Background. The effect of segment-speci®c proximal tubular injury on spatio-temporal osteopontin (OPN) distribution was determined in two different nephrotoxic rat models to evaluate its conceivability with a possible role for OPN in acute renal failure (ARF). OPN gene expression was further determined in proximal and distal tubular cells to investigate the origin of increased renal OPN. Methods. Renal OPN protein and mRNA expression were compared in the rat during mercuric-chloride-vs

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... n-induced ARF using immunohistochemistry and in situ hybridization. Results. Mercuric chloride primarily induced tubular injury and subsequent cell proliferation in proximal straight tubules (PST), whereas gentamicin predominantly injured proximal convoluted tubules (PCT). In both models, the distribution of OPN protein was associated with increased OPN mRNA levels in proximal as well as distal tubular cells. However, upregulation was delayed in the proximal tubular segment suffering most from injury, i.e. PCT in gentamicin ARF vs PST in mercuric-chloride ARF. OPN immunostaining at the apical cell membrane from distal tubules was in contrast to perinuclear vesicular staining in proximal tubular cells. Conclusions. OPN gene and protein expression is induced in both proximal and distal tubular cells during rat toxic ARF. The distinct subcellular localization in proximal vs distal tubular cells indicates differences in OPN processing anduor handling. The spatiotemporal distribution is consistent with a possible role in renal injury and regeneration.