Anatoxin-a-evoked [3H]dopamine release from rat striatal synaptosomes.
Presynaptic nicotinic acetylcholine receptors on striatal nerve terminals modulate the release of dopamine. Using rat striatal synaptosomes loaded with [3H]dopamine, we have characterized the action of the selective nicotinic agonist, (+/-)anatoxin-a, with respect to [3H]dopamine release, in order to explore the mechanisms coupling nicotinic receptor activation to exocytosis. Anatoxin-a evoked [3H]dopamine release in a concentration-dependent and mecamylamine-sensitive manner, EC50 = 0.11 microM. The maximum [3H]dopamine release elicited by anatoxin-a was only 20% of the maximum elicited by KCl depolarization; there was no additivity between anatoxin-a and sub-maximal concentrations of KCl. Both agents stimulated Ca(2+)-dependent release that was equally sensitive to inhibition by 200 microM Cd2+. This result suggests that anatoxin-a-stimulated exocytosis is mediated by Ca2+ influx via voltage-sensitive Ca2+ channels, with little contribution from Ca2+ entering directly through the nicotinic receptor channel. This view is supported by the abolition of anatoxin-a-evoked [3H]dopamine release in Na(+)-depleted medium. A partial (40%) inhibition by tetrodotoxin was observed. These data suggest that activation of presynaptic nicotinic acetylcholine receptors by anatoxin-a results in an influx of Na+, producing sufficient local depolarization to open voltage-sensitive Ca2+ and Na+ channels. The latter may then amplify the response, activating further Ca2+ channels. The particular voltage-sensitive Ca2+ channels involved remain to be determined.
Soliakov
L
L
School of Biology and Biochemistry, University of Bath, UK.
Gallagher
T
T
Wonnacott
S
S
D000818:Animals; D001427:Bacterial Toxins / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D003342:Corpus Striatum / Q000187:drug effects / Q000502:physiology*; D000458:Cyanobacteria; D000087522:Cyanobacteria Toxins; D004298:Dopamine / Q000378:metabolism / Q000502:physiology*; D007473:Ion Channels / Q000187:drug effects; D008297:Male; D008387:Marine Toxins / Q000494:pharmacology*; D052998:Microcystins; D018722:Nicotinic Agonists / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013574:Synaptosomes / Q000187:drug effects / Q000502:physiology*; D014326:Tropanes
D001427:Bacterial Toxins; D000087522:Cyanobacteria Toxins; D007473:Ion Channels; D008387:Marine Toxins; D052998:Microcystins; D018722:Nicotinic Agonists; D014326:Tropanes; C509783:anatoxin a; D002118:Calcium; D004298:Dopamine