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INHIBITION OF THE UPTAKE OF GABA AND RELATED AMINO ACIDS IN RAT BRAIN SLICES BY THE OPTICAL ISOMERS OF NIPECOTIC ACID
Author(s) -
Johnston G. A. R.,
KrogsgaardLarsen P.,
Stephanwn A. L.,
Twitchin B.
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.tb06488.x
Subject(s) - nipecotic acid , non competitive inhibition , chemistry , biochemistry , amino acid , kinetics , stereochemistry , enzyme , neurotransmitter , receptor , physics , quantum mechanics
— R(‐)‐Nipecotic acid was a more potent inhibitor than the S(+)‐isomer of the uptake of GABA, (+)‐nipecotic acid, and β‐alanine in rat brain slices. (‐)‐Nipecotic acid was an order of magnitude more potent as an inhibitor of GABA uptake than as an inhibitor of β‐alanine uptake, whereas the (+)‐isomer was less selective. (–)‐Nipecotic acid was a weak inhibitor of L‐proline uptake and of rat brain acetylcholinesterase activity. Kinetic studies showed that both isomers of nipecotic acid were competitive inhibitors of GABA uptake when added at the same time as GABA, but non‐competitive inhibitors when preincubated with the tissue for 15 min before addition of GABA. The apparent slope inhibition constants, which were not influenced by preincubation, indicated that (–)‐nipecotic acid has an affinity for the carrier some 5 times higher than that for (+)‐nipecotic acid. (–)‐Nipecotic acid stimulated the release of preloaded radioactive GABA from rat brain slices. These observations indicate that (–)‐nipecotic acid is a substrate‐competitive inhibitor of GABA which combines with the GABA carrier and is taken up. (−)‐Nipecotic acid and (+)‐2,4‐diaminobutyric acid, on the basis of their absolute structures and inhibition kinetics, are proposed to interact in a similar way with the GABA transport system.