Ionic Channels and Nerve Membrane Lipoproteins: DDT-Nerve Membrane Interaction

Abstract

DDT inhibits the potassium current and delays the turning off process of the sodium current in voltage-clamped axons. In order to identify the target sites of DDT in nerve membranes, experiments were performed so as to investigate (i) the accumulation of ¹⁴C DDT in nerve fiber plasma membranes of the squid Dosidicus gigas and (ii) the interaction of DDT with isolated nerve membranes, their lipid constituents and membrane proteins. Two nerve membrane fractions were used: fraction I tentatively identified as the axolemma, and fraction II as the plasma membranes of the satellite cells, including Schwann cells. The interaction of DDT with human high density lipoprotein (HDL) and lipid-free apolipoprotein (apo-HDL), was also investigated. The monolayer technique and the spectrophotofluorometric method were used. The results show that DDT accumulates in the plasma membranes of the nerve fibers. They also indicate that DDT causes a reduction in the fluorescence intensity of the protein aromatic residues which is only observed when the protein is bound to lipids. The lipoprotein structures of nerve cell membranes and HDL facilitate the interaction of DDT. The identification of the nerve membrane components which are the targets of DDT may be useful to obtain knowledge of the chemical structure of the axolemma ionic channels.