FUNCTIONAL-MORPHOLOGY OF THE GLOMERULAR-FILTRATION BARRIER OF GALLUS-GALLUS

The anionic charge barrier and the endothelial and epithelial pore siz es on the glomerular filtration barrier (GFB) were examined in white l eghorn chickens (Gallus gallus). Ruthenium red was used to stain anion ic charge sites on the GFB. The tissue was treated by normal dehydrati on and freeze substitution dehydration for transmission electron micro scopy (TEM). In addition, the basal lamina was isolated for study. The results of our study indicate that G. gallus possess a thick, negativ ely charged glycocalyx surrounding the podocytes and slit diaphragm an d on the endothelium. However, in all cases, little anionic charge is present in the basal lamina. The pores on the endothelium are elliptic al and have mean dimensions of 148 x 110 nm. This is in contrast to ma mmals, which have smaller, round pores. The epithelial pores in G. gal lus measure approximately 35 nm in length, approximately 4 times large r than those found in mammals. These results indicate that the avian g lomerulus may allow the filtration of larger molecules from the plasma than occurs in mammals and that the charge on the molecule may not be as restrictive a filtration characteristic as in mammals. (C) 1996 Wi ley-Liss, Inc.