Penetration of an organphosphorus compound into squid axon and its effects on metabolism and function.

The tertiary analogute of phospholine, namely, (C(2)H(5)O)(2)P(O)SCH(2)CH(2)N(CH(3))(2), is a potent, irreversible inhibitor of cholinesterase which, when externally applied to the sqluid giant axon, readily penetrates in its inhibitory form into the axoplasm. However, even a 10(-2) molar solution of this compound does not block axonal conduction unless the axon is first treated with a low concentration of venom from the cottonmouth moccasin. The question of the activity of acetylcholinesterase in these axons is considered, and the possibility of subcellular permeability barriers for indivisual components of the excitable membrane is discussed.