Protein phosphatase-1 in the kidney: evidence for a role in the
regulation of medullary na+,k+-atpase.
Li, Dailin, Anita Aperia, Gianni Celsi, Edgar F. Da Cruz E Silva, Paul
Greengard, and Bj[diaeresis]orn Meister.
Departments of Woman and Child Health, Pediatric Unit and
Neuroscience, Karolinska Institute, Stockholm, Sweden; and Laboratory
of Molecular and Cellular Neuroscience, Rockefeller University, New
York, New York
APStracts 2:0105F, 1995.
Li, Dailin, Anita Aperia, Gianni Celsi, Edgar F. da Cruz e Silver,
Paul Greengard and Bj[diaeresis]orn Meister. Protein phosphatase-1 in
the kidney: evidence for a role in the regulation of Na+,K+-ATPase in
the medullary thick ascending limb of Henle. Previous studies of
hormonal regulation of renal Na+,K+-ATPase have indicated that the
activity of this enzyme is regulated by phosphorylation /
dephosphorylation reactions. Here we report that okadaic acid (OA)
and calyculin A (CL-A), inhibitors of protein phosphatases (PP) 1 and
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. Based on the KI 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 [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], [beta]
and [gamma]1 mRNA were also demonstrated in the transitional
epithelium of the ureter. The abundance of the PP-1[alpha] and
[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. OA and
fenoldopam (D1 agonist) had no synergistic but an additive inhibitory
effect on Na+,K+-ATPase activity, suggesting that inhibition of PP-1
is one of the mechanisms of DA inhibition of Na+,K+-ATPase activity
in mTAL. The results support the concept that the DARPP-32/PP-1
system plays an important role in the regulation of Na+,K+-ATPase in
the thick ascending limb of Henle.
Received 7 February 1995; accepted in final form 6 June 1995
APS Manuscript Number F0043-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.