AJP - Cell Physiology, Vol 259, Issue 1 C84-C91, Copyright © 1990 by American Physiological Society
Uptake and metabolism of putrescine in confluent LLC-PK1 cells
M. R. Hauser and J. S. Cook
University of Tennessee-Oak Ridge Graduate School of Biomedical Sciences.
Putrescine is taken up by confluent pig kidney (LLC-PK1) cells at roughly
equal rates over both Na(+)-dependent and Na(+)-independent pathways. The
former is sensitive to 1 mM amiloride, but the latter is not. Uptake rates
are similar at both the apical and basolateral surfaces. The principal fate
of the putrescine is oxidative deamination, yielding a product that appears
to be either gamma-aminobutyraldehyde or delta 1-pyrroline. Most of the
remainder is converted to products tentatively identified as spermidine,
spermine, or another unidentified product; these products as well as
putrescine itself are lost from the cell at either surface. Changing the
extracellular pH in the range of 6.8-8.0 has no affect on putrescine
uptake. Cells acidified to intracellular pH 6.8 show a reduced capacity to
incorporate radioactivity, an effect that may be due to inhibition of
diamine oxidase. Depletion of ATP stores by treating cells with
2-deoxy-D-glucose and NaN3 does not reduce putrescine uptake, suggesting
that the mechanism is not a primary active transporter. The Na(+)-dependent
component of uptake is inhibited by 5-50 microM Hg2+ in a dose-dependent
manner. p-Chloromercuribenzene sulfonic acid (p-CMBS) at high
concentrations (500-1,000 microM) does not affect Na(+)-independent uptake
but in the presence of Na+ depresses total uptake more than Na+ depletion
alone, suggesting that Na+ enhances the binding of p-CMBS to both
transporters. Spermidine and spermine compete with putrescine for uptake,
but a variety of other organic bases and amino acids do not, indicating
that polyamines are transported by mechanisms distinct from the
transporters for those other compounds.
