ROLE OF PROTEIN PHOSPHATASE IN THE REGULATION OF NA-K+-ATPASE BY VASOPRESSIN IN THE CORTICAL COLLECTING DUCT()

In the cortical collecting duct (CCD), arginin vasopressin (AVP) has b een shown to increase the number and activity of basolateral Na+-K+-AT Pase by recruiting or activating a latent pool of pumps. However, the precise mechanism of this phenomenon is still unknown. The aim of this study was to investigate whether this AVP-induced increase in basolat eral Na+-K+- ATPase could depend on a dephosphorylation process. To th is purpose, the effect of protein serine/threonine phosphatase (PP) in hibitors was examined on both the specific H-3-ouabain binding (to eva luate the number of pumps in the basolateral membrane) and the ouabain -dependent Rb-86 uptake (to evaluate pump functionality) in the presen ce or absence of AVP. In addition, the activity of two PP, PP1 and PP2 A, was measured and the influence of AVP was examined on both enzymes. Experiments have been performed on mouse CCD isolated by microdissect ion. Results show that inhibition of PP2A prevents the AVP-induced inc rease in the number and activity of Na+-K+-ATPases, independent of an ef feet on the apical cell sodium entry. In addition, AVP rapidly incr eased the activity of PP2A without effect on PP1. These data suggest t hat PP2A is implied in the regulation of Na+-K+-ATPase activity by AVP in the CCD and that the AVP-dependent increase in the number of Na+-K +-ATPases is mediated by a PP2A-dependent dephosphorylation process.