AJP - Regulatory, Integrative and Comparative Physiology, Vol 248, Issue 3 331-R338, Copyright © 1985 by American Physiological Society
Alteration of adipocyte calcium homeostasis by Escherichia coli endotoxin
K. M. Nelson and J. A. Spitzer
The present study evaluated calcium homeostasis in rat adipocytes after
either in vivo or in vitro exposure to Escherichia coli endotoxin. Fat
cells from endotoxin-treated rats showed an enhanced uptake of 45Ca. In an
attempt to differentiate between 45Ca binding to the cell surface and
intracellular 45Ca accumulation, adipocytes were exposed to 5 mM LaCl3. The
amount of 45Ca remaining associated with lanthanum-treated adipocytes was
taken to be located intracellularly and was increased in adipocytes from
endotoxin-treated rats. The amount of 45Ca displaced by lanthanum was also
increased in adipocytes from endotoxin-treated rats. This suggested that
the endotoxin-induced increase of 45Ca accumulation included both cell
surface and intracellular binding sites. Compartmental analysis of the
exchange kinetics of cell-associated 45Ca with 40Ca in the medium indicated
a 77% increase in the size of the cell surface compartment of adipocytes
from endotoxin-treated rats compared with controls. In addition, endotoxin
treatment altered the flux of calcium from the cells to the medium. In
vitro exposure of freshly prepared adipocytes to 250 or 750 micrograms
endotoxin/ml did not produce a perturbation of adipocyte calcium
homeostasis. The results indicate that endotoxin induces alterations in the
ability of adipocytes to regulate calcium translocations, suggesting that
some metabolic and hormonal aspects of endotoxins' actions may be mediated
through perturbation of cellular calcium homeostasis.
