DEXTRAN SULFATE BINDING TO ISOLATED RAT GLOMERULI AND GLOMERULAR-BASEMENT-MEMBRANE

The binding of dextran sulfate to isolated glomeruli and glomerular basement membrane has been studied and compared to the glomerular uptake of dextran sulfate during isolated kidney perfusion. Two binding sites for [H-3]dextran sulfate to isolated glomeruli could be identified at 37 degrees C; an high affinity site (K-A = 4.76.10(6) M(-1)) (4.4.10(10) molecules/glomerulus) and a low affinity site (K-A = 5.8.10(4) M(-1)) (2.0.10(11) molecules/glomerulus) whereas at 4 degrees C there was only an high affinity binding site (K-A = 1.43.10(6) M(-1)) (7.10(10) molecules/glomerulus). The glomerular binding of dextran sulfate appears to be to cellular elements as the binding sites were not present in purified glomerular basement membrane which effectively did not bind dextran sulfate. The binding of dextran sulfate to isolated glomeruli was far in excess of that found associated with glomerular uptake during isolated kidney perfusion. The difference has been discussed in terms of the different capillary wall surfaces exposed to the dextran sulfate and the concentration gradients that may exist in the two types of experiments. The structural integrity of the glomerulus is also important in governing the amount of binding as structural disintegration through freeze-thawing and sonication revealed more binding sites. These data may suggest a specific distribution of binding sites and specific transglomerular transport pathways where many of these sites are not exposed. The nature of binding [H-3]dextran sulfate to isolated glomeruli was different to isolated perfused kidney glomerular uptake when studied in terms of the kinetics of exchange with unlabelled dextran sulfate. This exchange data suggests a passive binding mechanism in isolated glomeruli whereas in isolated kidney perfusion the nature of the exchange would suggest a glomerular intracellular uptake (Tay, M., et al. (1991) Am. J. Physiol. 260, F549-F554).