AJP - Cell Physiology, Vol 256, Issue 4 C756-C763, Copyright © 1989 by American Physiological Society
Regulation of Na+-H+ exchange in normal NIH-3T3 cells and in NIH-3T3 cells expressing the ras oncogene
N. E. Owen, J. Knapik, F. Strebel, W. G. Tarpley and R. R. Gorman
Department of Biological Chemistry and Structure, University of Health Sciences, Chicago Medical School, Illinois 60064.
Our laboratory and others have demonstrated that Na+-H+ exchange can be
regulated by two different pathways; one that is mediated by an inositol
trisphosphate-stimulated increase in intracellular calcium activity, and
one that is mediated by an increase in protein kinase C activity. To
determine whether one of these pathways is more important than the other,
or whether one pathway is physiologically relevant, we employed normal
NIH-3T3 cells (3T3 cells) and NIH-3T3 cells expressing the EJ human bladder
ras oncogene (EJ cells). The EJ cells were chosen because they provide a
genetic model that does not exhibit serum- or platelet-derived growth
factor (PDGF)-stimulated inositol trisphosphate release or Ca2+
mobilization. It was found that serum- or PDGF-stimulated Na+-H+ exchange
was more pronounced in EJ cells than in control 3T3 cells. As expected,
serum- or PDGF-stimulated Na+-H+ exchange in 3T3 cells was inhibited by
chelating intracellular Ca2+ with the intracellular Ca2+ chelator quin2, by
the intracellular Ca2+ antagonist 8-(N,N-diethylamino)octyl
3,4,5-trimethoxybenzoate (TMB-8), and by the calmodulin antagonist
trifluoperazine. In contrast, these agents did not inhibit serum- or
PDGF-stimulated Na+-H+ exchange in EJ cells. Activators of protein kinase C
(e.g., 1-oleoyl-2-acetylglycerol or biologically active phorbol esters)
were found to stimulate Na+-H+ exchange in EJ cells to the same extent as
serum. However, these agents were considerably less effective than serum in
control 3T3 cells. Despite these findings, PDGF did not stimulate
diacylglycerol levels in EJ cells.(ABSTRACT TRUNCATED AT 250 WORDS)
