Binding to saxitoxin to electrically excitable neuroblastoma cells

Area of Science:

• Neuroscience
• Molecular Pharmacology
• Cell Biology

Background:

• Neuroblastoma cells exhibit electrical excitability.
• Action potential sodium ionophores are critical for neuronal function.
• Saxitoxin is a known blocker of sodium channels.

Purpose of the Study:

• To investigate the specific binding of saxitoxin to neuroblastoma cells.
• To characterize the binding sites and stoichiometry of saxitoxin interaction.
• To determine the relationship between saxitoxin binding and sodium ionophore activity.

Main Methods:

• Inhibition assays to determine the inhibitory constant (KI) of saxitoxin.
• Radioligand binding experiments to quantify binding sites (KD) and capacity.
• Competitive binding assays using tetrodotoxin, scorpion toxin, and batrachotoxin.
• Comparison of binding in excitable and non-excitable neuroblastoma clones.

Main Results:

• Saxitoxin inhibited action potential sodium ionophores with a KI of 3.7 nM.
• A single class of saturable binding sites was detected (KD = 3.9 nM, capacity = 156 fmol/mg).
• Binding was specifically inhibited by tetrodotoxin and absent in non-excitable N103 clone.

Conclusions:

• Saxitoxin binds specifically to the action potential sodium ionophore in neuroblastoma cells.
• The stoichiometry suggests three saxitoxin receptor sites per scorpion toxin receptor site.
• These findings provide insights into the molecular structure and function of sodium ionophores.