Differences in purity of commercial samples of hemicholinium-3: effects on high affinity choline uptake, neuromuscular transmission, acetylcholinesterase and carbachol and acetylcholine contractions.

Commercial samples of hemicholinium-3 (HC-3) have been found to vary in colour (from white to a sandy-yellow colour) and chemical composition. There were no significant differences between the various HC-3 samples with regards to inhibition of high affinity choline uptake into synaptosomes or inhibition of neuromuscular transmission in the chick biventer cervicis (CBC) preparation. Yellow HC-3 inhibited acetylcholinesterase more than white HC-3 with I₅₀ of 4.8 × 10^?5 M and 3.3 × 10^?4 M, respectively. Carbachol-induced contractions of the CBC preparation were inhibited more by yellow HC-3 than white HC-3; the opposite was true for acetylcholine- induced contractions. The results indicated that there is a minor contaminant in yellow HC-3 other than deanol which was a potent inhibitor of acetylcholinesterase and the carbachol response.