Protein phosphatase-1 in the kidney: evidence for a role in the regulation of medullary Na(+)-K(+)-ATPase.

Previous studies of hormonal regulation of renal Na(+)-K(+)-ATPase have indicated that the activity of the sodium pump is regulated by phosphorylation-dephosphorylation reactions. Here we report that okadaic acid (OA) and calyculin A (CL-A), inhibitors of protein phosphatase (PP)-1 and PP-2A, inhibited Na(+)-K(+)-ATPase activity in cells from the rat thick ascending limb (TAL) of loop of Henle in a dose-dependent manner. CL-A was 10-fold more potent than OA. On the basis of the inhibitory constant values of CL-A and OA for PP-1 and PP-2A, it is concluded that the tubular effect is mainly due to inhibition of PP-1. In situ hybridization studies with oligonucleotide probes revealed very strong PP-1 alpha and PP-1 gamma 1 mRNA labeling in the outer stripe of the outer medulla, strong labeling in the inner stripe of the outer medulla, and weak labeling in the inner medulla. Very weak labeling was demonstrated in the outer cortex. PP-1 beta mRNA labeling was very strong in the inner stripe of the outer medulla, whereas the outer stripe had weaker labeling, and the inner medulla had weak labeling. PP-1 alpha, PP-1 beta, and PP-1 gamma 1 mRNA were also demonstrated in the transitional epithelium of the ureter. The abundance of the PP-1 alpha and PP-1 gamma isoforms as measured by immunoblotting was very high in tissue from the outer medulla, which also has a high abundance of the endogenous dopamine-regulated PP-1 inhibitor, DARPP-32.(ABSTRACT TRUNCATED AT 250 WORDS)