Membrane damage in human erythrocytes caused by captan and captafol

Treatment of human erythrocytes with 5 × 10^-5 M captan or captafol caused a rapid increase in the efflux of intracellular potassium. Captafol had a more pronounced effect than captan on cation permeability. Captafol also decreased anion permeability whereas captan did not affect this process. Glutathione (5 × 10^-4 M) had little effect in reducing potassium efflux when added to the cells after they were incubated for 1 h with captan or captafol, but it was effective in reducing the potassium loss when added to the cells prior to their treatment with the fungicides. Captafol caused an increase in osmotic fragility of the cells. Incubation of the cell membranes with captafol resulted in the liberation of a small fraction of membrane phospholipids, whereas captan produced no effect. Both the fungicides readily reacted with the sulfhydryl groups in the isolated membrane; 31.5 and 45.7% of the membrane sulfhydryl groups had disappeared following treatment with captan and captafol, respectively. It is suggested that the reaction of captan or captafol and/or their reaction products with the sulfhydryl and amino groups of the red cell membrane protein produces changes in the structure of the membrane with consequent alteration in its permeability.