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

Abstract

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 ␣-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.

Modulatory Mechanism of the Endogenous Peptide Catestatin on Neuronal Nicotinic Acetylcholine Receptors and Exocytosis

“…9A). This kinetic pattern is similar to that obtained after continuous depolarization of single bovine chromaffin cells with a high [K ϩ ] solution (Gil et al, 1998;Alés et al, 2000). Although the first phase most likely reflects fusion and release of readily releasable vesicles that require only an elevation of [Ca 2ϩ ] c for exocytosis (Thomas et al, 1993;Xu et al, 1998), the second phase probably represents vesicles that need lower [Ca 2ϩ ] c levels to undergo priming and maturation before they are ready for fusion (Xu et al, 1998).…”

Plasma Albumin Induces Cytosolic Calcium Oscilations and DNA Synthesis in Human Cultured Astrocytes

“…Madrid, Spain), diluted at 1 : 100 was used onto fixed cells [27] to identify astrocytes and anti-NeuN (Chemicon International. Madrid, Spain), diluted at 1 : 100, was used to identify neurons.…”

Glycerotoxin stimulates neurotransmitter release from N‐type Ca2+ channel expressing neurons

“…Finally, the sea anemone Bc2 neurotoxin has been shown to stimulate glutamate release from synaptosomes (Migues et al . 1999) and catecholamine secretion from chromaffin cells (Ales et al . 2000) via a yet to be identified mechanism.…”

“…2000) via a yet to be identified mechanism. It is conceivable that like equinotoxin II, Bc2 also exhibits pore‐forming activity (Ales et al . 2000; Meunier et al .…”