Interaction of toxic cations with the glomerulus: Binding of Ni to purified glomerular basement membrane

Abstract

Basement membrane was prepared from the glomeruli of bovine kidneys using either detergent extraction, sonication or trichloroacetic acid (TCA) treatment. An assay was developed to measure the binding of radiolabelled metal salts to particulate suspensions of the membrane. 63Ni bound to the anionic glycosaminoglycan (GAG) sites of the membrane. This binding could be blocked by the cationic dye ruthenium red, and was sensitive to treatment with heparitinase but not to mild collagenase digestion. At pH 7.4 at low ionic strength (5 mM TrisHCl), a high affinity ( K a = 4.5 × 10 6 M −1) binding site was distinguished. It was insensitive to increasing salt concentration, but was abolished by desulfation of the basement membrane preparation. 54Mn showed a similar binding pattern to Ni, while 65Zn and 109Cd lacked the high affinity site. In all cases the bulk of binding was of lower affinity and was of a non-specific electrostatic nature. Most, but not all, was abolished by salt concentrations comparable to those of the plasma filtrate (140 mM NaCl). These results are discussed in the context of sensitivity of the glomerular charge barrier to toxic divalent ions.