engleski

Loss of microtubules and impaired endocytosis in proximal tubule cells in cadmium-intoxicated rats

LOSS OF MICROTUBULES AND IMPAIRED ENDOCYTOSIS IN PROXIMAL TUBULE CELLS IN CADMIUM-INTOXICATED RATS Ivan Sabolic, Carol M. Herak-Kramberger, & Dennis Brown, IMI, Zagreb, Croatia & MGH, Boston, MA, USA Chronic cadmium (Cd) intoxication in man and experimental animals is manifested by defects in reabsorptive and secretory functions of the renal proximal tubule (PT). Proteinuria is an early sign of Cd nephrotoxicity. In the healthy kidney, a bulk of filtered proteins is reabsorbed by endocytosis (EN) in the PT cells, where EN and exocytosis represent parts of the microtubule -dependent vesicle trafficking mechanism that recycle membrane components between the plasma membrane and intracellular organelles. An impaired vesicle recycling due to microtubule derangement may inhibit EN and cause proteinuria. We studied microtubules and EN in the PT cells in control and CdCl2-treated (2 mg Cd/kg B.W., s.c., daily for 14 days) rats. Using the monoclonal anti-a-tubulin antibody, the immunofluorescence studies showed brightly stained bundle-like arrangements of PT cell microtubules in frozen sections of fixed control kidneys. In tissues from Cd-treated rats, the staining was weak and the arrangement of microtubules was irregular. However, the Western blot data showed much higher content of a-tubulin in tissue homogenates from Cd-intoxicated rats, thus indicating that the majority of microtubules in cells intoxicated with Cd had been depolymerized. To test the cell EN, rats were injected in vivo with the fluorescein isothiocyanate-dextran (FITC-dextran, 35 mg/rat, i.v.), a fluid phase marker that is filtered and endocytosed by the PT cells. As observed histochemically in control tissue sections, endosomes in PT cells concentrated in the cell subapical region and exhibited a strong uptake of FITC-dextran. In PT cells of Cd-intoxicated rats, the endosomal uptake of the fluorescent marker was strongly diminished and vesicles were randomly scattered in the cytoplasm. Conslusion: In PT cells of Cd-intoxicated rats, microtubules are largely depolymerized and EN is strongly inhibited. Proteinuria in Cd-intoxicated rats may result from diminished EN of the filtered proteins. The data indicate that the vesicle trafficking via endo- and exocytosis may be impaired in Cd-nephrotoxicity.

endocytosis; microtubules; cadmium; kidney; rat

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