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Depolarization‐induced release of [ 3 H] d ‐aspartate from GABAergic neurons caused by reversal of glutamate transporters
Author(s) -
Jensen Jette B.,
Pickering Darryl S.,
Schousboe Arne
Publication year - 2000
Publication title -
international journal of developmental neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.761
H-Index - 88
eISSN - 1873-474X
pISSN - 0736-5748
DOI - 10.1016/s0736-5748(99)00099-4
Subject(s) - ampa receptor , glutamate receptor , depolarization , kainate receptor , gabaergic , chemistry , glutamatergic , biophysics , nmda receptor , nbqx , excitatory postsynaptic potential , population , receptor , biochemistry , biology , medicine , environmental health
Cultured neocortical neurons, which predominantly consist of GABAergic neurons exhibit a pronounced stimulus‐coupled GABA release. Since the cultures may contain a small population of glutamatergic neurons and the GABAergic neurons have a high content of glutamate it was of interest to examine if glutamate in addition to γ‐aminobutyric acid (GABA) could be released from these cultures. The neurons were preloaded with [ 3 H] d ‐aspartate and subsequently its release was followed during depolarization induced by a high potassium concentration or the α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptor agonists, AMPA and kainate. Depolarization of the neurons with 55 mM potassium increased the release of [ 3 H] d ‐aspartate by more than 10‐fold. When the non‐specific calcium‐channel blockers cobalt or lanthanum were included in the stimulation buffer with potassium, the release of [ 3 H] d ‐aspartate was decreased by about 40%. These results indicated that some of the released [ 3 H] d ‐aspartate might originate from a vesicular pool. When AMPA was applied to the neurons, the release of [ 3 H] d ‐aspartate was increased 2‐fold and could not be prevented or decreased by addition of cobalt. Since AMPA has a rapid desensitizing effect on AMPA receptors, it was examined whether AMPA under non‐desensitizing conditions was able to induce an increased release of [ 3 H] d ‐aspartate as compared to the conditions of applying AMPA alone. The desensitization of AMPA receptors was blocked by 6‐chloro‐3,4‐dihydro‐3‐(2‐norbornen‐5‐yl)‐2H‐1,2,4‐benzothiadiazine‐7‐sulphonamide‐1,1‐dioxide (cyclothiazide). Under the non‐desensitizing conditions, the AMPA‐induced release of [ 3 H] d ‐aspartate was highly enhanced showing about a 10‐fold increase over basal release. Addition of cobalt or lanthanum did not decrease the amount of [ 3 H] d ‐aspartate released, indicating that the release originated from a cytoplasmic pool. Kainate, which induces an almost non‐desensitizing effect on AMPA receptors, showed similar results as observed for AMPA under non‐desensitizing conditions. The NMDA receptor antagonist (5 R ,10 S )‐(+)‐5‐methyl‐10,11‐dihydro‐5H‐dibenzo[a,d]cyclohepten‐5,10‐imine (MK‐801) had only minor effects on the [ 3 H] d ‐aspartate release induced by AMPA and kainate. Thus, the depolarization‐induced release of [ 3 H] d ‐aspartate from cultured GABAergic neurons appears to be caused mainly by reversal of the glutamate transporters.