Influence of charge on filtration across renal basement membrane films in vitro.

The filtration of differently charged species of myoglobin and dextran across films of isolated basement membrane in vitro showed that the filtration behavior of both polymers was influenced by charge. Rejection increased with increasing negative charge. Titration of the isolated basement membrane revealed an isoionic point of pH 5.5 and an isoelectric point of pH 5.7. The net negative charge at pH 7.4 was 0.15 mEq/g protein; this charge was attributed to carboxylate anion. Glycosaminoglycan sulphate did not contribute significantly to the net charge. Filtration of narrow range dextran fractions across films of basement membrane at the isoelectric point markedly reduced differences in filtration due to charge confirming that the differences in behavior found at pH 7.4 were due to charge interactions between the solutes and the membranes. Physical characterization of the charged and uncharged dextran fractions revealed no substantial differences in size or shape for the differently charged species.