Hypertonicity activates map kinases and inhibits absorption via
distinct pathways in thick ascending limb.
Iii, Bruns A. Watts, John F. Di Mari, Roger J. Davis and David W.
Good.
1Departments of Medicine and Physiology & Biophysics, University of
Texas Medical Branch, Galveston, Texas 77555 and 2Howard Hughes
Medical Institute, Program in Molecular Medicine, Department of
Biochemistry and Molecular Biology, University of Massachusetts
Medical School, Worcester, Massachusetts 01605
APStracts 5:0131F, 1998.
Mitogen-activated protein (MAP) kinases are activated by osmotic
stress in a variety of cells but their function and regulation in
renal tubules is poorly understood. The present study was designed to
examine the osmotic regulation of MAP kinases in the medullary thick
ascending limb (MTAL) of the rat and to determine their possible role
in the hyperosmotic inhibition of absorption in this segment. Tissue
from the inner stripe of the outer medulla and microdissected MTALs
were incubated at 37o in control (290 mosmol/kg H2O) or hyperosmotic
(300 mM added mannitol) solution for 15 min. Activities of
extracellular signal-regulated kinase (ERK), c-Jun NH2-terminal
kinase (JNK), and p38 MAP kinase were then measured using immune
complex assays. Hyperosmolality increased p38 MAP kinase activity
(2.3-fold) and ERK activity (2.0-fold) but had no effect on JNK
activity (1.1-fold). Exposure to hyperosmolality for various times
showed that the activation of p38 MAP kinase was rapid (( 5 min) and
was sustained for up to 60 min, whereas the activation of ERK was
transient (ERK activity peaked at 15 min, then declined to basal
levels at 30 min). Pretreatment with the MAP kinase kinase inhibitor
PD98059 (15 (M) blocked the hyperosmotic activation of p38 MAP kinase
and ERK but did not prevent hyperosmotic inhibition of absorption.
These results show that hyperosmolality differentially activates p38
MAP kinase and ERK in the MTAL. In contrast, we found no evidence for
involvement of JNK in the early response to hyperosmotic stress.
Eliminating the activation of p38 MAP kinase and ERK does not prevent
hyperosmotic inhibition of absorption, suggesting that
hyperosmolality inhibits apical membrane Na+/H+ exchange (NHE3)
activity via a signaling pathway distinct from these MAP kinase
pathways.
Received 15 December 1997; accepted in final form 22 July 1998.
APS Manuscript Number F396-7.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 21 September 1998