Hepatocyte Growth Factor/Scatter Factor (HGF/SF) stimulates migration of various cells and has been linked via Met tyrosine kinase signaling to transformation and the metastatic phenotype. HGF/SF-Met signaling also plays a role in malignancy. Migration of transformed MDCK-F cells depends on activation of a charybdotoxin (ChTX)-sensitive, volume-activated membrane K+ current. Patch-clamp electrophysiology and transwell migration assays were used to study the effects of HGF/SF on membrane K+ currents and cell migration in MDCK II cells. HGF/SF activated membrane K+ currents that increased over 24 hr, and these could be modulated by altering intracellular free calcium concentration [Ca2+]i. HGF/SF also significantly increased MDCK II cell migration. Specific Ca2+-activated K+ channel blockers, ChTX, iberiotoxin (IbTX), stichodactyla toxin (Stk) and clotrimazole (CLT) inhibited HGF/SF stimulation of membrane K+ currents and cell migration. This suggests that the activation of Ca2+-activated K+ channels is necessary for HGF/SF stimulation of MDCK II cell migration. Furthermore, HGF/SF induced ERK phosphorylation, and addition of the MEK inhibitor PD98059 inhibited ERK phosphorylation, as well as HGF/SF stimulation of Ca2+-activated K+ currents and cell migration in MDCK II cells. Taken together, HGF/SF induces phosphorylation of ERK, which plays a role in HGF/SF activation of Ca2+-activated K+ channels and enhancing cell migration in MDCK II cells.