The sea anemone toxin Bc2 induces continuous or transient exocytosis, in the presence of sustained levels of high cytosolic Ca2+ in chromaffin cells.
We have isolated and characterized a new excitatory toxin from the venom of the sea anemone Bunodosoma caissarum, named Bc2. We investigated the mechanism of action of the toxin on Ca(2+)-regulated exocytosis in single bovine adrenal chromaffin cells, monitoring simultaneously fura-2 fluorescence measurements and electrochemical recordings using a carbon fiber microelectrode. Bc2 induced quantal release of catecholamines in a calcium-dependent manner. This release was associated with a sustained rise in cytosolic Ca(2+) and displayed two different patterns of response: a continuous discharge of prolonged duration that changed to a transient burst as the toxin concentration (or incubation time) increased. Continuous secretion was dependent on the activity of native voltage-dependent Ca(2+) channels and showed a pattern similar to that of alpha-latrotoxin; however, its kinetics adjusted better to that of continuous cell depolarization with high K(+) concentration. In contrast, transient secretion was independent of Ca(2+) entry through native voltage-dependent Ca(2+) channels and showed inhibition of late vesicle fusion that was accompanied by "freezing" of F-actin disassembly. These new features make Bc2 a promising new tool for studying the machinery of neurotransmitter release.
Ales
E
E
Instituto de Farmacologia Teófilo Hernando, Departamento de Farmacologia, Facultad de Medicina, Universidad Autónoma de Madrid, C/Arzobispo Morcillo 4, 28029 Madrid, Spain. eva.ales@uam.es
Gabilan
N H
NH
Cano-Abad
M F
MF
Garcia
A G
AG
Lopez
M G
MG
D000313:Adrenal Medulla / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002417:Cattle; D019439:Chromaffin Cells / Q000187:drug effects* / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism*; D005089:Exocytosis / Q000187:drug effects*; D007700:Kinetics; D008387:Marine Toxins / Q000494:pharmacology*; D008561:Membrane Fusion; D011188:Potassium / Q000378:metabolism; D012615:Sea Anemones
D008387:Marine Toxins; D011188:Potassium; D002118:Calcium