An octopus toxin, maculotoxin, selectively blocks sodium current in squid axons

Area of Science:

• Neuroscience
• Pharmacology
• Marine Biology

Background:

• The posterior salivary glands of the octopus Hapalochlaena maculosa produce a potent neurotoxin.
• Understanding neurotoxin mechanisms is crucial for neuroscience and drug development.

Purpose of the Study:

• To characterize the biophysical and chemical properties of maculotoxin (MTX).
• To elucidate the specific effects of MTX on neuronal ion currents.

Main Methods:

• Isolation and purification of maculotoxin (MTX) from octopus salivary glands.
• Voltage-clamp experiments on squid giant axons to measure ion currents.
• Systematic variation of pH, electrical stimulation patterns, and ion concentrations.

Main Results:

• Maculotoxin (MTX) is a low molecular weight, stable, cationic neurotoxin that selectively blocks sodium current without affecting potassium current.
• MTX effectiveness is enhanced by repetitive depolarizing pulses and is dependent on a cationic form (optimal at pH 7-1).
• MTX slows the activation kinetics of sodium conductance, particularly with small depolarizations, but does not affect inactivation or gating currents.

Conclusions:

• Maculotoxin (MTX) acts as a specific blocker of voltage-gated sodium channels.
• The toxin's mechanism involves interaction with the sodium channel's gating properties.
• MTX's stability and specific action make it a valuable tool for studying sodium channel function.