Ionic control of locomotion and shape of epithelial cells: I. Role of calcium influx.

The role of calcium in the induction of locomotion, control of direction of locomotion, and modulation of shape of epithelial cells derived from Xenopus laevis tadpole epidermis is investigated. Local influx of calcium is achieved by electrophoretic release of small amounts of calcium from a micropipette (tip diameter 0.1-0.5 micron) closely apposed to the cell body or lamella. The cells are made permeable for calcium by calcium ionophore A23187, and they are kept in Ca++-free, Mg++-rich EGTA Ringer. Another method used to induce Ca++ influx is local application of A23187 while cells move in normal culture medium. Influx of Ca++ into the lamella induces a localised increase in thickness and enlargement of the lamella. Stationary cells become active and show movement in the direction of the Ca++ gradient. Fried-egg-shaped cells tend to acquire a semicircular shape and start moving. Moving cells change the direction of their locomotion, following the direction of Ca++ release. Influx of Ca++ in the cell body region induces its contraction concomitant with an increase in lamellar area. These observations suggest the presence of two different Ca++-sensitive components: an actomyosin meshwork in the cell body and an actin gel in the lamella. Influx of Ca++ induces contraction of actomyosin and solation of actin gel. Interaction of these two systems would explain modulation of shape and generation of locomotion in epithelial cells.