Comparison of the Action of an Organophosphorus Insecticide and Its Metabolite on Chloride and Sulfate Transport in Erythrocyte Membrane

Abstract

The effect of the organophosphorus insecticide methylparathion and its main metabolite methylparaoxon on chloride and sulfate equilibrium exchange in pig erythrocytes was investigated using an isotope labelling technique. Efflux of both radioactive isotopes with time followed a single exponential. Methylparathion and methylparaoxon inhibited the chloride equilibrium exchange in erythrocyte ghosts in a dose- and time-dependent manner. There was no difference between effects evoked by these two compounds. Methylparathion and methylparaoxon inhibited sulfate efflux from resealed ghosts. The effect was also dose- and time-dependent. Again, there was no difference between the action of both agents. Dixon analysis revealed a non-competitive character of the inhibition of the exchange of both anions with apparent Ki values 183 and 184 microM for methylparathion and methylparaoxon, respectively in the case of chloride transport; for sulfate exchange these values were 675 and 648 microM. It was suggested that structural similarity between the parent agent and its metabolite accounts for their identical effects. Methylparathion and methylparaoxon might inhibit the anion exchange indirectly by changing the fluidity of the erythrocyte membrane or directly by binding to the band 3 protein and evoking conformational changes that lead to the inhibition of the anion transport. The insecticides, due to their ability to phosphorylate, might also disturb some regulation processes in the band 3 protein and affect anion transport in this way.