engleski

Cadmium impairs the integrity of rat renal brush border membrane vesicles (BBMV) in vitro

Long-term exposure of humans and experimental animals to cadmium (Cd) leads to impaired reabsorption of fluids and solutes in proximal tubule (PT) cells. Ultrastructural studies of the kidney tissue from Cd-treated rats showed a marked shortening and focal loss of brush-border microvilli in PT cells (Condron et al. : J. Submicrosc. Cytol. Pathol. 26(1):51-58, 1994), thus indicating that the loss of reabsorptive surface due to damaged integrity of brush-border membrane (BBM) may contribute to the functional defects in this toxic condition. The reason for the damage and loss of BBM in Cd-nephrotoxicity is not clear. We have studied an in vitro effect of Cd upon the integrity of isolated rat renal coritcal BBM vesicles using the potassium diffusion potential-driven intravesicular acidification as an indicator. Generation of transmembrane pH gradients was monitored by the acridine orange fluorescence quench method. In preliminary experiments we demonstrated that the degree of fluorescence quenching (transmembrane pH) was proportional to the amount of closed vesicles. Following preincubation of the fixed amount of BBM vesicles with Cd in vitro, we found that: a) the vesicles integrity decreased with increasing concentrations (10-500 uM) of Cd, and b) the loss of closed vesicles was high at 37C, intermediate at 25°C, and low at 0C. The integrity of BBM vesicles was also strongly damaged following preincubation at 37°C with Hg, Pb, Zn and Cu, whereas Al. La and Fe weakly damaged the vesicles. The integrity of BBM vesicles was not significantly affected by Mg, Mn and Ba. We conclude that: a) Cd and various other heavy metals may directly damage the integrity of BBM and cause shortening and loss of microvilli in PT cells, and b) due to sensitivity of the BBM vesicle integrity to low concentrations of heavy metals, great caution should be taken in experiments in which in vitro effects of heavy metals upon various transports are studied in isolated membrane vesicles. In such cases, an impaired transport may result from the loss of vesicle integrity and not necessarily from the sepcific inhibition of the transporter.

nephrotoxicity; cadmium; brush border vesicles; membrane integrity

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