GABAB-receptor-mediated inhibition of calcium signals in isolated nerve terminals.
Time-resolved fluorometric monitoring of rapid changes in intracellular Ca(2+)-concentrations [Ca2+]i was employed to analyze the effect of gamma-aminobutyric acid (GABA) on evoked Ca(2+)-signals in rat hippocampal synaptosomes. The inhibitory action of GABA was mimicked by Baclofen, the selective agonist for GABAB-receptors, and also by the nonhydrolyzable GTP-derivative GTP-gamma-S. Preincubation of synaptosomes with GABA or baclofen for up to 250 ms before depolarization resulted in a maximal inhibition. The GABA-induced attenuation of the evoked rise in [Ca2+]i was maximal during the first milliseconds after depolarization. The inhibitory action of GABA apparently does not involve second messengers, such as cAMP or IP3/DAG; the GABA-induced inhibition of presynaptic voltage-dependent Ca(2+)-channels may be mediated directly by G-proteins.
Tareilus
E
E
University Stuttgart-Hohenheim, Institute of Zoophysiology, Germany.
Schoch
J
J
Breer
H
H
D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects* / Q000648:ultrastructure; D066298:In Vitro Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D018080:Receptors, GABA-B / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects*; D013574:Synaptosomes / Q000187:drug effects*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D018080:Receptors, GABA-B; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D005680:gamma-Aminobutyric Acid; D001418:Baclofen; D002118:Calcium