The integrity of renal cortical brush-border and basolateral membrane vesicles is damaged in vitro by nephrotoxic heavy metals.
Poisoning of experimental animals with cadmium (Cd), mercury (Hg), lead (Pb) or cis-diamminedichloroplatinum (cis-Pt) causes shortening and focal loss of microvilli in proximal tubule (PT) cells, thus indicating that the reduced reabsorptive surface due to damaged integrity of brush-border membrane (BBM) may contribute to the reabsorptive and secretory defects in these toxic states. In addition, in in vitro studies with isolated renal cortical BBM vesicles (BBMV), heavy metals (HM) inhibit transport of various compounds, and these data were interpreted as being a result of a direct inhibition of the respective membrane transporters. In this work we used a DeltapH-driven acridine orange fluorescence quench assay to test if various divalent cations affect in vitro the integrity of BBMV and basolateral membrane vesicles (BLMV) isolated from the rat renal cortex. In Cd-treated BBMV we found that: (a) the integrity of vesicles decreased with increasing concentrations of Cd; and (b) the loss of sealed vesicles was high at 37 degrees C, intermediate at 25 degrees C, and very low at 0 degrees C. The loss of sealed BBMV was caused also by Hg, Cu, Pb and Zn (Hg>>>Cu=Cd>Pb=Zn). Cis-Pt, Al, Fe, Ba, Mg and Mn had no effect. BLMV were damaged by HM with an efficiency Hg>>>Cd=Pb=Cu, whereas other divalent cations, including Zn, were ineffective. An SH-group protector, dithiothreitol, prevented the loss of sealed vesicles in some (Hg, Pb, Cu) but not in all (Cd, Zn) cases. We conclude that the nephrotoxic HM directly damage the integrity of PT cell plasma membranes; this may cause shortening and loss of microvilli and basolateral invaginations in HM-treated experimental animals in vivo. The data also indicate that caution should be taken when effects of HM on various transports are studied in isolated membrane vesicles in vitro; an impaired transport may result from the loss of vesicle integrity, and not necessarily from the direct inhibition of a transporter.
Herak-Kramberger
C M
CM
The Unit of Molecular Toxicology, Institute for Medical Research and Occupational Health, Ksaverska cesta 2, HR-10001 Zagreb, Croatia.
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D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism; D002478:Cells, Cultured; D022162:Cytoplasmic Vesicles / Q000187:drug effects* / Q000378:metabolism; D004229:Dithiothreitol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005470:Fluorometry; D007672:Kidney Cortex / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D019216:Metals, Heavy / Q000633:toxicity*; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
D019216:Metals, Heavy; D004229:Dithiothreitol