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Departments of 1 Surgery, 3 Physiology, and 5 Pathology, University of Maryland School of Medicine and 2 Baltimore Veterans Affairs Medical Center, Baltimore, Maryland 21201; and 4 Department of Medicine, School of Medicine, University of California, San Diego, California 92103
Expression of voltage-gated K+ (Kv) channel genes is
regulated by polyamines in intestinal epithelial cells (IEC-6 line),
and Kv channel activity is involved in the regulation of cell migration during early restitution by controlling membrane potential
(Em) and cytosolic free Ca2+
concentration ([Ca2+]cyt). This
study tests the hypothesis that RhoA of small GTPases is a downstream
target of elevated [Ca2+]cyt following
activation of K+ channels by increased polyamines in IEC-6
cells. Depletion of cellular polyamines by
-difluoromethylornithine
(DFMO) reduced whole cell K+ currents
[IK(v)] through Kv channels and caused
membrane depolarization, which was associated with decreases in
[Ca2+]cyt, RhoA protein, and cell migration.
Exogenous polyamine spermidine reversed the effects of DFMO on
IK(v), Em,
[Ca2+]cyt, and RhoA protein and restored cell
migration to normal. Elevation of [Ca2+]cyt
induced by the Ca2+ ionophore ionomycin increased RhoA
protein synthesis and stimulated cell migration, while removal of
extracellular Ca2+ decreased RhoA protein synthesis,
reduced protein stability, and inhibited cell motility. Decreased RhoA
activity due to Clostridium botulinum exoenzyme
C3 transferase inhibited formation of myosin II stress
fibers and prevented restoration of cell migration by exogenous
spermidine in polyamine-deficient cells. These findings suggest that
polyamine-dependent cell migration is partially initiated by the
formation of myosin II stress fibers as a result of
Ca2+-activated RhoA activity.
polyamines; intracellular calcium; guanosine 5'-triphosphate-binding protein; potassium channels; restitution; intestinal epithelial cells
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