Ionic control of locomotion and shape of epithelial cells: II. Role of monovalent cations

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Abstract
The migration of keratocytes isolated from Xenopus tadpole epidermis has been investigated in vitro. In saline the cells move with a mean speed of 5–6 μm/min. Migration is slowed down in saline with diminished sodium content and ceases in media containing not more than 4 mM sodium. Inhibition of the Na+/K+‐2Cl− cotransporter by piretanide reduces the speed of migrating cells to about one‐third of the control level, the same accounts to inhibition of the Na+/H+ antiport with amiloride at pH 7.2. At pH 6.6, however, amiloride only slightly influences locomotion. Depolarization of the plasma membrane by increased extracellular K+ concentration or by inhibition of the Na+/K+ pump by ouabain is only of minor influence during more than 1 h. Hyperpolarization of the cells using the sodium ionophore monensin impedes locomotion; this inhibition depends on an active Na+/K+ pump. Ionophore‐mediated breakdown of the K+ gradient strictly inhibits locomotion. The experiments have shown that a continuous flux of sodium ions is indispensable for the maintenance of cell locomotion. These ions may exert their action primarily by affecting cytosolic free calcium concentration and pH.