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CEREBRAL UPTAKES AND EXCHANGE DIFFUSION IN VITRO OF l ‐ AND d ‐GLUTAMATES
Author(s) -
Benjamin A. M.,
Quastel J. H.
Publication year - 1976
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1976.tb01493.x
Subject(s) - glutamate receptor , ouabain , incubation , biophysics , amino acid , biochemistry , chemistry , glutamic acid , in vitro , biology , receptor , sodium , organic chemistry
— 1. Whereas exogenous l ‐glutamate enters rat brain cortex slices incubated in a glucose‐physiological saline medium by both low affinity (K m = 0.7 m m ) and high affinity (K m = 27−30 μM) processes, the uptake of d ‐glutamate occurs only by a low affinity (K m = 2m m ) system. 2. d ‐glutamate appears to release l ‐glutamate from incubated rat brain cortex slices only to a very small extent, whether the tissue l ‐glutamate is of endogenous or exogenous origin. 3. Competitive inhibition takes place between l ‐ and d ‐glutamates at the low affinity carrier. This indicates that a common carrier exists for l ‐ and d ‐glutamates for the low affinity uptake process. 4. Apparently non‐competitive inhibition by d ‐glutamate of l ‐glutamate uptake occurs at the high affinity carrier, but the affinity of d ‐glutamate for this carrier is about 0.4% of that of l ‐glutamate. 5. Both d ‐, and l ‐glutamate exchange freely with labelled d ‐glutamate taken up by preliminary incubation of the brain slices with this amino acid. Whereas l ‐glutamate exchanges freely with labelled l ‐glutamate taken up by preliminary incubation, d ‐glutamate shows little or no exchange. 6. The uptake of labelled d ‐glutamate by exchange diffusion into brain slices previously loaded with unlabelled d ‐glutamate proceeds by a low affinity system. Therefore, the process of exchange diffusion does not necessarily involve a high affinity uptake component. 7. Whereas ouabain suppresses both high and low affinity concentrative uptakes of l ‐ and d ‐glutamate it has little apparent effect on the exchange diffusion process. 8. Sensitivity to tetrodotoxin of evoked release of l ‐ and d ‐glutamates, taken up by brain slices by preliminary incubation with these amino acids, indicates that the major proportion of the uptake of exogenous l ‐ or d ‐glutamate proceeds into non‐neuronal structures (presumably the glia). 9. At 0°C non‐carrier mediated (passive) diffusion of labelled d ‐ and l ‐glutamate takes place in brain slices.