Formation of aqueous pores in the human erythrocyte membrane after oxidative cross-linking of spectrin by diamide.

Oxidation of erythrocyte membrane SH-groups by diamide and tetrathionate induces cross-linking of spectrin (Haest, C.W.M., Kamp, D., Plasa, G. and Deuticke, B. (1977) Biochim. Biophys. Acta 469, 226-230). This cross-linking was now shown to go along with a concentration- and time-dependent enhancement of membrane permeability for hydrophilic nonelectrolytes and ions. The enhancement is specific for oxidative SH-group modifications, is reversible by reduction of the induced disulfides, can be suppressed by a very brief pre-treatment of the cells with low concentrations of N-ethylmaleimide and is strongly temperature-dependent. The pathway of the induced permeability discriminates nonelectrolytes on the basis of molecular size and exhibits a very low activation energy (Ea 3-8 kcal/mol). These findings are reconcilable with the formation of a somewhat inhomogeneous population of aqueous pores with radii probably less than or equal to 0.65 nm. Estimated pore numbers vary with the size of the probe molecule. Assuming a diffusion coefficient as in bulk water within the pore, at least 20 pores per cell have to be postulated; more realistic lower diffusion coefficients increase that number. Alterations of the lipid domain by changes of cholesterol contents and insertion of hexanol or nonionic detergents alter the number or size of the pores. Since aggregation of skeletal and intrinsic membrane proteins also occurs after the SH-oxidation, in parallel to the formation of membrane leaks, one may consider (a) defects in the disturbed bilayer interface, (b) a mismatch between lipid and intrinsic proteins or (c) channels in between aggregated intrinsic proteins as structures forming the pores induced by diamide treatment.