Intracellular pH gradients in migrating cells

Abstract

Cell polarization along the axis of movement is required for migration. The localization of proteins and regulators of the migratory machinery to either the cell front or its rear results in a spatial asymmetry enabling cells to simultaneously coordinate cell protrusion and retraction. Protons might function as such unevenly distributed regulators as they modulate the interaction of focal adhesion proteins and components of the cytoskeleton in vitro. However, an intracellular pH (pHi) gradient reflecting a spatial asymmetry of protons has not been shown so far. One major regulator of pHi, the Na+/H+exchanger NHE1, is essential for cell migration and accumulates at the cell front. Here, we test the hypothesis that the uneven distribution of NHE1 activity creates a pHigradient in migrating cells. Using the pH-sensitive fluorescent dye BCECF, pHiwas measured in five cell lines (MV3, B16V, NIH3T3, MDCK-F1, EA.hy926) along the axis of movement. Differences in pHibetween the front and the rear end (ΔpHifront-rear) were present in all cell lines, and inhibition of NHE1 either with HOE642 or by absence of extracellular Na+caused the pHigradient to flatten or disappear. In conclusion, pHigradients established by NHE1 activity exist along the axis of movement.