STRUCTURE AND PROPERTIES OF THE GLOMERULAR FILTRATION BARRIER OF VERTEBRATES: ROLE OF CHARGE FOR FILTERING PROTEINS

Abstract

The renal glomerulus is a unique structure that distinguishes the nephrons of vertebrates from the nephridia of invertebrate animals, providing a direct connection between the circulatory and excretory systems and the most effective control of the composition of the internal environment due to the significant intensification of filtration. The modern ideas about the structure of the glomerular filtration barrier in representatives of all major groups of vertebrates (cyclostomes, fishes, amphibians, reptiles and birds, mammals) were reviewed. Emphasis is placed on the role of the charge of the glomerular barrier structures for its selective properties; approaches to studying the contribution of the anionic components of the renal filter to preventing the loss of plasma proteins are described. The main models of the glomerular filter functioning presented in the literature are considered. Negative charge has been demonstrated to be a distinctive feature of the glomerular filter in all vertebrates. It was shown that a multiple increase of the glomerular filtration rate (from lower vertebrates to birds and mammals) was accompanied by a number of structural changes that ensured the passage of a significant volume of water and dissolved low-molecular substances through the glomerular filter: an increase in the number and ordering of fenestrae in the endothelium of glomerular capillaries, thinning of the glomerular basement membrane and complete exclusion of cellular elements from it. It has been shown that comparative physiological data on the glomerular filter in different groups of vertebrates most strongly confirm the electrokinetic model of the glomerular filtration, since it explains the importance of the evolutionarily conservative structure of podocytes and the role of a set of fixed anionic charges in the filter wall to prevent the loss of macromolecules (primarily proteins) from blood at different intensities of the ultrafiltration.