HIGH GLOMERULAR-PERMEABILITY OF BIKUNIN DESPITE SIMILARITY IN CHARGE AND HYDRODYNAMIC SIZE TO SERUM-ALBUMIN

Bikunin is a chondroitin-sulphate containing serum protein with a Stok es-Einstein radius and a negative net charge close to those of serum a lbumin. The plasma half life of bikunin is about 10 minutes, and appro ximately half of its clearance occurs in the kidneys. The quantitative role of glomerular filtration in the renal clearance of this protein has not been determined. To assess the glomerular permeability of biku nin we used isolated rat kidneys that were perfused with an albumin so lution. The metabolic activities of the tubuli were inhibited by low t emperature (8 degrees C). The clearances of radiolabeled bikunin and a lbumin were repeatedly determined under identical conditions. The frac tional clearance of bikunin was found to be SO times higher than that of albumin: 15% +/- 1% versus 0.18% +/- 0.02%. This value for bikunin can fully account for its renal clearance in vivo. It has previously b een shown that uncharged flexible solutes, such as dextrans, have high er renal clearances than globular molecules with similar radii. The hi gh glomerular permeability of bikunin is therefore probably due to its elongated and flexible configuration. Moreover, the observed clearanc e value of the anionic molecule bikunin is close to that of a neutral flexible dextran of similar size, indicating that the charge of bikuni n is of little importance for its glomerular permeability.