Potent excitatory effects of a cardiotonic protein from the venom of the marine snail Conus magus on the guinea-pig left atria, vas deferens and ileum.

An active component (MAC) of Conus magus venom has been purified by gel filtration and ion exchange chromatographies, monitored by cardiotonic activity in the guinea-pig isolated left atria. MAC was estimated to be a protein of mol. wt between 45,000 and 65,000 by gel filtration and protease experiments. The purified protein at concentrations above 10(-7) g/ml elicited powerful rhythmic contractions of the guinea-pig vas deferens, rhythmic transient contractions of the ileum followed by relaxations, and a marked increase in the contractile force of the left atria. These responses to the toxin were abolished by tetrodotoxin. These results suggest that the action of MAC on the ileum and vas deferens may be mediated via nerves. It is also suggested that the major mechanism of action is due to activation of Na channels on the cell membrane.