Stimulation of proximal convoluted tubule phosphate transport by
epidermal growth factor: signal transduction.
Quigley, Raymond, Donald A. Kennerly, Ji-Nan Sheu, and Michel Baum.
Departments of Pediatrics and Internal Medicine, University of
Texas Southwestern Medical Center at Dallas, Dallas, Texas 75235
-9063
APStracts 2:0053F, 1995.
The present study investigated the signal transduction pathway
responsible for the epidermal growth factor (EGF) stimulation of
phosphate transport in the rabbit proximal convoluted tubule (PCT).
Genistein, 10-4M bath and lumen, an inhibitor of EGF receptor
tyrosine kinase activity, blocked the EGF effect on phosphate
transport (JPhos), consistent with a role for tyrosine kinase in the
signal transduction pathway. Both staurosporine (5 x 10-8M) and
calphostin C (10-8M), inhibitors of protein kinase C blocked the EGF
stimulation of JPhos, indicating that protein kinase C is involved in
EGF signalling. Intracellular calcium concentrations were measured in
perfused tubules using FURA-PE3 to determine if changes in Ca++i were
also part of the signalling pathway. After addition of 3nM EGF, there
was no change in Ca++i, suggesting that stimulation of protein kinase
C is not from phosphatidylinositol hydrolysis by phospholipase C
-gamma (PLC[delta]). To determine if phospholipase A2 (PLA2) is
involved, the inhibitor mepacrine was used. Mepacrine (5 10-5 M) had
no direct effect on PCT transport but blocked the stimulatory effect
of EGF on phosphate transport. Phospholipase A2 activity, assessed as
free arachidonic acid release from proximal tubules in suspension,
increased by 18.8% with 3 nM EGF. Thus, the stimulation of phosphate
transport by EGF is mediated via a signal transduction pathway
involving tyrosine kinase, protein kinase C, and phospholipase A2.
Received 22 September 1994; accepted in final form 28 March 1995.
APS Manuscript Number F339-4.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 April 1995.