Role of K+ channel expression in polyamine-dependent intestinal epithelialcell migration

Polyamines are essential for cell migration during early mucosal restitutio n after wounding in the gastrointestinal tract. Activity of voltage-gated K + channels (Kv) controls membrane potential (E-m) that regulates cytoplasmi c 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 inhibi tor of polyamine synthesis, alpha-difluoromethylornithine (DFMO, 5 mM), dep leted cellular polyamines (putrescine, spermidine, and spermine), selective ly inhibited Kv1.1 channel (a delayed-rectifier Kv channel) expression, and resulted in membrane depolarization. Because IEC-6 cells did not express v oltage-gated Ca2+ channels, the depolarized E-m in DFMO-treated cells decre ased [Ca2+](cyt) as a result of reduced driving force for Ca2+ influx throu gh capacitative Ca2+ entry. Migration was reduced by 80% in the polyamine-d eficient cells. Exogenous spermidine not only reversed the effects of DFMO on Kv1.1 channel expression, E-m, and [Ca2+](cyt) but also restored cell mi gration 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.