Proximal tubule role in albumin homeostasis: controversy, species differences, and the contributions of intravital microscopy

Albuminuria is a known risk factor for the development and progression of chronic kidney disease. Glomerular disease has been shown to result in increased glomerular permeability and albuminuria, but the role of the proximal tubule (PT) in albumin homeostasis under physiologic and disease conditions remains controversial. The controversy centers around the glomerular sieving coefficient of albumin (GSCa), the percentage of albumin filtered across the glomerulus, and the ability of the PT to reabsorb and transcytose the reabsorbed albumin across the basolateral membrane for reuse (reclamation). Direct visualization and quantification of the GSCa does not agree with previous studies where the role of the PT was felt to be minimal. Thus, the dogma was urinary albumin equaled glomerular filtration of albumin. Tubular handling of filtered albuminKidney InternationalVol. 104Issue 6PreviewAlbumin is the most abundant circulating protein in the plasma, playing key roles in maintaining colloid pressure, transporting multiple endogenous and exogenous ligands, and contributing to antioxidant processes.1 Albumin is produced by hepatocytes and delivered into the bloodstream through interaction with the neonatal crystallizable fragment receptor (FcRn).23 The catabolism of albumin occurs mostly in the endothelial cells of the muscle, skin, and liver, as well as in the proximal tubule cells of the kidney. Full-Text PDF