Calcium gradients underlying polarization and chemotaxis of eosinophils

The concentration of intracellular free calcium (Ca2+]i) in polarized eosinophils was imaged during chemotaxis by monitoring fluorescence of the calcium-sensitive dye Fura-2 with a modified digital imaging microscope. Chemotactic stimuli caused Ca2+]i to increase in a nonuniform manner that was related to cell activity. In cells moving persistently in one direction, Ca2+]i was highest at the rear and lowest at the front of the cell. Before cells turned, Ca2+]i transiently increased. The region of the cell that became the new leading edge had the lowest Ca2+]i. These changes in Ca2+]i provide a basis for understanding the organization and local activity of cytoskeletal proteins thought to underlie the directed migration of many cells.