Increased synthesis and AVP unresponsiveness of Na,K-ATPase in collecting duct from nephrotic rats

Renal sodium retention is responsible for ascites and edema in nephrotic sy ndrome. In puromycin aminonucleoside (PAN)-induced nephrosis, sodium retent ion originates in part from the collecting duct, and it is associated with increased Na,K-ATPase activity in the cortical collecting duct (CCD). The a ims of this study were to evaluate whether the outer medullary collecting d uct (OMCD) also participates to sodium retention and to determine the mecha nisms responsible for stimulation of Na,K-ATPase in CCD. PAN nephrosis incr eased Na,K-ATPase activity in the CCD but not in OMCD. The two-fold increas e of Na,K-ATPase activity in CCD was associated with two-fold increases in the number of alpha and beta Na,K-ATPase subunits mRNA determined by quanti tative RT-PCR and of the total amount of Na,K-ATPase alpha subunits estimat ed by Western blotting. PAN nephrosis also increased two-fold the amount of Na,K-ATPase alpha subunit at the basolateral membrane of CCD principal cel ls, as determined by Western blotting after biotinylation and streptavidin precipitation and by immunofluorescence. The intracellular pool of latent N a,K-ATPase units also increased in size and was no longer recruitable by va sopressin and cAMP. This unresponsiveness of the intracellular pool of Na,K -ATPase to vasopressin was not the result of any alteration of the molecula r and functional expression of the vasopressin V-2 receptor/adenylyl cyclas e (AC) complex. It is concluded that PAN nephrosis (1) does not alter sodiu m reabsorption in OMCD, (2) is associated with increased synthesis and memb rane expression of Na,K-ATPase in the CCD, and (3) alters the normal traffi cking of intracellular Na,K-ATPase units to the basolateral membrane.