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
YorkDNM¯glhidden¯
APStracts 2:0118F, 1995.
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 27 February 1995; accepted in final form 6 June 1995.
APS Manuscript Number F43-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 18 July 1995.