Abstract
A cyclic choline analogue, 3-hydroxy-N,N-dimethylpiperidinium, has been shown to be transported into a crude preparation of synaptosomes by high and low affinity transport mechanisms. Under conditions favouring the high affinity system the synaptosomes metabolized approximately 50% of the accumulated analogue to 3-acetoxy-N,N-dimethylpiperidinium, which was detected by paper electrophoresis. The phrenic nerve endplate region of a mouse hemidiaphragm accumulated 3-hydroxy-N,N-dimethylpiperidinium on nervous stimulation. This tissue metabolized approximately 60% of the accumulated analogue to the acetylated derivative which was released on nervous stimulation into the bathing medium. Compared to acetylcholine, 3-acetoxy-N,N-dimethylpiperidinium was shown to be 57 times less potent an agonist at the nicotinic receptors of the frog rectus abdominis muscle and 162 times less potent an agonist at the muscarinic receptors of the guinea-pig ileum. It is concluded that 3-hydroxy-N,N-dimethylpiperidinium is a precursor of a false cholinergic transmitter.