The structural specificity of choline transport into cholinergic nerve terminals

The accumulation of choline, homocholine, and 4-hydroxybutyltrimethylammonium by rat brain synaptosomes was measured; the choline uptake mechanism transported homocholine but not hydroxybutyltrimethylammonium, which, in addition, did not block choline accumulation. In cats' superior cervical ganglia, preganglionic nerve stimulation increased the accumulation of homocholine, but not that of hydroxybutyltrimethylammonium. It is concluded that the substrate specificity of the choline transport mechanism is such that increasing the N--O atom distance by one methylene group retains affinity, but increasing this distance by two methylene groups does not.