In colchicine-treated rats, cellular distribution of AQP-1 in convoluted and straight proximal tubule segments is differently affected.

In cells along the nephron, the recycling of various components between the plasma membrane and intracellular organelles by vesicle trafficking depends on intact microtubules (MT). Previous studies of rats treated with the MT-disrupting drug colchicine showed that some brush-border membrane (BBM) transporters in renal proximal convoluted tubule cells (PCTC) become internalized in numerous vesicles randomly scattered in the cytoplasm. In this study, we compare the intracellular distribution of MT and several BBM proteins [megalin, vacuolar (V)-ATPase, water channel aquaporin-1 (AQP-1)] as well as endocytosis of the in-vivo-injected fluorescent marker FITC-dextran in PCTC and proximal straight tubule cells (PSTC) in control and colchicine-treated rats. Immunoblotting and immunocytochemical data show that in the PCTC and PSTC colchicine treatment causes: (1) disappearance of MT, (2) strongly diminished endocytosis of FITC-dextran, and (3) marked loss of megalin and V-ATPase from the BBM and their redistribution into intracellular vesicles. Similar pattern was observed for the distribution of AQP-1 in the PCTC. However, in the PSTC, the staining intensity of AQP-1 in the BBM, as well as its intracellular distribution remained unaffected by colchicine treatment. We conclude that in the PSTC, either MT play a minor role in the recycling of AQP-1 between the BBM and intracellular vesicles or BBM AQP-1 turns over much more slowly than in the PCTC.