CA2-DEPENDENT AND NA+-DEPENDENT DEPOLARIZATION-INDUCED BY MAITOTOXIN IN THE CRAYFISH GIANT-AXON()

1. Maitotoxin (MTX) depolarized the membrane of the crayfish giant axo n and decreased the amplitude and maximum rate of rise of action poten tials in an irreversible manner 2. The depolarizing action of MTX was attenuated in low Ca (1 mM; 1/10 of normal concentration) solution and was also inhibited by 2 mM Co2+, 300 muM Ni2+, 1 muM nifedipine, 10 m uM verapamil or 1 muM tetrodotoxin. 3. These results suggest that the depolarization by MTX in the crayfish giant axon may be related to cha nges not only in Ca permeability but also in Na permeability, possibly through the modification of existing Na or Ca channels and/or a new t ype of channel or pore induced by MTX.