Potassium-stimulated release of [3H]taurine from cultured GABAergic and glutamatergic neurons.
The effect of depolarizing concentrations of potassium (56 mM) on the release of [3H]taurine was examined in two types of cultured neurons from mouse brain: cerebral cortex neurons, which are largely GABAergic, and cerebellar neurons, which after treatment with kainate consist almost entirely of glutamatergic granule cells. The release of [3H]taurine was compared to that of gamma-[3H]aminobutyric acid [( 3H]GABA) in cortical neurons and to that of D-[3H]aspartate in granule cells. Cortical neurons responded to potassium stimulation (1 min or continuously) by an immediate increase in [3H]GABA efflux of more than six times over the basal efflux, followed by a sharp decline despite the persistence of the stimulatory agent. The potassium-induced release of [3H]GABA was largely calcium-dependent. The release of [3H]taurine was considerably less in magnitude, only doubling after the stimulus, with a time course delayed in both onset and decline. The release of [3H]taurine was partially calcium-dependent and was also decreased in low-chloride solutions. In cerebellar granule cells, exposure to potassium resulted in a large (sixfold) and prompt release of D-[3H]aspartate, largely calcium-dependent. A totally different pattern was observed for the release of [3H]taurine. A stimulatory effect occurred only when cells were exposed continuously to potassium. Taurine efflux was very delayed, with a broad stimulus plateau reached after 15-20 min of stimulation. Taurine release was unaffected by omission of calcium, but it was abolished in a low-chloride medium. These results suggest that taurine is released from cells handling other neuroactive amino acids as neurotransmitters.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Biochemistry A, Panum Institute, University of Copehagen, Denmark.
A
A
Schousboe
H
H
Pasantes-Morales
D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D002478:Cells, Cultured; D002531:Cerebellum / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D005333:Fetus; D005971:Glutamates / Q000502:physiology*; D007700:Kinetics; D051379:Mice; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology*; D013654:Taurine / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism / Q000502:physiology*
D005971:Glutamates; D013654:Taurine; D001224:Aspartic Acid; D005680:gamma-Aminobutyric Acid; D011188:Potassium