Transcytosis of Retinol-Binding Protein across Renal Proximal Tubule Cells after Megalin (gp 330)-Mediated Endocytosis

摘要: Abstract . Plasma retinol-binding protein (RBP) combined with vitamin A (retinol) is partially filtered through the glomerulus and then absorbed by proximal tubule cells, leading to recycling of retinol circulation. Recently, it was shown that reabsorption RBP-retinol complexes cells mediated megalin (gp 330), an apical endocytic receptor. It proposed RBP transported lysosomes, where degraded, thus liberating retinol, which combines newly synthesized be secreted into bloodstream. This study shows passage immortalized rat renal (IRPT) occurs transcytosis after megalin-mediated endocytosis, provides alternative pathway for retinol. IRPT cultured as polarized monolayers tight junctions were used on permeable filters in upper chamber dual-chambered devices, expression exclusively surface. After addition incubation at 37°C, intact found fluids collected from lower chamber. In contrast, control substances (mannitol, lysozyme, albumin, glutathione-S-transferase) not appreciably across indicating paracellular leakage. Confocal microscopy analysis revealed RBP-containing granules membrane, subapically, also basolateral membranes. When added together competitors, amount transcytosed markedly reduced. We some internalized degraded but this process affected endocytosed lysosomes rather cells.