Vasopressin stimulates sodium transport in a6 cells through a
phosphatidylinositide 3-kinase dependent pathway.
Edinger, R. S., M. D. Rokaw, and J. P. Johnson.
Renal-Electrolyte Division, University of Pittsburgh, School of
Medicine
APStracts 6:0119F, 1999.
The enzyme phosphatidylinositide 3-kinase (PI3K) phosphorylates the D
-3 position of the inositol ring of inositol phospholipids and
produces 3-phosphorylated inositides. These novel second messengers
are thought to mediate diverse cellular signaling functions. The
fungal metabolite wortmannin covalently binds to PI3K and selectively
inhibits its activity. The role of PI3K in basal and hormone
stimulated transepithelial sodium transport was examined using this
specific inhibitor. 50 nM wortmannin did not affect basal,
aldosterone-stimulated, or insulin stimulated transport in A6 cells.
Wortmannin completely inhibits vasopressin stimulation of transport
in these cells. Vasopressin stimulates PI3K activity in A6 cells.
Vasopressin stimulation of transport is also blocked by 5 mM
LY294002, a second inhibitor of PI3K. One hour pre-incubation with
wortmannin blocked vasopressin stimulation of protein kinase A
activity in the cells. Sodium transport response to exogenous cAMP
and forskolin, which directly activates adenylate cyclase, were not
affected by wortmannin. These results indicate that wortmannin
inhibits vasopressin stimulation of Na- transport at a site proximal
to activation of adenylate cyclase. The results suggest that PI3K may
be involved in receptor activation by vasopressin.
Received 18 September 1998; accepted in final form 8 June 1999.
APS Manuscript Number F238-8.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 25 June 1999