Alterations of acetylcholine and choline metabolism in mammalian preparations treated with beta-bungarotoxin

We have studied the effects of beta-bungarotoxin on acetylcholine and choline metabolism in central and peripheral cholinergic preparations using a gas chromatographic-mass spectrometric assay for acetylcholine and choline. In contrast with previous reports, beta-Bungarotoxin did not inhibit the high-affinity uptake of labeled choline or the synthesis of acetylcholine in rat brain synaptosomal fractions. However, the toxin did cause a significant increase of medium choline when it was incubated with synaptosomal fractions. This increase of endogenous choline in the medium may account for the previously reported inhibition of choline uptake because of a dilution of the specific activity of the labeled choline in the medium. Several experiments are reported in which a further characterization was made of the effect of beta-bungarotoxin on medium choline. beta-Bungarotoxin was also shown to cause a large increase of acetylcholine release from rat brain minces and a depletion of the acetylcholine content of minces. A similar phenomenon was found in diaphragm preparations that were exposed continuously to beta-bungarotoxin. However, diaphragms that were treated for only 30 min with toxin showed the previously reported increase of acetylcholine content. beta-bungarotoxin did not have any measurable effect on acetylcholine turnover in smooth muscle preparations from guinea pig ileum. These results help to explain certain inconsistencies in the literature regarding the action of beta-bungarotoxin.