DDT and Related Substances: Effects on Permeability Properties of Myelinated Xenopus Nerve Fibre. Potential Clamp Analysis

Abstract

An analysis was made of the effect of DDT and related substances on the membrane currents associated with step changes of the membrane potential. The substances tested are: DDT, DDD, DDE, DDMU, DDA, DDCN, bis‐(p‐chlorophenyl)‐acetamide and polychlormated bi‐phenyls (PCB). DDT. DDA and bis‐(p‐chlorophenyl)‐acetamide had acute effects on permeability parameters of the nerve membrane. The effects of the substances differed drastically from each other. DDT affected the turn off process of the sodium permeability mechanism after a positive potential step; the effect was large on fibres from Rana pipiens but negligible on fibres from Xenopus laeris. DDA affected the turn off process of the potassium permeability mechanism while bis‐“p‐chlorophenyl‘‐acetamide affected sodium and potassium permeability constants, Pxa and PK. The other substance; tested had no or only marginal acute effects. The main effect of DDA may be described as a specific effect on the rate constant βn. The obvious differences in effects of the substances on the permeability parameters were thus related to defined minute molecular differences of the studied substances.

Kinetics of veratridine action on Na channels of skeletal muscle.

“…Several other substances have effects similar to those of the alkaloid neurotoxins . DDT binds only to open channels, slows inactivation in such channels, and holds the channels open upon return to the resting potential 1968 ;Arhem and Frankenhaeuser, 1974 ;Dubois and Bergman, 1977 ;Lund and Narahashi, 1981 a;Leibowitz et al, 1986). Similar results have been obtained using a number of synthetic compounds that are only distantly related to DDT, such as 2,4,6trinitrophenol (Oxford and Pooler, 1975) and the pyrethroid insecticides (Lund and Narahashi, 1981b;Vijverberg et al, 1982Vijverberg et al, , 1983Leibowitz et al ., 1986).…”

Comparative study of the toxic actions of 2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane and 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene on the growth and respiratory activity of a microorganism used as a model

“…Since very similar partitionings of DDT and DDE have been estimated to occur in native and model membranes (7,34) and in bacterial lipid membranes (16), the differences in the toxic effects of these insecticides are not related to effective membrane concentrations. In other systems, DDE also exhibited lower toxicity than DDT (10,12,21,25). Therefore, we conclude that growth and respiration studies performed with our bacterial model, which reflects the lower toxicity of DDE compared to DDT, may be potentially useful as an alternative in vitro method for screening tests for chemical toxicity.…”

Sodium Channel Inactivation: Molecular Determinants and Modulation

“…Insect sodium channels are the target of many insecticides, especially dichlorodiphenyltrichloroethane (DDT) analogs and pyrethroids, synthetic analogs of the natural pyrethrin of Chrysanthemum flowers (311). These agents inhibit inactivation (346,467,524), but they also affect squid axons (262), lobster axons (312), as well as amphibian (14,112,178,469) and mammalian channels (141,142), however at higher concentrations and to a varying degree (155,310,418). Pyrethroids bind to a separate site allosterically coupled to sites 2 (345) and 3 (451).…”