Albumin uptake in OK cells exposed to rotenone: a model for studying the effects of mitochondrial dysfunction on endocytosis in the proximal tubule?
BACKGROUND
The renal proximal tubule (PT) is clinically vulnerable to mitochondrial dysfunction; sub-lethal injury can lead to the Fanconi syndrome, with elevated urinary excretion of low-molecular-weight proteins. As the mechanism that couples mitochondrial dysfunction to impaired PT low-molecular weight protein uptake is unknown, we investigated the effect of respiratory chain (RC) inhibitors on endocytosis of FITC-albumin in PT-derived OK cells.


METHODS
Uptake of FITC-albumin was quantified using confocal microscopy. Cytosolic ATP levels were measured in real time using both luciferin/luciferase assays and measurements of free [Mg(2+)]. Reactive oxygen species production was measured using mitosox.


RESULTS
RC blockade produced only a small decrease in cytosolic ATP levels and had minimal effect on FITC-albumin uptake. Inhibition of glycolysis caused a much bigger decrease in both cytosolic ATP levels and FITC-albumin endocytosis. Rotenone led to higher rates of reactive oxygen species production than other RC inhibitors. Rotenone also caused widespread structural damage on electron microscopy, which was mimicked by colchicine and prevented by taxol; consistent with inhibition of microtubule polymerisation as the underlying mechanism.


CONCLUSIONS
Endocytosis of FITC-albumin is ATP-dependent in OK cells, but the cells are very glycolytic and therefore represent a poor metabolic model of the PT. Rotenone has toxic extra-mitochondrial structural effects.
Hall
A M
AM
Centre for Nephrology, University of London, London , UK. andrew.hall@ucl.ac.uk
Campanella
M
M
Loesch
A
A
Duchen
M R
MR
Unwin
R J
RJ
D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000818:Animals; D002461:Cell Line, Transformed; D002470:Cell Survival; D003078:Colchicine / Q000633:toxicity; D003486:Cyanides / Q000633:toxicity; D003911:Dextrans / Q000378:metabolism; D004579:Electron Transport / Q000187:drug effects / Q000502:physiology; D004705:Endocytosis; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism; D005198:Fanconi Syndrome / Q000378:metabolism; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives* / Q000378:metabolism; D006019:Glycolysis / Q000187:drug effects; D007687:Kidney Tubules, Proximal / Q000166:cytology*; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D009893:Opossums; D017239:Paclitaxel / Q000494:pharmacology; D011725:Pyridines / Q000633:toxicity; D017382:Reactive Oxygen Species / Q000378:metabolism; D012402:Rotenone / Q000494:pharmacology / Q000633:toxicity*; D012709:Serum Albumin / Q000378:metabolism*
D003486:Cyanides; D003911:Dextrans; C518288:FITC-albumin; D011725:Pyridines; D017382:Reactive Oxygen Species; D012709:Serum Albumin; C015219:fluorescein isothiocyanate dextran; D012402:Rotenone; D000255:Adenosine Triphosphate; D016650:Fluorescein-5-isothiocyanate; D017239:Paclitaxel; D003078:Colchicine