Excitatory amino acid-evoked release of [3H]GABA from hippocampal neurons in primary culture.
We investigated the release of gamma-[2,3-3H(N)]aminobutyric acid ([3H]GABA) from hippocampal neurons in primary cell culture. [3H]GABA release was stimulated by the excitatory amino acid neurotransmitter glutamate as well as by N-methyl-D-aspartate (NMDA) and kainate. Cell depolarization induced by raising [K+]o or by veratridine also stimulated [3H]GABA release. NMDA-induced release was completely blocked by 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP+), Mg2+ and Zn2+ whereas the release induced by glutamate and kainate was much less susceptible to inhibition by these substances. Furthermore, removal of external Ca2+ inhibited NMDA-induced release, but not that induced by glutamate, kainate, veratridine or 50 mM K+. Removal of external Na+ reduced [3H]GABA release evoked by all stimuli, but to different extents. All of the excitatory amino acids tested increased [Ca2+]i within hippocampal neurons as assessed by fura-2 based microspectrofluorimetry. This increase in [Ca2+]i was completely dependent on the presence of external Ca2+. These results suggest that Ca2+-dependent and -independent forms of GABA release from hippocampal interneurons may occur. [3H]GABA release evoked by glutamate, kainate, veratridine or 50 mM K+, appeared to be mediated by the reversal of electrogenic, Na+-coupled GABA uptake. Release was inhibited by nipecotic acid, an inhibitor of the Na+-coupled GABA uptake system. However, release induced by NMDA may also include a Ca2+-dependent component.
Harris
K M
KM
Department of Pharmacological and Physiological Sciences, University of Chicago, IL 60637.
Miller
R J
RJ
D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D002478:Cells, Cultured; D004987:Ethers / Q000494:pharmacology; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D006624:Hippocampus / Q000378:metabolism*; D015759:Ionomycin; D007608:Kainic Acid / Q000494:pharmacology*; D016202:N-Methylaspartate; D051381:Rats; D011919:Rats, Inbred Strains; D014701:Veratridine / Q000494:pharmacology; D015032:Zinc / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D004987:Ethers; D005971:Glutamates; D001224:Aspartic Acid; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D015759:Ionomycin; D016202:N-Methylaspartate; D014701:Veratridine; D015032:Zinc; D007608:Kainic Acid