Type ii na/pi cotransport is regulated at the transcriptional level
by ambient bicarbonate/carbon dioxide tension in ok cells.
Jehle, Andreas W., Helene Hilfiker, Markus F. Pfister, J[umlaut]urg
Biber, Eleanor Lederer, Reto Krapf and Heini Murer.
Institute of Physiology, University of Zurich-Irchel, CH-8057
Zurich, Switzerland; 1Department of Medicine, Division of Nephrology,
University of Louisville, Louisville, Kentucky 40292; 2Klinik B
f[umlaut]ur Innere Medizin, Kantonsspital, CH-9007 St. Gallen,
Switzerland.
APStracts 5:0169F, 1998.
The purpose of the present study was to determine if isohydric changes
in HCO3 concentration and CO2 tension directly affect apical Na
-dependent Pi (Na/Pi) cotransport in OK-cells (opossum kidney cell
line). Cells were kept at either 44 mM NaHCO3/10% CO2, pH 7.4 (high
HCO3/CO2 condition) or 22 mM NaHCO3/5% CO2, pH 7.4 (low HCO3/CO2
condition) (for 14-24 h). Incubation in lower HCO3/CO2 concentrations
increased Na/Pi-cotransport 1.5 fold. The increased Na/Pi-cotransport
was paralleled by a 2-3 fold increased expression of the NaPi-4
transporter protein and a 2-3 fold increase in NaPi-4 mRNA abundance.
The increase in NaPi-4 mRNA could be completely prevented by
incubation in the presence of a transcriptional inhibitor suggesting
that the increase in NaPi-4 mRNA results from an increased NaPi-4
mRNA transcription. In aggreement, the NaPi-4 promoter activity was
stimulated by 50% at lower HCO3/CO2 concentrations. In conclusion:
Our data demonstrate that isohydric changes in HCO3 concentration and
CO2 tension exert a significant, direct cellular effect on Na/Pi
-cotransport and NaPi-4 protein expression in OK-cells by affecting
NaPi-4 mRNA transcription.
Received 14 May 1998; accepted in final form 17 September 1998.
APS Manuscript Number F118-8.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 20 October 1998