REVERSED POLARITY OF NA+-K+-ATPASE - MISLOCATION TO APICAL PLASMA-MEMBRANES IN POLYCYSTIC KIDNEY-DISEASE EPITHELIA

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder in which renal tubules become enormously enlarged due to fluid accumulation. Na+-K+-ATPase was compared in normal and cystic regions of whole kidneys and in confluent primary cultures of microdissected renal tubule and cyst-lining epithelia. Immunostaining with antibodies directed against the Na+-K+-ATPase catalytic alpha-subunit was confined to apical, luminal plasma membranes of ADPKD epithelia, which was a complete reversal of the normal renal tubule polarized location in basolateral membranes. Mislocated Na+-K+-ATPase was shown to be functionally active, because identical intense apical staining was observed by use of a cytochemical assay. In addition, biochemical assays showed a significant increase in these ouabain-inhibitable Na+-K+-ATPase specific activity levels in ADPKD kidneys compared with large-matched normal kidneys. Specific binding of [H-3]ouabain was not only increased but also confined to the apical membrane vesicles prepared from cystic regions of ADPKD kidneys compared with normal age-matched controls, in which binding was confined to basolateral membrane vesicles. Although steady-state levels of Na+-K+-ATPase alpha- and beta-subunit in mRNAs were increased somewhat in ADPKD kidneys, this alone was not sufficient to account for the observed activiation. Confluent ADPKD epithelia grown on dual-chamber, permeable membrane supports also showed reversed polarity of (NaCl)-Na-22 vectorial transport, because this was from basal to apical media compartments. Because this transport could also be blocked by ouabain, this suggested apical Na+-K+-ATPase was responsible and implicated altered polarity of Na+-K+-ATPase and resultant Na+ secretion as a mechanism for cyst formation in ADPKD. Because no reversal of polarity of other basolateral or apical membrane proteins was detected, and intracellular sorting defect specific for Na+-K+-ATPase is proposed.