Evidence for calcium-dependent vesicular transmitter release insensitive to tetanus toxin and botulinum toxin type F.
Whether exocytosis evoked by a given releasing stimulus from different neuronal families or by different stimuli from one neuronal population occurs through identical mechanisms is unknown. We studied the release of [3H]noradrenaline, [3H]acetylcholine and [3H]dopamine induced by different stimuli from superfused rat brain synaptosomes pretreated with tetanus toxin or botulinum toxin F, known to block exocytosis by cleaving VAMP/synaptobrevin. The external Ca2(+)-dependent [3H]transmitter overflows evoked by KCl were similarly inhibited by tetanus toxin or botulinum toxin F; the toxins cleaved similar amounts of synaptosomal synaptobrevin, as determined by western blot analysis, suggesting prevalent involvement of synaptobrevin-II. GABA uptake-mediated release of the three [3H]transmitters was that differentially sensitive to the toxins: only the release of [3H]noradrenaline, which is dependent on external Ca2+, but not of [3H]acetylcholine and [3H]dopamine was blocked. Neither toxin affected the [3H]transmitter overflows evoked by the Ca2(+) ionophore ionomycin. Cadmium blocked the K(+)-evoked release of all [3H]transmitters and the GABA-evoked release of [3H]noradrenaline; the GABA-evoked releases of [3H]acetylcholine and [3H]dopamine and those elicited by ionomycin were insensitive to cadmium. The results suggest that tetanus toxin and botulinum toxin F selectively affect exocytosis linked to activation of voltage-sensitive Ca2(+) channels; the Ca2(+)-dependent, exocytotic-like release induced by stimuli not leading to activation of voltage-sensitive Ca2+ channels seems insensitive to these clostridial toxins.
Fassio
A
A
Dipartimento di Medicina Sperimentale, Università di Genova, Italy.
Sala
R
R
Bonanno
G
G
Marchi
M
M
Raiteri
M
M
D000818:Animals; D001905:Botulinum Toxins / Q000494:pharmacology*; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology; D002794:Choline / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism; D004351:Drug Resistance; D004594:Electrophysiology; D008297:Male; D008565:Membrane Proteins / Q000737:chemistry / Q000187:drug effects; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000378:metabolism; D050683:R-SNARE Proteins; D051381:Rats; D017207:Rats, Sprague-Dawley; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism*; D013744:Tetanus Toxin / Q000494:pharmacology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D015220:Calcium Channels; D008565:Membrane Proteins; D018377:Neurotransmitter Agents; D050683:R-SNARE Proteins; D013744:Tetanus Toxin; D005680:gamma-Aminobutyric Acid; D001905:Botulinum Toxins; D002794:Choline; D002118:Calcium; C096321:botulinum toxin type F; D004298:Dopamine; D009638:Norepinephrine