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Specific labeling of the basolateral cell membrane along the rat nephron with an immunopurified antibody

In order to produce polyclonal antibodies that could be used in morphological and functional studies of the mammalian kidney collecting duct, endocytic vesicles in the rat kidney papillary duct cells were loaded with the fluorescein marker (FITC-dextran) in vivo, isolated by differential and Percoll density gradient centrifugation, enzymatically characterized, and used to immunize rabbits. The immune serum labeled 6 different protein bands by immunoblotting in brush-border (BBM) and basolateral membranes (BLM) isolated from the rat kidney cortex homogenate. One of the labeled protein bands (Mr120 kDa; p120) was strongy enriched in the BLM. By indirect immuno-fluorescence cytochemistry in 4 m thick cryosections of the fixed kidney tissue, the immune serum intensely stained the proximal tubule cell BBM, whereas the BLM of the same cells was weakly stained. Using the BLM p120 band as a template, we immunoadsorbed from the immune serum an antibody that strongy labeled the same protein band in the BLM and weakly labeled a 50 kDa protein band in BBM and BLM by immunoblotting, whereas by immunofluorescence cytochemistry, the antibody exclusively stained the BLM of various cells along the rat nephron. The observed pattern of staining with the anti-p120 antibody resembled that with the monoclonal antibody to the Na/K-ATPase1 subunit. However, the identity of p120 with the Na/K-ATPase 1 subunit was excluded by finding that a) the anti-1 subunit antibody did not label the p120 in the BLM, and b) the immunoadsorbed antibody to p120 did not label the purified 1 subunit of the Na/K-ATPase. The identity of p120 remains to be established. The respective antibody could be used to study morphological changes of the BLM in cells along the nephron in various (patho)physiological states

immunopurification; basolateral membrane; nephron; rat

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