na+ or SO4(2-) instead of Cl-. These results strongly suggest that 2 different GABA release mechanisms exist in striatal neurons.(ABSTRACT TRUNCATED AT 250 WORDS)
Pin
J P
JP
Centre CNRS-INSERM de Pharmacologie-Endocrinologie, Montpellier, France.
Bockaert
J
J
D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D001696:Biomechanical Phenomena; D002118:Calcium / Q000502:physiology; D002478:Cells, Cultured; D002712:Chlorides / Q000502:physiology; D003342:Corpus Striatum / Q000166:cytology / Q000378:metabolism*; D005333:Fetus / Q000378:metabolism; D008094:Lithium / Q000494:pharmacology; D051379:Mice; D008815:Mice, Inbred Strains; D009457:Neuroglia / Q000378:metabolism; D009474:Neurons / Q000201:enzymology / Q000378:metabolism*; D009557:Nipecotic Acids / Q000494:pharmacology; D011392:Proline / Q000031:analogs & derivatives*; D015290:Second Messenger Systems; D013744:Tetanus Toxin / Q000494:pharmacology; D014701:Veratridine / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D000596:Amino Acids; D002712:Chlorides; D009557:Nipecotic Acids; D013744:Tetanus Toxin; C030278:nipecotic acid; D005680:gamma-Aminobutyric Acid; D014701:Veratridine; D011392:Proline; D008094:Lithium; C010983:homoproline; D002118:Calcium