The Sea Anemone Toxin Bc2 Induces Continuous or Transient Exocytosis, in the Presence of Sustained Levels of High Cytosolic Ca2+ in Chromaffin Cells

• Published in: The Journal of biological chemistry 2000-12, Vol.275 (48), p.37488-37495
• Main Authors: Alés, Eva, Gabilan, Nelson H., Cano-Abad, Marı́a F., Garcı́a, Antonio G., López, Manuela G.
• Format: Article
• Language: English
• Subjects: Adrenal Medulla - cytology; Adrenal Medulla - drug effects; Adrenal Medulla - metabolism; Animals; Calcium - metabolism; Calcium Signaling; Cattle; Chromaffin Cells - drug effects; Chromaffin Cells - metabolism; Cytosol - metabolism; Exocytosis - drug effects; Kinetics; Marine Toxins - pharmacology; Membrane Fusion; Potassium - metabolism; Sea Anemones
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M007388200

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 Ca2+-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 Ca2+ 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 Ca2+channels and showed a pattern similar to that of α-latrotoxin; however, its kinetics adjusted better to that of continuous cell depolarization with high K+ concentration. In contrast, transient secretion was independent of Ca2+ entry through native voltage-dependent Ca2+ 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.