title: Stimulation of [3H] GABA and beta-[3H] alanine release from rat brain slices by cis-4-aminocrotonic acid.
abstract: cis-4-Aminocrotonic acid (CACA; 100 microM), an analogue of GABA in a folded conformation, stimulated the passive release of [3H] GABA from slices of rat cerebellum, cerebral cortex, retina, and spinal cord and of beta-[3H]alanine from slices of cerebellum and spinal cord without influencing potassium-evoked release. In contrast, CACA (100 microM) did not stimulate the passive release of [3H]taurine from slices of cerebellum and spinal cord or of D-[3H]aspartate from slices of cerebellum and did not influence potassium-evoked release of [3H]-taurine from the cerebellum and spinal cord and D-[3H]-aspartate from the cerebellum. These results suggest that the effects of CACA on GABA and beta-alanine release are due to CACA acting as a substrate for a beta-alanine-sensitive GABA transport system, consistent with CACA inhibiting the uptake of beta-[3H]alanine into slices of rat cerebellum and cerebral cortex. The observed Ki for CACA against beta-[3H]alanine uptake in the cerebellum was 750 +/- 60 microM. CACA appears to be 10-fold weaker as a substrate for the transporter system than as an agonist for the GABAc receptor. The effects of CACA on GABA and beta-alanine release provide indirect evidence for a GABA transporter in cerebellum, cerebral cortex, retina, and spinal cord that transports GABA, beta-alanine, CACA, and nipecotic acid that has a similar pharmacological profile to that of the GABA transporter, GAT-3, cloned from rat CNS. The structural similarities of GABA, beta-alanine, CACA, and nipecotic acid are demonstrated by computer-aided molecular modeling, providing information on the possible conformations of these substances being transported by a common carrier protein.
authors.affiliation: Department of Pharmacology, University of Sydney, New South Wales, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Chebib
authors.forename: G A
authors.initials: GA
authors.lastname: Johnston
mesh_terms: D000409:Alanine / Q000493:pharmacokinetics*; D000818:Animals; D001224:Aspartic Acid / Q000493:pharmacokinetics; D001692:Biological Transport / Q000187:drug effects; D015415:Biomarkers; D002352:Carrier Proteins / Q000378:metabolism; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D003437:Crotonates / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D018682:GABA Agents / Q000494:pharmacology; D005973:Glutamine / Q000378:metabolism; D008297:Male; D009557:Nipecotic Acids / Q000494:pharmacology; D009924:Organ Culture Techniques; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000187:drug effects / Q000378:metabolism; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism; D013654:Taurine / Q000493:pharmacokinetics; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000493:pharmacokinetics*
chemical_list: D015415:Biomarkers; D002352:Carrier Proteins; D003437:Crotonates; D018682:GABA Agents; D009557:Nipecotic Acids; D005973:Glutamine; D014316:Tritium; D013654:Taurine; C055331:4-aminocrotonic acid; D001224:Aspartic Acid; D005680:gamma-Aminobutyric Acid; D011189:Potassium Chloride; C045598:N-(4,4-diphenyl-3-butenyl)nipecotic acid; D000409:Alanine