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 redu ced reabsorptive surface due to damaged integrity of brush-border membrane (BBM) may contribute to thr reabsorptive and secretory defects in these tox ic states. In addition, in in vitro studies with isolated renal cortical BB M 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 Delta pH-dr iven acridine orange fluorescence quench assay to test if various divalent cations affect in vitro the integrity of BBMV and basolateral membrane vesi cles (BLMV) isolated from the rat renal cortex. In Cd-treated BBMV Lye foun d that: (a) the integrity of vesicles decreased with increasing concentrati ons of Cd; and (b) the loss of sealed vesicles was high at 37 degreesC, int ermediate at 25 degreesC, and very low at 0 degreesC. The loss of sealed BB MV was caused also by Hg, Cn, Pb and Zn (Hg Cu = Cd > Pb = Zn). Cis-Pt, Al, Fe, Pa, Mg and Mn had no effect. BLMV were damaged by I-IM with an efficie ncy Hg Cd = Pb = Cu, whereas other divalent cations, including Zn, were ine ffective. An SH-group protector, dithiothreitol, prevented the loss of seal ed 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 me mbranes; this may cause shortening and loss of microvilli and basolateral i nvaginations in HM-treated experimental animals in vivo. The data also indi cate that caution should be taken when effects of HM on various transports are studied in isolated membrane vesicles in vitro; an impaired transport m ay result from the loss of vesicle integrity, and not necessarily from the direct inhibition of a transporter. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.