Effect of gossypol on erythrocyte membrane function: specific inhibition of inorganic anion exchange and interaction with band 3.

The effects of gossypol on membrane functions of the human erythrocyte were studied. Gossypol (10 microM) had no effect on spontaneous hemolysis, osmotic fragility, cell volume, cholinesterase activity, hexose transport, ouabain-sensitive inorganic cation transport, ouabain-insensitive inorganic cation transport and nucleoside transport. Conversely, 10 microM gossypol inhibited inorganic anion transport by approximately 90% for three different substrates, i.e., phosphate, sulfate and chloride. Inhibition of inorganic anion transport was specific as 10 microM gossypol had no effect on the eight aforementioned membrane-related functions of the human erythrocyte. Inhibition inorganic anion transport was characterized using sulfate as the substrate and had the following features: it was potent, with a Ki of approximately 3 microM; it was rapid, with onset occurring in less than 1 min; it was potently blocked by physiological concentrations of albumin and plasma with 50% blocking achieved at 0.03% (w/v) albumin; it occurred by a noncompetitive kinetic mechanism; it was independent of medium Ca++, Mg++ or pH. Gossypol was bound to human erythrocytes and cell membranes isolated from erythrocytes. 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid is a potent inhibitor of anion transport and can be covalently bound to band 3. Covalently bound 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid blocked a fraction of gossypol binding to erythrocyte membranes.(ABSTRACT TRUNCATED AT 250 WORDS)