Kinetic Data on the Inhibition of High‐affinity Choline Transport into Rat Forebrain Synaptosomes by Choline‐like Compounds and Nitrogen Mustard Analogues

Abstract

A series of choline analogues and nitrogen mustard derivatives were evaluated as inhibitors of high‐affinity transport of choline in rat forebrain synaptosomes. When synaptosomes were preincubated for 10 min with choline mustard aziridinium ion, monoethylcholine and monoethylcholine mustard aziridinium ion, the agents appeared to be equipotent as inhibitors of high‐affinity uptake (Ki=2.63, 3.15 and 2.72 μm, respectively). Acetylcholine mustard aziridinium ion was less potent than these compounds (Ki= 27.8 μm), but it was more potent than ethoxycholine and ethoxycholine mustard aziridinium ion (Ki= 500 and 403 μm) as a blocker of choline transport. From study with these compounds it was concluded that the high‐affinity choline transport mechanism shows specificity for hydroxylated compounds over those in which the same hydroxyl has been acetylated (10‐fold) and that the carbonyl oxygen of the acetylated analogues is important, as its removal (to form the ethylether derivative) decreased affinity another 20‐fold. The presence of an aziridinium ring on the quaternary nitrogen in place of two methyl groups did not affect the blocking of transport at 10 min of inhibitor preincubation and replacement of a methyl group on the nitrogen by an ethyl group did not alter affinity for the high‐affinity carrier. The aziridinium ring on the nitrogen of the mustard analogues was important, however, in determining the extent of reversibility of the binding of these agents to the carrier protein. Choline transport was not restored by washing synaptosomes that were incubated with choline mustard aziridinium ion or monoethylcholine mustard aziridinium ion, but was readily obtained in washed synaptosomes preincubated with monoethylcholine, hemicholinium‐3, or pyrrolcholine. The results indicate that the mustard analogues may be potent alkylators of the high‐affinity choline carrier and thus, useful agents in monitoring acetylcholine turnover in systems where the carrier is blocked.

Differences in control of descending inhibition in the proximal and distal regions of rat colon

“…One of its main effects is thought to be inhibition of the high affinity choline uptake system at the nerve terminals (Rylett & Colhoun, 1980;Mantione et al, 1981;Fisher et al, 1982;Curti & Marchbanks, 1984). There are few studies on the effect of AF64A on the peripheral nervous system (Mantione et al, 1983a;Allen, 1983;Hoyle et al, 1986).…”

Effects of physostigmine on AF64A-induced impairment of learning acquisition in rats.

“…It has been known that AF64A inhibits high-affinity choline transport (2,3). The compound also possesses inhibitory action toward the syn thesizing enzyme for acetylcholine (ACh), choline acetyltransferase (ChAT) (4), al though it does not influence [3H] QN B binding, a postsynaptic marker of the ACh system (5).…”

Pathways of decomposition of propylbenzilylcholine mustard in neutral and alkaline solution

“…The products of this scission may retain appreciable biological activity, but not at the same sites as the parent compounds. Acetylcholine mustard, for example, undergoes rapid hydrolysis at alkaline p H (Clement & Colhoun 1975a) and Colhoun and his collaborators have shown that the aziridinium ion analogue of choline so formed has long-lasting effects at cholinergic nerve terminals (Clement & Colhoun 1975a), which may result primarily from irreversible inhibition of choline transport (Clement & Colhoun 1975b;Rylett & Colhoun 1977, 1980. Reversible inhibition of choline acetyltransferase has also been observed (Rylett & Colhoun 1979).…”