Actions of β‐Bungarotoxin on Amino Acid Transmitter Release

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Abstract
The actions of purified β‐bungarotoxin (5 or 10 μg/ml) on the metabolic and transmitter‐releasing properties of rat cortical synaptosomes was studied. The toxin stimulated control respiratory rates, but prevented the respiratory response to veratrine. Tissue potassium levels were greatly reduced (54%) and endogenous glutamate, aspartate and GABA showed increased levels of release (10‐ to 25‐fold), but other amino acids were unaffected or showed much smaller changes. Tissue levels of these amino acids were reduced in proportion. The toxin inhibited the uptake of [U‐14C]GABA (35%) and [U‐14C]glutamate (53%) over 5‐min incubation periods. This uptake‐inhibition was Ca2+‐dependent and was reduced by tetrodotoxin. Miniature‐end‐plate‐potential (m.e.p. p.) frequencies at the locust neuromuscular junction (extensor tibialis) were greatly (four‐ to sevenfold) accelerated by local application of the toxin (5 μg/ml). This effect was reversible and occupied about 20 min. Amplitudes of m.e.p. p.'s were also increased and muscle membrane depolarization occurred. The results are interpreted as being due to a depolarizing action of the toxin.
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