Regulation of movement speed by intracellular pH during Dictyostelium discoideum chemotaxis.

Evidence is presented that the chemoattractant-induced cytoplasmic alkalinization in the cellular slime mold Dictyostelium discoideum is essential in regulating locomotion speed during chemotaxis. Intracellular pH was manipulated with weak bases, weak acids, and proton-pump inhibition. Speed of locomotion of individual cells was measured during random and chemotactic movement. We found that (i) an increase of cytoplasmic pH increases the speed of randomly moving cells and (ii) the chemoattractant-induced rise in intracellular pH is essential for the increase in directed locomotion speed upon chemotactic stimulation. In addition, our experiments support the hypothesis that ammonia plays a key role in the thermo- and phototaxis of migrating slugs by increasing the locomotion speed of individual cells through changes in intracellular pH.