Ion selectivity of aqueous leaks induced in the erythrocyte membrane by crosslinking of membrane proteins.

The aqueous leak induced in the human erythrocyte membrane by crosslinking of spectrin via disulfide bridges formed in the presence of diamide (Deuticke, B., Poser, B., Lütkemeier, P. and Haest, C.W.M. (1983) Biochim. Biophys. Acta 731, 196-210) was further characterized with respect to its ion selectivity by means of (a) measurements of cell volume changes or hemolysis, (b) determination of membrane potentials and (c) analysis of potential-driven ion fluxes. The leak turned out to be slightly cation-selective (PK:PCl approximately equal to 4:1). It discriminates mono- from divalent ions (PNa:PMg greater than 100:1, PCl:PSO4 greater than 10:1) and to a much lesser extent monovalent ions among each other. The selectivities for monovalent ions follow the sequence of free solution mobilities, increasing in the order Li+ less than or equal to Na+ less than K+ less than or equal to Rb+ less than Cs+ and F- less than Cl- less than Br- less than I-. Polyatomic anions also fit into that order. Quantitatively, the ratios of permeabilities of the leak are larger than those of the ion mobilities in free solution. The ion permeability of the leak is concentration-independent up to at least 150 mM. The ion milieu, however, has marked effects on leak permeability, most pronounced for chaotropic ions (guanidinium, nitrate, thiocyanate), which increase leak fluxes of charged and uncharged solutes. The results support the view that, besides geometric constraints, weak coulombic or dipolar interactions between penetrating ions and structural elements of the leak determine permselectivity.