Role of K+ channel expression in polyamine-dependent intestinal epithelial cell migration
Polyamines are essential for cell migration during early mucosal restitution after wounding in the gastrointestinal tract. Activity of voltage-gated K+ channels (Kv) controls membrane potential ( E m) that regulates cytoplasmic free Ca2+ concentration ([Ca2+]cyt) by governing the driving force for Ca2+ influx. This study determined whether polyamines are required for the stimulation of cell migration by altering K+ channel gene expression, E m, and [Ca2+]cyt in intestinal epithelial cells (IEC-6). The specific inhibitor of polyamine synthesis, α-difluoromethylornithine (DFMO, 5 mM), depleted cellular polyamines (putrescine, spermidine, and spermine), selectively inhibited Kv1.1 channel (a delayed-rectifier Kv channel) expression, and resulted in membrane depolarization. Because IEC-6 cells did not express voltage-gated Ca2+ channels, the depolarized E m in DFMO-treated cells decreased [Ca2+]cyt as a result of reduced driving force for Ca2+ influx through capacitative Ca2+ entry. Migration was reduced by 80% in the polyamine-deficient cells. Exogenous spermidine not only reversed the effects of DFMO on Kv1.1 channel expression, E m, and [Ca2+]cyt but also restored cell migration to normal. Removal of extracellular Ca2+ or blockade of Kv channels (by 4-aminopyridine, 1–5 mM) significantly inhibited normal cell migration and prevented the restoration of cell migration by exogenous spermidine in polyamine-deficient cells. These results suggest that polyamine-dependent intestinal epithelial cell migration may be due partially to an increase of Kv1.1 channel expression. The subsequent membrane hyperpolarization raises [Ca2+]cyt by increasing the driving force (the electrochemical gradient) for Ca2+ influx and thus stimulates cell migration.