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NHE3 is targeted to the basolateral plasma membrane in straight proximal tubule segments of colchicine-treated rats

The structural and functional polarity of epithelial cells is maintained by vesicle-mediated and microtubule (MT)-dependent trafficking of various components between the cell membrane and intracellular organelles. In colchicine (C)-treated rats, depolymerization of MT in renal proximal tubule cells (PTC) causes disruption of vesicle trafficking and recycling, and redistribution of some brush-border membrane (BBM) proteins into cytoplasmic vesicles. We recently showed that following MT depolymerization in rats, the BBM aquaporin-1 (AQP1), a protein common to cells of convoluted (CPT) and straight (SPT) PT segments, was translocated from the BBM into intracellular vesicles in the CPT but not in the SPT (Eur. J. Physiol. 439:321, 2000). To further document these segmental differences, we studied the effect of MT loss on the distribution of BBM sodium-proton exchanger (NHE3) by immunofluorescence in tissue sections and by immunobloting in BBM isolated from C-treated rats (3.2 mg/kg, i.p., a single dose 12h before sacrifice). In control rats, NHE3 in the CPT was labeled strongly in the BBM and weakly in subapical endosomes, whereas in the SPT, NHE3 was present in the BBM and in numerous, randomly scattered cytoplasmic vesicles. In the CPT of C-treated rats, a dramatic redistribution of the antigen from the BBM into intracellular vesicles, and a loss of the respective 80 kDa protein band in isolated cortical BBM, occured. In the SPT, however, the abundance of NHE3 in the BBM was not visibly changed. The NHE3-positive intracellular vesicles vanished, and the antigen was clearly detectable in the basolateral plasma membrane (BLM). These data suggest that recycling of NHE3 in the SPT may include MT-independent targeting to the BLM, followed by the MT-dependent, vesicle-mediated transcytosis to the BBM.

colchicine; sodium-proton exchanger; microtubules; vesicle trafficking

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