Subcellular distribution of calcium-sensitive potassium channels (IK1) in migrating cells.

Cell migration is crucial for wound healing, immune defense, or formation of tumor metastases. In addition to the cytoskeleton, Ca2+ sensitive K+ channels (IK1) are also part of the cellular "migration machinery." We showed that Ca2+ sensitive K+ channels support the retraction of the rear part of migrating MDCK-F cells by inducing a localized shrinkage at this cell pole. So far the molecular nature and in particular the subcellular distribution of these channels in MDCK-F cells is unknown. We compared the effect of IK1 channel blockers and activators on the current of a cloned IK1 channel from MDCK-F cells (cIK1) and the migratory behavior of these cells. Using IK1 channels labeled with a HA-tag or the enhanced green fluorescent protein we studied the subcellular distribution of the canine (cIK1) and the human (hIK1) channel protein in different migrating cells. The functional impact of cIK1 channel activity at the front or rear part of MDCK-F cells was assessed with a local superfusion technique and a detailed morphometric analysis. We show that it is cIK1 whose activity is required for migration of MDCK-F cells. IK1 channels are found in the entire plasma membrane, but they are concentrated at the cell front. This is in part due to membrane ruffling at this cell pole. However, there appears to be only little cIK1 channel activity at the front of MDCK-F cells. In our view this apparent discrepancy can be explained by differential regulation of IK1 channels at the front and rear part of migrating cells.