Actions of Ptychodiscus brevis red tide toxin on metabolic and transmitter-releasing properties of synaptosomes.

A pure toxin isolated from Ptychodiscus brevis stimulated differential release of amino acid neurotransmitters from mammalian cortical synaptosomes together with loss of K+ content and respiratory stimulation at 40 ng/ml. The effect was blocked by tetrodotoxin and by verapamil, implicating Na+ channel activation and possibly Ca2+ influx as necessary for the response, although the response did not change upon omission of Ca2+. Verapamil was therefore likely to be acting as a Na+ channel blocker in this instance. The toxin at 40 ng/ml caused acetylcholine release from guinea pig ileum, which is consistent with the proposed depolarising action for the toxin.