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Regulation of Na+/H+ Exchanger by Urogastrone,
a Potent Activator of Cell Proliferation
K. BARIŠIĆ, O. KARUŽIĆ, J.
PETRIK, T. Ž. GRUBIŠIĆ
University of Zagreb, Faculty of Pharmacy and
Biochemistry, Department of Medical Biochemistry and Hematology,
Zagreb, Croatia
Received
November 1, 2001
Accepted March 7, 2002
Summary
We tested the effects of epidermal growth factor (EGF) on Na+/H+
exchanger (NHE) activity using urogastrone for treatment of
Wistar rats and rat kidney tissue slices. NHE activity was
monitored in isolated kidney brush border membrane vesicles by
following fluorescence quenching of acridine orange. A
significant increase of NHE activity was detected as early as 5
min after addition of urogastrone to rat kidney slices in vitro.
In Wistar rats treated with urogastrone we also found increased
NHE activity (by about 12 %). Both changes of NHE activity were
the result of a significant rise of Vmax value and an apparent
decrease in Km value in in vitro experiments. The rise of NHE
activity caused by urogastrone was sensitive to the inhibitors
of transcription and translation. The presence of phosphatase
inhibitor, NaF, elevated NHE activity of non-stimulated as well
as of urogastrone-stimulated exchanger, suggesting that
phosphorylation plays an important role in Na+/H+ exchange.
Osmolarity of the medium seems to regulate NHE activity in such
a manner that both hyper- and hypoosmolar conditions inhibited
NHE activity. The absence of Ca2+ions produced a 60 % decrease
of NHE activity. The chemical modification of histidine residues
with diethyl pyrocarbonate or SH groups with N-ethylmaleimide
inhibited NHE activity.
Key
words
Na+/H+ exchanger · Kidney brush border membrane vesicles ·
Epidermal growth factor · Urogastrone
Reprint
requests
Karmela Barišić, University of Zagreb, Faculty of Pharmacy and
Biochemistry, Department of Medical Biochemistry and Hematology,
A. Kovačića 1, Zagreb, Croatia; e-mail:
karmela.barisic@fbf.tel.hr
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