AJP - Gastrointestinal and Liver Physiology, Vol 258, Issue 6 934-G941, Copyright © 1990 by American Physiological Society
Regulation of ornithine decarboxylase activity in LoVo cells
S. A. McCormack, L. L. Tague, E. J. Gragoe Jr and L. R. Johnson
Department of Physiology and Biophysics, University of Tennessee College of Medicine, Memphis 38163.
The role of Na+ and Na(+)-H+ exchange in the stimulation of ornithine
decarboxylase (ODC) activity has been investigated in a human colon
adenocarcinoma cell line, LoVo. Asparagine (Asn; 10 mM) or 10% fetal bovine
serum (FBS) increased ODC activity from undetectable levels to greater than
500 pmol CO2.mg protein-1.h-1 in 4 h. This increase could be reduced 50% by
concentrations of Na(+)-H+ exchange inhibitors that did not reduce protein
synthesis. (approximately 0.2 mM for amiloride and 0.05 mM for
hexamethyleneamiloride). Asn was able to double the uptake of 22Na+,
whether an ionic (choline chloride) or nonionic (D-mannitol) substance was
substituted for Na+, and the substitution of these compounds as well as
N-methyl-glucamine for Na+ largely prevented the stimulation of ODC by Asn.
Another factor influencing ODC activity was extracellular pH (pHo). When
pHo was lowered, intracellular pH (pHi) also fell, and ODC activity was
reduced. When pHo was raised, pHi also rose, and ODC activity increased.
The well-known correlation between increased pHi and Na+ uptake with the
stimulation of growth may be due to their influence on ODC activity.
