Two acceptor sub-types for dendrotoxin in chick synaptic membranes distinguishable by beta-bungarotoxin

Area of Science:

• Neuroscience
• Molecular Biology
• Pharmacology

Background:

• Dendrotoxin from Dendroaspis angusticeps facilitates neurotransmitter release by inhibiting brain A-current K+ channels.
• Understanding the molecular targets of neurotoxins is crucial for elucidating synaptic function.

Purpose of the Study:

• To characterize the proteinaceous acceptors for dendrotoxin in chick synaptic membranes.
• To investigate the interaction of dendrotoxin and related toxins with these acceptors.

Main Methods:

• Equilibrium and kinetic binding measurements using radioiodinated dendrotoxin.
• Competition binding assays with beta-bungarotoxin and other toxins.
• Toxin cross-linking, SDS-PAGE, and Western blot analysis.

Main Results:

• Two distinct populations of membrane acceptors for dendrotoxin were identified, with high (Kd ~0.5 nM) and low (Kd ~15 nM) affinities.
• The high-affinity acceptor specifically bound beta-bungarotoxin, a homologous neurotoxin.
• Cross-linking studies revealed acceptor components of 75,000 and 69,000 Mr, derived from both acceptor species.

Conclusions:

• Chick synaptic membranes possess at least two types of dendrotoxin acceptors with differential affinities.
• A shared acceptor exists for dendrotoxin and beta-bungarotoxin, alongside a dendrotoxin-selective subtype.
• These findings provide a molecular basis for the opposing effects of these toxins on neurotransmitter release.