Uptake and intracellular distribution of ferritin in the rat distal convoluted tubule

Uptake and intracellular distribution of ferritin in the rat distal convoluted tubule. The purpose of this study was to determine the uptake and intracellular distribution of anionic ferritin (AF) and cationic ferritin (CF) in the distal convoluted tubule (DCT) of the rat kidney. Male Sprague-Dawley rats were prepared for micropuncture, and individual distal tubules were perfused with 5 or 10 mg/ml of AF or 0.1 or 0.5 mg/ml of CF in isotonic saline for either 30sec or 3min. The tubules were fixed by perfusion with 6.25% glutaraldehyde either immediately or at different time intervals after exposure to ferritin. Electron microscopy of tubules fixed immediately after perfusion showed no binding of AF to the apical cell membrane, and only traces of AF were observed in small apical structures. In contrast, CF was extensively bound to the apical cell membrane and located in apical vesicles and tubules, and in multivesicular bodies. Occasionally, CF was observed in Golgi vesicles and cisternae. Sixtymin after perfusion with ferritin, traces of AF were present in multivesicular bodies and lysosome-like structures. Thirty and 60min after perfusion, large concentrations of CF were located in multivesicular bodies and lysosome-like bodies. This study reveals that in the DCT, CF is bound to the apical cell membrane and taken up into the tubule cells, whereas only traces of AF are taken up, indicating that the charge of a protein molecule may determine whether or not the protein is reabsorbed by the DCT. The demonstration of CF in the Golgi complex is compatible with the existence of membrane recycling in cells of the DCT. Captation et distribution intracellulaire de la ferritine dans le tube contourne distal du rat. Notre etude a ete fit de determiner la captation et la distribution intracellulaire de la ferritine anionique (AF) et de la ferritine cationique (CF) dans le tube contourne distal (DCT) du rein de rat. Des rats mâles Sprague-Dawley ont ete prepares pour des experiences de microponction et des tubes distaux individuels ont ete perfuses avec 5 ou 10 mg/ml de l'AF ou 0,1 ou 0,5 mg/ml de la CF dans du solute sale isotonique pendant 30sec ou 3 mn. Les tubules ont ete fixes par perfusion au moyen de glutaraldehyde a 6,25% soit immediatement, soit a divers intervalles de temps apres l'exposition a la ferritine. La microscopie electronique des tubules fixes immediatement apres perfusion n'a pas montre de liaison de AF a la membrane cellulaire apicale et seules quelques traces de AF ont ete detectees dans les petites structures apicales. Au contraire, CF est liee de facon importante a la membrane cellulaire apicale et localisee dans les vesicules et les tubules apicaux et dans les corps multivesiculaires. De facon in constante CF a ete observee dans les vesicules et les citernes de Golgi. Soixante minutes apres la perfusion de ferritine des traces d'AF etaient encore detectees dans les corps multivesiculaires et les structures semblables aux lysosomes. Trente et 60min apres la perfusion, des concentrations importantes de CF ont ete detectees dans les corps multivesiculaires et dans les corps semblables a des lysosomes. Notre etude revele que dans le DCT CF est liee a la membrane cellulaire apicale et captee a l'interieur des cellules, alors que seules des traces d'AF sont captees, ce qui indique que la charge d'une molecule proteique peut etre un facteur qui determine sa reabsorption par le DCT. La description de CF dans l'appareil de Golgi est compatible avec l'existence d'un recyclage membranaire dans les cellules du DCT.