Acetylcholinesterase and ATPase activities in erythrocyte ghosts are not affected by 1,2,4-trichlorobenzene: Implications for toxicity by narcotic chemicals

The membrane concentration at which 1,2,4-trichlorobenzene (1,2,4- triCBz) affects the functioning of diverse membrane proteins and the partition coefficient of 1,2,4-triCBz between ghosts and water were studied. Earlier studies showed that the fluidity of phospholipids is increased at concentrations of 20 to 60 mmol/kg lipid and that lethality by narcosis in an organism occurs at concentrations of 40 to 160 mmol/kg lipid, irrespective of the physicochemical properties of the nonpolar narcotic chemical. Concentrations in a horse erythrocyte membrane of 110 to 1,100 mmol/kg lipid did not affect the activity of the Na+/K+ATPase and Mg2+ATPase. Acetylcholinesterase functioning was not disturbed at membrane concentrations of 33 to 330 mmol/kg lipid. Therefore, disturbance of the membrane proteins studied is not the mechanism by which narcotic chemicals act. The functioning of these membrane proteins is not affected by the change in phospholipid fluidity that is known to occur in organisms that die due to exposure to narcotic chemicals. In vitro bioassays often contain a high concentration of lipids in the system. With hydrophobic test compounds, the concentration of the test compound in the exposure medium at the start of the experiment is much higher than the exposure concentration at equilibrium. Therefore, effects in in vitro bioassays should not be expressed in terms of the exposure concentration at the start of the experiment.