PHARMACOLOGY OF ANATOXIN-A, PRODUCED BY THE FRESHWATER CYANOPHYTE ANABAENA-FLOS-AQUAE NRC-44-1

Anatoxin-a (ANTX-A) is the neuromuscular blocking agent produced by the freshwater cyanophyte Anabaena flos-aquae (Lyngb.) de Bréb. strain NRC-44-1. Its pharmacological properties have been investigated and compared with that of synthetic ANTX-A which was derived from l-cocaine. ANTX-A is a potent depolarizing neuromuscular blocking agent possessing both muscarinic and nicotinic activity. Responses to ANTX-A on the isolated frog-rectus abdominus muscle were qualitatively similar to those obtained with acetylcholine, carbachol and decamethonium, with ANTX-A being the most potent. Neostigmine and tetrodotoxin failed to affect responses to ANTX-A. The affinity constant for ANTX-A on the frog-rectus preparation was 3·1 μM, compared to 1·0 μM for carbachol. On the chick biventer cervicis preparation ANTX-A was less potent but produced responses similar to that of decamethonium. d-Tubocurarine and hexamethonium caused a shift to the right in the dose-response curves of ANTX-A and decamethonium. On the isolated rat phrenic nerve-hemidiaphragm ANTX-A and decamethonium blocked the muscle twitch response which was not reversed by neostigmine. ANTX-A produced a depolarizing blockade on the cat sciatic nerve-anterior tibialis preparation which was similar but less than that produced by decamethonium. On the isolated guinea pig ileum, ANTX-A had a potency approximately the same as that of 1,1-dimethyl-4-phenyl piperazinium but less than that of acetylcholine. © 1979.