Effect of ionic contents in saline on depolarizing afterpotential induced by phenothrin and methoxychlor

1. The depolarizing afterpotential induced by phenothrin and methoxychlor in crayfish giant axons was measured intracellularly. 2. Changes in the K+ ion concentration did not affect the depolarizing afterpotential when evaluated as the membrane potential. 3. Addition of tetrodotoxin or replacement of the Cl- ions by OAc- ions or of the Na+ ions by choline ions reduced the depolarizing afterpotential and the action potential. 4. A ratio of the reduction of the depolarizing afterpotential in saline that contained OAc- ions to that of the action potential was similar to that measured in the saline containing tetrodotoxin. 5. With the increase in the choline concentration, the relative value of the depolarizing afterpotential to that measured before the replacement decreased almost linearly with that of the decrease in the action potential.