UPTAKE AND METABOLISM OF GLUTAMATE BY ISOLATED TOAD BRAINS CONTAINING DIFFERENT LEVELS OF ENDOGENOUS AMINO ACIDS

Autor: Claude F. Baxter, R. P. Shank
Rok vydání: 1975
Předmět:
Zdroj: Journal of Neurochemistry. 24:641-646
ISSN: 1471-4159
0022-3042
DOI: 10.1111/j.1471-4159.1975.tb03841.x
Popis: —The uptake of [U-14C]glutamate into the amphibian brain was studied in vitro using brains from toads (Bufo boreas) adapted either to a fresh water (FWA) or an hyperosmotic saline (HOA) environment. Initial rates of 14C-glutamate uptake showed a single apparent Km of about 0·2 mm. Uptake by HOA brains was slower than that by FWA brains, reflecting perhaps a non-competitive type of inhibition by the higher content of glutamate in the HOA brains. Although the glutamate content of HOA brains was maintained during prolonged incubation at twice the level found in FWA toads, other metabolic parameters measured in the two types of brain preparations were surprisingly similar. Tissue to medium concentration ratios of greater than 3000:1 were generated by both FWA and HOA brains. In both brain systems the clearance of glutamate from the medium was accompanied by a rapid conversion of the amino acid to glutamine and its release into the medium. In both the FWA and HOA toad brain systems some [U-14C]glutamate was metabolized to aspartate and GABA; in both systems the specific radioactivity (SA) of glutamine in the tissue was from two to four times greater than that of glutamate; also the SA of glutamine released into the medium was higher by several orders of magnitude than the SA of glutamine in brain tissues. These and other findings support the concept that, in both the FWA and HOA toad brains, transport processes are instrumental in preserving low extracellular levels of glutamate but that mechanisms other than transport are responsible for the maintenance of different levels of glutamate in the FWA and HOA toad brains.
Databáze: OpenAIRE
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